Open Collections

UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Resource availability and limitation for a cavity-nesting community in mature conifer forests and aspen… Aitken, Kathryn Elizabeth Helen 2007

Your browser doesn't seem to have a PDF viewer, please download the PDF to view this item.

Item Metadata

Download

Media
831-ubc_2007-317266.pdf [ 5.77MB ]
Metadata
JSON: 831-1.0074957.json
JSON-LD: 831-1.0074957-ld.json
RDF/XML (Pretty): 831-1.0074957-rdf.xml
RDF/JSON: 831-1.0074957-rdf.json
Turtle: 831-1.0074957-turtle.txt
N-Triples: 831-1.0074957-rdf-ntriples.txt
Original Record: 831-1.0074957-source.json
Full Text
831-1.0074957-fulltext.txt
Citation
831-1.0074957.ris

Full Text

R E S O U R C E A V A I L A B I L I T Y A N D L I M I T A T I O N F O R A C A V I T Y - N E S T I N G C O M M U N I T Y I N M A T U R E C O N I F E R F O R E S T S A N D A S P E N G R O V E S I N I N T E R I O R B R I T I S H C O L U M B I A by Kathryn Elizabeth Helen Aitken B . S c , Simon Fraser University, 1999 M . S c , University of British Columbia, 2002 A THESIS S U B M I T T E D I N P A R T I A L F U L F I L L M E N T OF T H E R E Q U I R E M E N T S F O R T H E D E G R E E OF D O C T O R OF P H I L O S O P H Y in The Faculty of Graduate Studies (Forestry) T H E U N I V E R S I T Y OF B R I T I S H C O L U M B I A August 2007 © Kathryn Elizabeth Helen Aitken, 2007 A B S T R A C T Nest-site availability limits cavity-nesting populations in harvested forests, and woodpeckers are often considered keystone species because they influence the abundance of other cavity-nesters in the community. However, little is known about the relative importance of excavated versus non-excavated holes for cavity-nesters, and the extent of nest-site limitation in mature forests. I analyzed data from 1371 holes used by 29 bird and mammal species between 1995-2006. Excavated cavities were more abundant than non-excavated and were smaller and higher above ground, but were used in proportion to their availability. To test the hypothesis that nest-site availability limited cavity-nester abundance in mature forests, I conducted two multi-year, replicated before-after/control-impact (BACI) experiments in which I altered nest-site availability. In coniferous forests, which had low cavity densities (1.9/ha) and low occupation rates (9%) prior to treatment, I added nest boxes within the size ranges of the most common excavators (northern flicker Colaptes auratus and red-naped sapsucker Sphyrapicus nuchalis). Densities of mountain chickadees (Poecile gambeli), red squirrels (Tamiasciurus hudsonicus), and northern flying squirrels (Glaucomys sabrinus) increased following box addition and returned to pre-treatment levels following box removal. In aspen groves, which had high cavity densities (16/ha) and relatively high occupancy rates (44%) prior to my experiment, I blocked the entrances of high quality cavities (those with a high probability of occupancy). Total nest abundance declined by 49% on treatment sites following cavity blocking and returned to pre-treatment levels once cavities were reopened. Nest abundance of European starlings (Sturnus vulgaris), a dominant secondary cavity-nester, declined by 89% and failed to recover post-treatment. Conversely, nest abundance of mountain bluebirds (Sialia currucoides; a subordinate secondary cavity-nester) increased following cavity blocking and remained high following reopening. While woodpeckers provide an abundant supply of cavities in some mature forests, non-excavated holes may release secondary cavity-nesters from the constraints of excavator nest-site preferences. Additionally, while nest-sites may appear to be abundant and potentially non-limiting at the community level, individual species preferences, as well as interspecific interactions, may influence true nest-site availability, particularly for mountain chickadees, starlings, and small mammals. T A B L E O F C O N T E N T S A B S T R A C T i i T A B L E OF C O N T E N T S . .. iv LIST O F T A B L E S . . . . . '. v i i L I S T O F F I G U R E S ix A C K N O W L E D G E M E N T S x i D E D I C A T I O N x i i C O - A U T H O R S H I P S T A T E M E N T x i i i C H A P T E R 1: G E N E R A L I N T R O D U C T I O N A N D THESIS O V E R V I E W 1 General introduction 1 The importance of excavated versus non-excavated holes for cavity-nesters 2 The role of nest-site availability in limiting cavity-nesting populations 3 Nest-site availability and limitation in mature forests of interior British Columbia : 4 Thesis Objectives...- 5 Study area 5 Thesis overview.. 6 References 12 C H A P T E R 2: T H E I M P O R T A N C E OF E X C A V A T O R S TN C A V I T Y - N E S T I N G C O M M U N I T I E S : A V A I L A B I L I T Y A N D U S E OF N A T U R A L T R E E C A V I T I E S IN O L D M I X E D F O R E S T S OF W E S T E R N C A N A D A 17 Introduction 17 Methods , : 18 Study Area 18 Nest location and monitoring 19 Nest tree and cavity characteristics 20 Availabil i ty of excavated and non-excavated cavities 20 Data analyses 21 Results : • • 22 Excavated versus non-excavated cavities used for nesting 22 Availabil i ty of excavated versus non-excavated cavities 24 iv Discussion ; 24 References 37 C H A P T E R 3: D O E S N E S T - S I T E A V A I L A B I L I T Y L I M I T C A V I T Y - N E S T E R S I N M A T U R E F O R E S T S OF I N T E R I O R B R I T I S H C O L U M B I A ? A N E S T B O X A D D I T I O N E X P E R I M E N T . 42 Introduction 42 Methods .45 Study Area 45 Nest monitoring and box addition experiment 45 Data analyses 47 ' Results 1 47 Discussion 49 Response of mountain chickadees to box addition 50 Response of red squirrels and northern flying squirrels to box addition 52 Response of red-breasted nuthatches to box addition 53 Conclusions '.. 54 References 59 C H A P T E R 4: R E S P O N S E OF S E C O N D A R Y C A V I T Y - N E S T E R S T O A N E X P E R I M E N T A L R E D U C T I O N I N C A V I T Y A V A I L A B I L I T Y : R E S O U R C E S E L E C T I O N P L A S T I C I T Y A N D SPECIES I N T E R A C T I O N S 67 Introduction 67 Methods..... 68 Study area ; 68 Nest monitoring and cavity blocking experiment 69 Data analyses 69 Results 70 Discussion 71 Response of European starlings to cavity blocking 71 Response of mountain bluebirds and tree swallows to cavity blocking 73 Role of interspecific dominance in species' responses to cavity blocking 73 Experiments on population limitation in cavity-nesters 75 Conclusions 75 References .- 79 C H A P T E R 5: G E N E R A L D I S C U S S I O N A N D C O N C L U S I O N S 86 Thesis summary. 86 v Knowledge gaps and suggestions for future research 87 Intra- and interspecific partitioning of cavities : 87 Influence of competition and predation by small mammals on cavity availability and selection 89 Summary 91 References 91 vi L I S T O F T A B L E S Table 1.1. Linear mixed-effects model predicting nest density of cavity-nesting birds and mammals in mature coniferous forests and aspen groves in interior British Columbia, Canada in 2000 and 2001, in relation to cavity density. Year was included in the model as a random effect. Data were log-transformed for analysis 8 Table 1.2. Cavity-nesting bird and mammal species found in aspen groves and coniferous forests near Riske Creek, British Columbia, 1995-2006. Primary nesting habitat is indicated as "Coniferous" or "Aspen groves" when >60% of a species' nests were located in those forest types; "Both" indicates that - 5 0 % of a species' nests occurred in each habitat. For species with n < 5, the predominant nesting habitat is shown in brackets. Total sample size'of nests is n = 2262 for the study 9 Table 2.1. B i rd and mammal species nesting in excavated and non-excavated tree cavities, and percent of total cavities excavated by woodpecker and other excavator species in interior British Columbia, Canada, 1995-2006. See Table 1.2 for scientific names of species 29 Table 2.2. Linear mixed effects models predicting nest-site characteristics of cavity-nesting birds and mammals in interior British Columbia, Canada, between 1995-2006. Separate models were built for each of six nest-site characteristics, with cavity type ("excavated", "non-excavated") as the fixed effect, and individual cavity as the random effect. A positive estimate indicates that excavated cavities had a higher mean value than non-excavated cavities, and vice versa for negative estimates. Confidence intervals that do not encompass zero are highlighted in bold. See Table 1.2 for species scientific names. 31 Table 2.3. Characteristics of available excavated and non-excavated cavities surveyed in coniferous forests and aspen groves in 2000 33 Table 3.1. M i x e d models predicting density of a) all nests of cavity-nesting birds and mammals, b) mountain chickadee nests, c) red squirrel and northern flying squirrel nests and roosts, and d) red-breasted nuthatch nests in relation to treatment type (box addition or control) and treatment period (pre-treatment, during treatment or post-treatment). Linear mixed effects ( L M E ) models were used to examine chickadee density, while generalized linear mixed-effects models ( G L M M ) were used to examine nuthatch and squirrel densities. L M E and G L M M calculate separate parameter estimates for each level of categorical fixed effects, and report estimates in relation to the first level specified in the data alphabetically. Thus, parameters were calculated in relation to Treatment type = "Box addition" and Period = "During treatment". For example, the significant negative parameter estimate for total bird and mammal nests in the pre-treatment period indicates that nest density was significantly lower in that period than during treatment. Site was included in the model as a random effect 55 Table 4.1. Generalized linear mixed models ( G L M M ) predicting abundance of a) total bird and mammal cavity nests, b) European starling nests, c) mountain bluebird nests, and d) tree swallow nests in relation to treatment type (cavity blocking or control) and treatment period (pre-blocking, during blocking or post-blocking). G L M M calculates separate parameter estimates for each level of categorical fixed effects, and reports estimates in relation to the first level specified in the data alphabetically. Thus, parameters reported here were calculated in relation to Treatment type = "Blocking" and Period = "During blocking ". For example, the significant positive parameter estimate for total bird and mammal nests in the pre-blocking period indicates that nest abundance was significantly higher in that period than during treatment. Site was included in the model as a random effect 77 v i i i L I S T O F F I G U R E S Figure 1.1. Relationship between density of cavity-nesting birds and mammals and total cavity density in a) aspen groves and b) mature coniferous forest in interior British Columbia in 2000 and 2001. See text for results of statistical tests 10 Figure 1.2. Map of British Columbia indicating the location of the study area near Wil l iams 1 Lake, and aerial photograph of the study area with study sites labelled 11 Figure 2.1. Characteristics of excavated and non-excavated cavities used by all species ("Total nests"), and by five individual species. See Table 1.2 for full species names, and Table 2.2 for results of mixed models analyses 34 Figure 2.2. Distance of nests in excavated and non-excavated cavities to nearest edge in aspen groves and in coniferous forest sites. See Table 1.2 for full species names, and Table 2.2 for results of mixed models analyses 35 Figure 2.3. Orientation of a) excavated and b) non-excavated cavities. The arrow indicates mean orientation and the arcs to either side indicate the 95% confidence interval. See text for results of statistical tests , 36 Figure 3.1. Proportion of boxes used by a) mountain chickadees, and b) red squirrels and northern flying squirrels compared to proportion of boxes available in dry grassland edge, wet (lake) edge, and forest interior on treatment (box addition) sites in 2002 and 2003. See text for results of Fisher's Exact and chi-square tests 57 Figure 3.2. Density of cavities or boxes occupied by a) all cavity-nesting bird and mammal species, b) mountain chickadees, c) red squirrels and northern flying squirrels (nests and roosts), and d) red-breasted nuthatches on treatment (boxes added) and control sites. Numbers above error bars are the total active nests on treatment sites, and numbers below bars are the total active nests on control sites. See text for details of statistical analyses... 58 ix Figure 4.1. Mean nest abundance of a) all cavity-nesting birds and mammals, b) European starlings, c) mountain bluebirds, and d) tree swallows on 7 treatment (cavity blocking) and 13 control sites at Riske Creek, B C . Sample sizes shown beside points are the total sample of nests ; 78 x A C K N O W L E D G E M E N T S I would first like to thank my supervisor, Dr. Kathy Martin. In the ten years I have known and worked with her, she has been a mentor and a friend, providing guidance, encouragement, support and advice both academically and personally. M y supervisory committee, Drs. Peter Arcese, Jonathan Shurin and the late James N . M . Smith, provided invaluable input in the design and analysis of my study, and in the writing and revision of my thesis. I would like to thank the numerous field technicians who helped to collect the data used in my study. In particular, Dayani Gunawardana, A l i c i a Newbury, Tracy Sutherland, and Ryan Wilds provided excellent assistance and friendship during the 2000-2003 field seasons. David Bradley, Martin Lankau, and Marty Mossop built some of the nest boxes used in my study. Numerous past and present members of the Martin lab, including Andrea Norris, Mark Drever, Alaine Camfield, Brad Fedy, Heather Bears, Lisa Mahon, Jose Luis Rangel Salazar, Scott Wilson, Kristina Cockle, Lesley Evans Ogden, and Nancy Mahony, provided advice and moral support. Dr. Karen Wiebe of the University of Saskatchewan was an early inspiration and provided advice, friendship, data and nest boxes. Finally, I am grateful for the support, encouragement, and love of my family: my husband Marty Mossop, my son Joey, my parents Madeline and Robert Aitken, and my in-laws Grace and Dave Mossop, and Tara, Erin, Iliana and Ada Stehelin. I could not have accomplished this without them. N O T E : Although I have adopted the convention of using the first-person throughout the thesis, I acknowledge that some of the data used in Chapters 2 and 3 were collected during the long-term "Nest Web" project, directed by my supervisor, Dr. Kathy Martin, U B C . I was personally involved in the data collection from 1997-2005 (as an undergraduate field assistant and project manager from 1997-1999 and as a graduate student from 2000-2005). x i DEDICATION This dissertation is dedicated to my son, Joseph Martin Aitken-Mossop. CO-AUTHORSHIP STATEMENT This study was designed collaboratively by Kathryn Aitken and Dr. Kathy Martin. Kathryn Aitken collected the data in the field (1997-2005) with the aid of field assistants, analyzed all data, and prepared the manuscript under the guidance of Dr. Martin. C H A P T E R 1: G E N E R A L I N T R O D U C T I O N A N D T H E S I S O V E R V I E W G E N E R A L I N T R O D U C T I O N The use of shelters such as tree cavities, burrows and shells for breeding, roosting, and protective cover is common in many animal taxa. One or a few species create these resources, which are then occupied by secondary users that are unable to create their own shelters. For example, soft-bodied hermit crabs (Anomura: Superfamily Paguroidea) require empty gastropod shells for protection from predators (Hazlett 1981). Several bird species including golden-shouldered parrots (Psephotus spp.), parakeets (Brotogeris spp.), trogons (Trogon spp.), and kingfishers (Todiramphus spp.), as well as caimans (Paleosuchus spp.), African giant rats (Cricetomys gambianus), and eumenid wasps (Hymenoptera: Eumenidae) raise their offspring in or on termitaria, which provide heat and cover (Ajayi 1977, Batra 1979, Weaver 1982, Magnusson et al. 1985, Brightsmith 2000, Kesler and Haig 2005). Prairie dog (Cynomys spp.) burrows provide shelter and nest sites for burrowing owls (Athene cunicularid) and for other birds, mammals, reptiles, and amphibians (Clark et al. 1982, Desmond and Savidge 1996). However, availability of shelters is limited for many of these secondary users (Vance 1972, Abrams et al. 1986, Newman 1987, Lindenmayer et al. 1991, Newton 1994, McCa l lum et al. 2001), and the costs and benefits of acquiring or defending critical but limited shelters provided by other species results in hierarchical nidic structure, or "nest webs", analogous to trophic structure in food webs (Martin and Eadie 1999). Species that rely on tree cavities form one of the largest groups of shelter users. These species, which include birds, mammals, reptiles, amphibians, and insects, use holes in trees for nesting, roosting, food storage, and cover. Approximately 85 bird and 20 mammal species in Canada and the continental United States use tree cavities (Burt and Grossendeider 1980, Ehrlich et al. 1988, Martin and Scotton unpubl. data), and five percent of European bird species are 1 obligate hole-nesters (Newton 1994). Cavity-nesting communities are structured hierarchically in a nest web of interdependencies based on nesting, foraging and other interactions (Martin and Eadie 1999, Martin et al. 2004). Woodpeckers, or primary cavity excavators, create holes for nesting and roosting. Some woodpeckers use old cavities but little is known about the costs and benefits of reuse for these excavator species (Wiebe et al. 2007). Cavities created by woodpeckers are used by secondary cavity nesters, a diverse group, including passerines such as bluebirds (Sialia spp.) and some swallows (Tachycineta spp.), several species of ducks and raptors, and some small mammals. Because secondary cavity-nesters cannot excavate their own nest holes, they are dependent on those provided by woodpeckers, or on naturally occurring holes caused by tree decay or damage. Weak cavity excavators, including nuthatches (Sitta spp.) and some chickadees (Poecile spp.), may excavate a cavity on their own, enlarge a hole begun by a woodpecker, or use a naturally occurring non-excavated hole (Aitken et al. 2002). The importance of excavated versus non-excavated holes for cavity-nesters Woodpeckers are considered keystone species in some forest communities and can influence the diversity and abundance of other members of the community (Van Balen et al. 1982, Dai ly et al. 1993, Mikuskinski and Angelstam 1998, Martin and Eadie 1999, Aubry and Raley 2002, Duncan 2003). For example, woodpeckers may act as physical ecosystem engineers by excavating nesting and roosting cavities that are used by other cavity-nesting species in the community, by creating foraging opportunities for other species through excavation of feeding holes, sapwells, and bark-scaling, and by accelerating tree decay processes and heartrot inoculation (Ehrlich and Eaily 1988, Jones et al. 1994, 1997, Aubry and Raley 2002, Duncan 2003, Conner et al. 2004, Martin et al. 2004). Woodpeckers may also serve as indicators of species richness and abundance in forest communities, and of overall forest health (Angelstam and Mikusinski 1994, Mikusinski et al. 2001, Remm et al. 2006). 2 In addition to woodpecker-excavated cavities, naturally-occurring non-excavated holes provide nest and roost sites for cavity-nesting species. These holes develop through a variety of mechanisms, including tree limb or top breakage, loosening of bark, wound openings, and a range of fungal and disease processes. However, little is known about the relative abundance and importance of excavated versus non-excavated holes for cavity-nesters in undisturbed forest ecosystems (Martin and Wesplowski, in review). The value of excavators as cavity providers may depend on the abundance of naturally occurring non-excavated holes (Carlson et al. 1998, Remm et al. 2006, Wesolowski in review). Non-excavated holes may free secondary cavity-nesters from the constraints of woodpecker nest-site characteristics and habitat selection, and offer excavator species alternate nesting options i f time or energy for excavation is limited. However, i f non-excavated cavities are scarce in the landscape then it may be difficult for secondary users to locate holes with suitable characteristics or in optimal habitat. In that case, excavated holes may provide the most options for secondary users, particularly i f the • woodpecker assemblage in the community is diverse. The role of nest-site availability in limiting cavity-nesting populations Because cavity-nesters depend on trees for nesting and other activities, they are considered sensitive to forest harvesting (Angelstam and Mikusinski 1994, Newton 1994) and the presence of suitable nest-sites limits some populations of obligate cavity-nesters (Scott 1979, Newton 1994, Bock and Fleck 1995): This is especially true for secondary cavity-nesting species, which' cannot excavate their own cavities. Weak excavators, which require soft decaying substrate, may be limited by the availability of dead or dying trees (Steeger and Hitchcock 1998). These trees may be rare in some forests because they are susceptible to wind throw and are often removed or knocked down during logging operations (Thomas et al. 1979, De Long et al. 2004). In interior British Columbia, more than 90% of cavity nests were located in dying or dead 3 trembling aspen, which made up only 10-15% of trees in the landscape (Martin and Eadie 1999, Martin et al. 2004). However, most studies of nest-site limitation in cavity-nesters have been conducted in managed forests in which the natural assemblage of excavator species may have been altered, and in which essential habitat features such as standing dead and unhealthy trees have been removed (Newton 1994). The few studies conducted in mature forests in which natural rates of cavity creation and loss have not been altered suggest that predation and food availability may be the main factors limiting cavity-nesting populations in those systems (Wesolowski 1989). Species in communities structured around a central resource such as tree cavities may adopt a variety of strategies to acquire that resource. Plasticity in resource selection may allow individuals to reduce interspecific competition and to adapt to temporal and spatial changes in resource availability (Albano 1992, Cuervo 2004, Forstmeier and Weiss 2004, Eggers et al. 2006). Generalist species may be better able to withstand stochasticity in resource availability than specialists (Pimm and Pimm 1982, Palmer 2003), while specialists may put more effort into acquiring a limited number of higher quality resources. Species in cavity-nesting communities display a range of resource acquisition and competitive strategies, thus providing an excellent system in which to examine the importance of ecological plasticity in community responses to changes in resource availability and quality. Nest-site availability and limitation in mature forests of interior British Columbia The Cariboo-Chilcotin region of interior British Columbia consists of mature mixed conifer forests, and native grassland interspersed with small groves of trembling aspen (Populus tremuloides). There are 42 species of cavity-using birds and small mammals in the region, including 8 of 12 woodpecker species found in the province (Martin et al. 2004), and almost one-quarter of the bird species in the region are cavity-nesters. Cavity density ranges from low (1.9/ha) i n coniferous forests to h igh (16/ha) in aspen groves, and occupancy rates vary from 9% i n coniferous forests to 4 4 % i n aspen groves ( A i t k e n 2002, A i t k e n and M a r t i n 2004). I found a posi t ive relat ionship between nest density and cavi ty density (curve est imation procedure, S P S S Inc. 2002; aspen groves: 2000, quadratic mode l , R2 = 0.69, F2,28 = 31.3, P < 0 .0001, 2001, linear mode l , R2 = 0.47, F,, 2g = 25.4, P < 0.0001, Figure 1.1a; coniferous forests: 2000: l inear mode l , R2 = 0.06, Fi, 5 = 0.30, P = 0.61, 2001: linear mode l , R2 = 0.004, FL 5 = 0.02, P = 0.89, Figure 1.1b), w h i c h m a y indicate nest-site l imi ta t ion (Raphael and W h i t e 1984, N e w t o n 1994). C a v i t y density was a significant predictor o f nest density i n both aspen groves and coniferous forests i n the study area (linear mixed-effects mode l ; Table 1.1). THESIS OBJECTIVES M y study addressed the general question o f h o w plast ic i ty i n nest-site select ion enables species and communi t ies to respond to fluctuations i n abundance and qual i ty o f a c r i t ica l resource (nesting cavities). M y objectives were to examine the importance o f excavated versus non-excavated holes for cavity-nesting birds and mammals (Chapter 2), and to determine whether cavi ty abundance l imi t s cavity-nester populations i n mature m i x e d conifer forests (Chapter 3) and aspen groves (Chapter 4). STUDY AREA F i e l d w o r k was conducted i n mature coniferous forests (80-200 yr old) and aspen groves on Becher ' s Prai r ie , near the communi ty o f R i s k e Creek (51° 5 2 ' N , 1 2 2 ° 2 1 ' W , 850-1000m elevation; F igure 1.2). Coniferous forests (>100 ha) were dominated b y lodgepole pine (Pinus contorta var. latifolia), w i t h va ry ing amounts o f Douglas- f i r (Pseudotsuga menziesii var. glauca), hybr id whi te -Engelmann spruce (Picea glauca x engelmanni), and aspen ( M a r t i n et a l . 2004). These forests bordered on grassland or lakes. A s p e n groves ranged i n size from just a few trees to several hectares, and were scattered throughout the grassland matrix. Some were surrounded by grassland while others bordered on ponds or marshes. Table 1.2 presents a summary of the 28 cavity-nesting bird and mammal species nesting on my study sites between 1995-2006, and indicates their primary nesting habitat (coniferous forest or aspen groves), based on the proportion of nests found in each habitat type. See individual data chapters for details of specific study sites and methodology. T H E S I S O V E R V I E W In Chapter 2,1 examined the relative availability and use of excavated and non-excavated cavities in aspen groves and coniferous forest between 1995-2006. I compared cavity, tree and habitat characteristics of excavated and non-excavated holes used for nesting at the community-level, and for five individual species (northern flicker Colaptes auratus, mountain chickadee Poecile gambeli, mountain bluebird Sialia currucoides, tree swallow Tachycineta bicolor, and European starling Sturnus vulgaris). I found that, while excavated cavities were much more abundant than non-excavated cavities and species from all three guilds used non-excavated holes, most species appeared to use them in proportion to their availability. I then reviewed the findings of the few previous studies that examined excavated versus non-excavated holes for cavity-nesters, and discussed the possible advantages for secondary cavity-nesters and excavators that use non-excavated holes. In Chapter 3,1 examined nest-site limitation in mature coniferous forests with low cavity densities and occupation rates, using a box addition experiment. I compared nest densities for all cavity-nesting species combined, as well as for several individual species (mountain chickadee, red-breasted nuthatch, red squirrel, and northern flying squirrel) on treatment (box addition) and control sites over an 11-year period (six years pre-treatment, two years during treatment, and three years following box removal). I found that nest densities of mountain chickadees and 6 nuthatches, and nest and roost densities of squirrels increased significantly following the experimental increase in nest-site availability, and returned to pre-treatment levels when boxes were removed. I then reviewed recent studies examining limitation of cavity-nester populations in mature forests, and interpreted my results in light of chickadee, nuthatch, and squirrel social behaviour and life history strategies. In Chapter 4,1 examined the potential for nest-site limitation in aspen groves with high cavity densities by blocking the entrances of high quality cavities (those with past high occupancy rates). Using generalized linear mixed-effects models, I compared nest abundance of all cavity-nesting species combined, as well as for several individual species (European starlings, mountain bluebirds and tree swallows) on treatment and control sites for two years prior to treatment, two years during treatment, and two years following cavity reopening. I found that species with generalist nest cavity preferences displayed high resistance in nest abundance following the experimental decrease in nest-site availability, while the most dominant, specialist cavity-nester, European starling, displayed low.resistance and resilience to cavity blocking. I also found that mountain bluebirds, a subordinate secondary cavity-nester, appeared to be limited by starling nest abundance. I discuss the implications of generalist versus specialist resource acquisition strategies in determining the response to perturbation, as well as dominance and competitive ability, for cavity-nesters using temporally or spatially variable resources. In chapter 5,1 summarized the conclusions of my research chapters. I also provided a summary of knowledge gaps in cavity-nester community and population ecology, and suggested directions for future research that could address these questions. Chapters 2, 3, and 4 are written as stand-alone manuscripts. 7 Table 1.1. Linear mixed-effects model predicting nest density of cavity-nesting birds and mammals in mature coniferous forests and aspen groves in interior British Columbia, Canada in 2000 and 2001, in relation to cavity density. Year was included in the model as a random effect. Data were log-transformed for analysis. Parameter Estimate SE df -^statistic P Intercept -0,78 0.19 72 -4.2 0.0001 Log cavity density 1.78 0.24 72 7.5 <0.0001 Site type (conifer forest or aspen grove) -0.60 0.33 72 -1.82 0.07 8 Table 1.2. Cavity-nesting bird and mammal species found in aspen groves and coniferous forests near Riske Creek, British Columbia, 1995-2006. Primary nesting habitat is indicated as "Coniferous" or "Aspen groves" when >60% of a species' nests were located in those forest types; "Both" indicates that - 5 0 % of a species' nests occurred in each habitat. For species with n < 5, the predominant nesting habitat is shown in brackets. Total sample size of nests is n = 2262 for the study. Nesting Total Species Code habitat nests Primary cavity excavators Red-naped sapsucker (Sphyrapicus nuchalis) R N S A Both 214 Downy woodpecker {Picoides pubescens) D O W O Coniferous 24 Hairy woodpecker (Picoides villosus) H A W O Coniferous 36 American three-toed woodpecker (Picoides dorsalis) A T T W Coniferous 6 Black-backed woodpecker (Picoides arcticus) B B W O (Coniferous) 2 Northern flicker (Colaptes auratus) N O F L Aspen groves 348 Pileated woodpecker (Dryocopus pileatus) PIWO Coniferous 17 Weak cavity excavators Black-capped chickadee (Poecile atricapillus) B C C H Both 35 Red-breasted nuthatch (Sitta canadensis) R B N U Coniferous 154 Secondary cavity nesters Wood duck (Aix sponsa) W O D U (Aspen groves) 1 Bufflehead (Bucephala albeola) B U F F Aspen groves 59 Barrow's goldeneye (Bucephala islandica) B A G O Aspen groves 5 Hooded merganser (Lophodytes cucullatus) H O M E (Aspen groves) 2 American Kestrel (Falco sparverius) A M K E Aspen groves 40 Flammulated owl (Otus flamfneolus) F L O W (Aspen groves) 1 Northern saw-whet owl (Aegolius acadicus) N S W O Aspen groves 18 Northern hawk owl (Surnia ulula) N H O W (Aspen groves) 2 Tree swallow (Tachycineta bicolor) T R E S Aspen groves 257 Mountain chickadee (Poecile gambeli) M O C H Both 333 Mountain bluebird (Sialia currucoides) M O B L Aspen groves 266 European starling (Sturnus vulgaris) E U S T Aspen groves 340 Northern flying squirrel (Glaucomys sabrinus) G L S A Coniferous 17 Bushy-tailed woodrat (Neotoma cinerea) N E C I Aspen groves 7 Red squirrel (Tamiasciurus hudsonicus) T A H U Both 73 Chipmunk spp. (Eutamias spp.) (Coniferous) 2. Short-tailed weasel (Mustela erminea) M U E R (Aspen groves) 1 Fisher (Martes pennanti) M A P E (Coniferous) 1 Deer mouse (Peromyscus maniculatus) P E M A (Aspen groves) 1 40.0- a) Aspen groves o 2000 • 2001 30.04 w •S 20.0 CO t3 10.04 0.0 10.0 20.0 30.0 ^ ] b) Coniferous forest 0.3 • 40.0 50.0 60.0 0.2 4 o.i4 0.0 o o 0.0 .2 .4 .6 . .8 1.0 1.2 1.4 1.6 1.8 Cavity density Figure 1.1. Relationship between density of cavity-nesting birds and mammals and total cavity density in a) aspen groves and b) mature coniferous forest in interior British Columbia in 2000 and 2001. See text for results of statistical tests. 10 Riske Creek area Figure 1.2. Map of British Columbia indicating the location of the study area near Williams Lake, and aerial photograph of the study area with study sites labelled. R E F E R E N C E S Abrams, P., C. Nyblade, and S. Sheldon. 1986. Resource partitioning and competition for shells in a subtidai hermit crab species assemblage. Oecologia 69: 429-445. Aitken, K . E . H . 2002. Nest-site availability, selection and reuse in a cavity-nesting community in forests of interior British Columbia. M S c thesis: University of British Columbia, Vancouver, B C . Aitken, K . E . H . , and K . Martin. 2004. Nest cavity availability and selection in aspen-conifer groves in a grassland landscape.. Canadian Journal of Forest Research 34: 2099-2109. Aitken, K . E . H . , K . L . Wiebe, and K . Martin. 2002. Nest site reuse patterns for a cavity-nesting bird community in interior British Columbia. A u k 119: 391-402. Ajayi , S. S. 1977. Field observations on the African Giant Rat Cricetomys gambianus in Southern Nigeria. East African Wildlife Journal 15: 191-198. Albano, D . J. 1992. Nesting mortality of Carolina Chickadees breeding in natural cavities. Condor 94: 371-382. Angelstam, P., and G . Mikusinski . 1994. Woodpecker assemblages in natural and managed boreal and hemiboreal forest: a review. Annales Zoologici Fennici 31: 157-172. Aubry, K . B . , and C. M . Raley. 2002. The pileated woodpecker as a keystone habitat modifier in the Pacific Northwest. In Proceedings of the Symposium on the Ecology and Management of Dead Wood in Western Forests, Reno, N V , November 2-4, 1999, W F Laudenslayer Jr., P J Shea, B E Valentine, C P Weatherspoon, and T E Lisle, Eds. General Technical Report PSW-GTR-181 , Pacific Southwest Research Station, United States Forest Service, U S Department of Agriculture, Albany, C A . Batra, S. W . T. 1979. Nests of the Eumenid wasp Anterhynchium abdominal bengalense from a termite mound in India. Oriental Insects 13: 163-166. 12 Bock, C. E . , and D . C. Fleck. 1995. Avian response to nest box addition in two forests of the Colorado Front Range. Journal of Field Ornithology 6 6 : 352-362. Brightsmith, D . J. 2000. Use of arboreal termitaria by nesting birds in the Peruvian Amazon. Condor 1 0 2 : 529-538. Biirt, W . H . , and R. P. Grossenheider. 1980. A field guide to the mammals: North America north of Mexico, 3 r d ed. Houghton Mif f l in Company, Boston, M A . Carlson, A . , U . Sandstrom, and K . Olsson. 1998. Availabili ty and use of natural tree holes by cavity nesting birds in a Swedish deciduous forest. Ardea 8 6 : 109-119. Clark, T. W. , T. M . Campbell III, D . G . Socha, and D. E . Casey. 1982. Prairie-dog colony attributes and associated vertebrate species. Great Basin Naturalist 4 2 : 572-582. Conner, R. N . , D . Saenz, and D . C. Rudolph. 2004. The red-cockaded woodpecker: interactions with fire, snags, fungi, rat snakes and pileated woodpeckers. Texas Journal of Science 5 6 : 415-426. Cuervo, J. J. 2004. Nest-site selection and characteristics in a mixed-species colony of Avocets Recurvirostra avosetta and Black-winged stilts Himantopus himantopus. B i rd Study 5 1 : 20-24. Daily, G . C , P. R. Ehrlich, and N . M . Haddad. 1993. Double keystone bird in a keystone species complex. Proceedings of the National Academy of Science U S A 9 0 : 592-594. DeLong, S. C , S. A . Fall , and G . D . Sutherland. 2004. Estimating the impacts of harvest distribution on road-building and snag abundance. Canadian Journal of Forest Research 3 4 : 323-331. Desmond, M . J., and J. A . Savidge. 1996. Factors influencing Burrowing O w l (Speotyto cunicularid) nest densities and numbers in western Nebraska. American Midland Naturalist 1 3 6 : 143-148. 13 Duncan, S. 2003. Coming home to roost: the pileated woodpecker as ecosystem engineer. Science Findings, No . 57. U S D A Pacific Northwest Research Station, Portland, OR. Eggers, S., M . Griesser, M . Nystrand, and J. Ekman. 2006. Predation risk induces changes in nest-site selection and clutch size in the Siberian jay. Proceedings of the Royal Society B -Biological Sciences 273: 701-706. Ehrlich, P. R., and G . C. Daily. 1988. Red-naped sapsuckers feeding at willows: possible keystone herbivores. American Birds 42: 357-365. Ehrlich, P. R., D . S. Dobkin, and D . Wheye. 1988. The birders' handbook: a field guide to the natural history of North American birds. Simon and Schuster Inc., New York, N Y . Forstmeier, W. , and I. Weiss. 2004. Adaptive plasticity in nest-site selection in response to changing predation risk. Oikos 104: 487-499. Hazlett, B . A . 1981. The behavioural ecology of hermit crabs. Annual Review of Ecology and Systematics 12: 1-22. Jones, C. G . , J. H . Lawton, and M . Shachak. 1994. Organisms as ecosystem engineers. Oikos 69:373-386. Jones, C. G . , J. H . Lawton, and M . Shachak. 1997. Positive and negative effects of organisms as physical ecosystem engineers. Ecology 78: 1946-1957. Kesler, D . C , and S. M . Haig. 2005. Selection of arboreal termitaria for nesting by cooperatively breeding Micronesian kingfishers Todiramphus cinnamominus reichenbachii. Ibis 147: 188-196. Lindenmayer, D . B . , R. B . Cunningham, M . . T . Tanton, A . P. Smith, and H . A . N i x . 1991. Characteristics of hollow-bearing trees occupied by arboreal marsupials in the montane ash forests of. the central highlands of Victoria, Southeast Australia. Forest Ecology and Management 40: 289-308. 14 Magnusson, W . E . , A . P. Lima, and R. M . Sampaio. 1985. Sources of heat for nests of Paleosuchus trigonatus and a review of crocodilian nest temperatures. Journal of Herpetology 19: 199-207. Martin, K . , and J. M . Eadie. 1999. Nest webs: a community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management 115: 243-257. Martin, K . , K . E . H . Aitken, and K . L . Wiebe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. Condor 106: 5-19. McCal lum, D. A . , F. B . G i l l , and S. L . L . Gaunt. 2001. Community assembly patterns of parids along an elevational gradient in western China. Wilson Bulletin 113: 53-64. Mikusinski , G . , and P. Angelstam. 1998. Economic geography, forest distribution, and woodpecker diversity in central Europe. Conservation Biology 12: 200-208. Mikusinski , G . , M . Gromadzki, and P. Chylarecki. 2001. Woodpeckers as indicators of forest bird diversity. Conservation Biology 15: 208-217. Newman, D . G . 1987. Burrow use and population densities of Tuatara Sphenodon punctatus and how they are influenced by Fairy Prions Pachyptila turtur on Stephens Island, New Zealand. Herpetologica 43: 336-344. Newton, I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biological Conservation 70: 265-276. Palmer, T. M . 2003. Spatial habitat heterogeneity influences competition and coexistence in an African acacia ant guild. Ecology 84: 2843-2855. Pimm, S. L . , and J. W . Pimm. 1982. Resource use, competition, and resource availability in Hawaiian honeycreepers. Ecology 63: 1468-1480. 15 Raphael, M . G., and M . White. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada (California, USA). Wildlife Monographs, No. 86. The Wildlife Society, Bethesda, MD. Remm, J., A. Lohmus, and K. Remm. 2006. Tree cavities in riverine forests: what determines their occurrence and use by hole-nesting passerines? Forest Ecology and Management 221: 267-277. Scott, V. E. 1979. Bird response to snag removal in ponderosa pine. Journal of Forestry 77: 26-28. SPSS Inc. 2002. SPSS, version 11.5.0. SPSS Inc. Chicago, IL. Steeger, C , and C. L. Hitchcock. 1998. Influence of forest structure and disease on nest-site selection by Red-breasted Nuthatches. Journal of Wildlife Management 62: 1349-1358. Thomas, J. W., R. G. Anderson, C. Maser, and E. L. Bull. 1979. Snags. In: Wildlife habitats in managed forests: the Blue Mountains of Oregon and Washington. U.S. Dept. of Agriculture Forest Service, Agriculture Handbook No. 553. Washington, D.C. Van Balen, J. H., C. J. H. Booy, J. A. Van Franeker, and E. R. Osieck. 1982. Studies on hole-nesting birds in natural nest sites: 1. Availability and occupation of natural nest sites. Ardea 70: 1-24. Vance, R. R. 1972. Competition and mechanism of coexistence in three sympatric species of intertidal hermit crabs. Ecology 53: 1062-1074. Weaver, C. M . 1982. Breeding habitats and status of the Golden-shouldered Parrot Psephotus chrysopterygius in Queensland, Australia. Emu 82: 2-6. Wesolowski, T. 1989. Nest-sites of hole nesters in a primaeval temperate forest, Bialowieza National Park, Poland. Acta Ornithologica 25: 321-351. Wiebe, K. L., W. D. Koenig, and K. Martin. 2007. Costs and benefits of nest reuse versus excavation in cavity-nesting birds. Annales Zoologici Fennici 4 4 : in press. 16 C H A P T E R 2: T H E I M P O R T A N C E O F E X C A V A T O R S I N C A V I T Y - N E S T I N G C O M M U N I T I E S : A V A I L A B I L I T Y A N D U S E O F N A T U R A L T R E E C A V I T I E S I N O L D M I X E D F O R E S T S O F W E S T E R N C A N A D A . 1 INTRODUCTION A broad range of bird, mammal, reptile, amphibian, and insect species worldwide use cavities in trees for nesting, roosting, food storage, and cover, including over 100 bird and mammal species in North America (Burt and Grossenheider 1980, Newton 1998). Tree cavities provide secure sites from predators and inclement weather, and their availability and distribution are considered to shape life history traits and community structure for the group (Martin 1993, Martin et al. 2004, Wiebe et al. 2006). Excavators such as woodpeckers create cavities in dying or dead wood. Non-excavated cavities may originate from broken tree limbs, crevices behind bark, hollow stumps, wound openings and a range of fungal and other decay processes. Cavities may remain in the landscape for several years to decades, providing a required nesting resource for non-excavating secondary cavity-nesters, and an option for excavators to reuse existing cavities (Aitken et al. 2002, Wiebe et al. 2006). Woodpeckers are considered to be keystone species in many systems because, by providing nest-sites for secondary cavity-nesters, they may influence the abundance and distribution of other species in the community (Daily et al. 1993, Martin and Eadie 1999). However, in some systems non-excavated cavities may be plentiful enough that excavated cavities are used relatively infrequently or are avoided by secondary cavity-nesters (Carlson et al. 1998, Remm et al. 2006, Wesolowski, in review). Non-excavated cavities may also be less susceptible to predation by large woodpecker species than excavated cavities (Walankiewicz ' A version of this chapter has been accepted for publication. Aitken, K. E. H., and K. Martin. 2007. The importance of excavators in hole nesting communities: availability and use of natural tree holes in old mixed forests of western Canada. Journal of Ornithology. (In press, August 2007). 17 2002, Wesolowski 2002). However, few studies have examined differences between excavated and non-excavated cavities. In many studies of nest-site selection, cavity origin is not recorded. Comparing use and availability of excavated and non-excavated cavities may provide insight into the importance of woodpeckers as keystone species, and into the nest-site requirements of secondary cavity-nesters when they are released from the constraints of woodpecker nest-site preferences and, potentially, competition for excavated cavities. The cavity-nesting bird and mammal community of Interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests of central British Columbia, Canada is one of the richest in North America (Martin and Eadie 1999). Approximately 22% of the bird species in the region are cavity-nesters and both excavators and non-excavators use non-excavated cavities (Martin and Eadie 1999, Aitken and Martin 2004). In this paper, I examine use of excavated and non-excavated cavities by excavators and secondary cavity-nesters, and compare characteristics of excavated and non-excavated cavities used for nesting at the community level, and by several individual species. I also consider cavity type in relation to forest context, and present the results of a survey of availability of excavated and non-excavated cavities. METHODS Study Area Nest cavities were located and monitored on a total of 15 study sites at Riske Creek between 1995-2006, eleven of which were mature coniferous forest (Doc English Lake, Hermit H i l l , Little T i l l Lake 1, Little T i l l Lake 2, Maclntyre Lake, Mili tary Gate, Rock Lake, Solitary Woods, Sword Pine, Tongue, The Y ; Figure 1.2), and four of which were complexes of aspen groves (Rock Complex, Rock Pine, Sora Complex, Sword Creek). A n additional 12 coniferous forest study sites were monitored near 150 M i l e House, B C , approximately 60 km southeast of Riske Creek. 18 Nest location and monitoring From 1 M a y to 31 July 1995-2006, all sites were searched for occupied cavity nests. In my study area, most migratory and resident cavity nesters did not begin nesting until the first or second week of May. Systematic nest searches were conducted across all sites for an average of 6-7 observer-hours of nest searching per sampling site per week. Because cavity nesters reused cavities and nest trees in multiple years (Aitken et al. 2002), existing cavities were checked (both previously used and those not known to be occupied in previous years), as well as newly excavated cavities. Occupied cavities were located by looking or listening for excavation, by tapping or scraping at the base of trees containing cavities to detect occupants, and by observing breeding birds or hearing begging nestlings. Finding occupied nests was facilitated by detecting general locations of cavity nesters during early morning point-count surveys. Cavities within reach of a ladder (< 5.2m) were inspected visually with flashlights and mirrors. In 2005 and 2006, a TreeTop Peeper™ camera system (Sandpiper Technologies, Manteca, C A , U S A ) was used to monitor cavities up to 17 m, and in trees too unstable to reach with a ladder. Nests were considered occupied i f they contained at least one egg or nestling. I also monitored cavities occupied by cavity-nesting mammals such as red squirrel (Tamiasciurus hudsonicus), northern flying squirrel (Glaucomys sabrinus), and bushy-tailed woodrat (Neotoma cinered), as well as use by facultative .cavity users such as deer mouse (Peromyscus maniculatus), short-tailed weasel (Mustela erminea), fisher (Martes pennanti), and chipmunk (Eutamias spp.). Occupied cavities were assigned unique numbers and nest trees were marked with numbered aluminum tags to facilitate relocation across the study years. 19 Nest tree and cavity characteristics After nest cavities were vacated, I recorded tree and cavity variables. Cavity origin was categorized as excavated or non-excavated. Because non-excavated cavities were located in broken branch nodes, behind bark, tops of stumps, etc., these were clearly distinguishable from excavated holes. The species of the cavity excavator was recorded i f observed during excavation, or occasionally from diagnostic features such as entrance size and shape. Tree characteristics included species, decay stage (live or dead); and diameter at breast height (DBH) . Cavity variables included height above ground (m), vertical depth (cm), internal diameter (cm), entrance height and width (cm), and orientation. Vertical depth was measured from the bottom of the cavity entrance to the floor of the cavity. Internal diameter was measured from the inner edge of the lower lip of the entrance to the back wall of the cavity. Entrance area (cm 2) was calculated using entrance height and width and the formula for the area of an ellipse. Distance to nearest forest edge (grassland, pond, or stream) was recorded either directly using 30 m measuring tapes or by global positioning system (GPS). Availability of excavated and non-excavated cavities In 2000,1 surveyed cavity availability in 5 coniferous forest sites, and in 35 aspen groves (0.05 -3 ha). A t each coniferous forest site, I established 3 transect lines, 100 m apart, starting at the forest edge and extending 350 m into the forest. Walking along each transect, I recorded all cavities within 10 m on either side of the line. In each aspen grove, I searched throughout the entire patch, recording all cavities. The same two observers surveyed each site to ensure that cavity-searching techniques were consistent among sites. I did not include partially excavated trial cavities in my surveys, or cavities with a vertical depth of <1 cm. I recorded tree and cavity characteristics as described above for nest cavities. 20 Data analyses I used linear mixed effects ( L M E ) models to determine whether tree and cavity characteristics differed among nests in excavated and non-excavated cavities. Nest-site variables examined were height above ground, vertical depth, internal diameter, entrance area, tree D B H , and distance from grove or forest edge.. Data were analyzed using the procedure L M E in the statistical program R (R version 2.4.0, R Development Core Team 2006). I built separate models for each nest-site variable. Each model included the dependent variable of interest (e.g. height above ground) and cavity type (excavated or non-excavated) as the fixed effect. Because cavities were used multiple times across years, I included individual cavity as a random effect in each model. Distance to edge followed a Poisson distribution in coniferous forest sites; thus, I used generalized linear mixed models with a penalized quasi-likelihood method of parameter estimation (glmmPQL; Breslow and Clayton 1993, Nelson and Leroux 2006) to compare distance to edge among excavated and non-excavated cavities in those sites. P Q L is an approximate method of inference in G L M M s in which maximum likelihood methods are not appropriate due to the distribution of random effects (Wedderburn 1974,- Breslow 2003). Independent samples /-tests were used to compare characteristics of excavated and non-excavated cavities recorded in my 2000 cavity availability survey. Where necessary, data were log- or square-root transformed in order to meet assumptions of normality and equality of variance. Where data could not be transformed to meet assumptions, non-parametric Mann-Whitney [/-tests were used. I tested whether orientation of excavated and non-excavated cavity entrances was random or non-random using one-sample Watson's U 2 tests for circular distributions, and mean orientation of excavated and non-excavated cavities were compared using two-sample Watson's U 2 test in the statistical program Oriana (Oriana version 2.0.2, Kovach Computing Services 2005). Chi-square tests were used to compare proportions of 21 excavated and non-excavated cavities in coniferous forests versus aspen groves, and in live versus dead trees. RESULTS Excavated versus non-excavated cavities used for nesting I was able to identify mode of creation (excavated or non-excavated) for 1371 individual cavities used for nesting in 1057 trees on my study sites between 1995-2006. Ninety-five percent of these cavities were excavated and 5% were non-excavated. Red-naped sapsucker (Sphyrapicus nuchalis) and northern flicker excavated 52% of all cavities, 19% were excavated by other woodpecker species, and 11% were excavated by chickadees or red-breasted nuthatch (Sitta canadensis; Table 2.1). Among non-excavated cavities, most were in broken branch nodes, crevices behind loose bark, and hollow stumps ("chimneys"). Two unusual mountain bluebird nests (one wedged in a cracked boulder, the other in the hollow end of a metal bridge piece) were not included in my analyses of non-excavated cavities. I monitored 2728 nesting'attempts, 94% of which were in excavated cavities, and 6% in non-excavated cavities. A s expected, the proportion of nests in non-excavated cavities differed among excavators and secondary cavity-nesters, with 10% of secondary cavity-nester nests in non-excavated cavities, and just 2% of excavator nests in non-excavated cavities. While northern flicker was the only woodpecker that used both excavated and non-excavated cavities, only 4% of flicker nests were in non-excavated holes (Table 2.1). The only species that used non-excavated cavities more than 20% of the time was the bushy-tailed woodrat (Neotoma cinerea; Table 2.1). Wi th all species grouped together, nests in excavated cavities were on average almost two meters higher above ground than nests in non-excavated cavities (Figure 2.1a, Table 2.2). Excavated cavities used for nesting were significantly narrower internally (Figure 2.1c), and had 22 smaller entrances than non-excavated cavities (Figure 2.Id, Table 2.2). Vertical cavity depth and tree diameter at breast height did not differ among excavated and non-excavated cavities used for nesting when all species were grouped (Figures 2.1b and e, Table 2.2). While there was little difference in distance to nearest edge among nests in excavated and non-excavated cavities in aspen groves, nests in excavated cavities in coniferous forest were farther from edge than were those in non-excavated cavities (Figure 2.2). However, this was not significant in my mixed model analysis (Table 2.2). Orientations of excavated and non-excavated cavities were non-random, with more cavities facing southwest than other directions (Watson's one-sample U2 test; excavated cavities: p = 211° ± 100°, U2 = 3.1, N = 1289, P < 0.005; non-excavated cavities: p. = 203° ± 99°, U2 = 0.2, N = 64, P < 0.05; Figure 2.3). Mean orientation did not differ between excavated and non-excavated cavities (Watson's two-sample U2 test: U2 = 0.07, P > 0.05, N =' 1289,64). Five species had large enough sample sizes to allow me to compare characteristics of nests in excavated and non-excavated cavities: northern flicker, mountain chickadee, mountain bluebird, European starling, and tree swallow. Northern flicker nests in excavated cavities were significantly higher above ground and shallower than non-excavated cavities (Figure 2.1, Table 2.2). Mountain chickadee nests in excavated cavities were significantly shallower than non-excavated cavities (Figure 2.1, Table 2.2). In coniferous forests, mountain chickadee nests in excavated cavities were significantly farther from edge than were nests in non-excavated cavities (Figure 2.2, Table 2.2). This trend was reversed in aspen groves, where mountain chickadee nests in non-excavated cavities were more than twice as far from edge as were excavated cavities (Figure 2.2, Table 2.2). O f the five species examined, only mountain chickadees nested in both excavated and non-excavated cavities in coniferous forest sites (Figure 2.2). Mountain bluebird nests in excavated cavities were significantly higher above ground, had considerably smaller entrances, and were in smaller trees than were non-excavated cavities (Figure 2.1, Table 2.2). 23 There were few differences between excavated and non-excavated cavities used by European starling, although entrance areas of excavated starling nests were significantly larger than those of non-excavated cavities (Figure 2.1, Table 2.2). Tree swallow nests in excavated cavities were significantly higher above ground, narrower internally and had smaller entrances than did nests in non-excavated cavities (Figure 2.1, Table 2.2). A v a i l a b i l i t y of excava ted versus non-excavated cavi t ies In 2000,1 surveyed 200 available cavities, of which 85% were excavated and 15% were rion-excavated. Mean density of excavated cavities was 11.2 per hectare, versus 1.1 per hectare for non-excavated cavities. Aspen groves had a slightly lower proportion of non-excavated cavities than coniferous forests (14% of 180 cavities in aspen groyes, 20% of 20 cavities in coniferous) but this difference was not significant (X2 = 0.44, df = 1, N = 200, P = 0.5). While non-excavated cavities were similar to excavated cavities in height above ground, internal diameter and distance to nearest edge, they tended to be deeper and have larger entrances, but not significantly so (Table 2.3). Trees with excavated cavities did not differ in stage of decay from those with non-excavated cavities (Live versus dead: X2 = 0.02, df = 1, N = 200, P = 0.9). DISCUSSION Both the availability and use of excavated and non-excavated cavities varies across forest types and ages, landscape types, and possibly across continents (Wesolowski, in review). Costs and benefits associated with cavity origin, and competitive abilities to secure a preferred cavity type, may vary among species. Here, I discuss the variation in abundance and use of the two major cavity types across species and in relation to forest type and context for northwestern North America. 24 Previous studies in forests of Europe and As ia reported a wide range in the relative abundance of excavated and non-excavated cavities. Remm et al. (2006) found that woodpeckers excavated 88% of cavities in deciduous forests in Estonia, while Carlson et al. (1998) found that 47% of cavities in Swedish deciduous forest were excavated. In contrast, in old-growth mixed forests in eastern Poland, non-excavated cavities were much more abundant than excavated cavities (11-11.5 vs 4.5-5 cavities/ha) and about 90% of secondary cavity-nesters nested in non-excavated cavities (Wesolowski, in review). In Mongolian mature forests, 75% of nesting attempts were in non-excavated cavities (Bai et al. 2003). On my study sites, excavated cavities were much more abundant (11.2 cavities/ha) than non-excavated cavities (1.1/ha). Woodpeckers were abundant in my region and individuals may excavate multiple cavities each year (Bonar 2000, Walters et al. 2002). Because these cavities are often excavated in live trees or those in the earliest stages of decay, these cavities may persist for several years to over 30 years (Aitken et al. 2002, Wesolowski, in review). If excavated cavities are created at a faster rate than non-excavated cavities or survive longer, this may lead to a greater supply of excavated cavities compared to non-excavated cavities in the landscape. While secondary cavity-nesters as a group used excavated and non-excavated cavities approximately in proportion to their availability in the landscape, use of non-excavated cavities varied among species. The larger secondary cavity-nester species, bufflehead (Bucephala albeola), Barrow's goldeneye (Bucephala islandica), American kestrel (Falco sparverius), and northern saw-whet owl (Aegolius acadicus) used non-excavated cavities less frequently than some of the smaller secondary cavity-nesters, such as bluebird and starling. Although non-excavated cavities tended to be larger on average than excavated cavities, these cavities were also relatively scarce. Therefore, large-bodied cavity-nesters may be constrained by the 25 availability of large cavities and rely primarily on those created by large excavators (Martin et al. 2004). There were ten excavating species in my study region, including 10-11 g chickadee and nuthatch, and eight species of woodpecker ranging in mass from the 30 g downy woodpecker (Picoides pubescens), to the 300 g pileated woodpecker (Dryocopus pileatus; Campbell et al. 1990, B u l l and Jackson 1995, Martin and Norris 2007). This excavator group provides cavities across a broad range of habitat types that accommodate an array of secondary cavity-nesters from 10 g chickadees to 1 kg Barrow's goldeneye and 2.5 kg fisher (Martin'et al. 2006). In European forests, woodpecker species diversity was positively correlated with secondary cavity-nester diversity, likely due to an increase in cavity diversity in stands with a variety of woodpeckers (Mikusinski and Angelstam 1998). Wi th a broad range of excavating species in the community and, thus, a wide variety of potential nest-sites available, secondary cavity-nesters may not be as dependent on non-excavated cavities as in systems in which the excavator assemblage has been altered. Three excavators, northern flicker, red-breasted nuthatch, and black-capped chickadee (Poecile atricapillus) used a small proportion of non-excavated cavities for nesting in my sites. Nuthatches and chickadees are weak excavators that require trees in advanced stages of decay for excavation, and may be limited by the availability of these trees (Dickson et al. 1983, Steeger and Hitchcock 1998). Naturally occurring cavities may provide ready-made nest-sites when suitable trees are unavailable for excavation'for these species. The only woodpecker to use non-excavated cavities in my study, northern flicker, experiences aggressive competition from European starlings, and is often evicted from its nest cavities (Moore 1995, Wiebe 2003). Use of non-excavated cavities may be a means to avoid competition from starlings and other secondary cavity-nesters, and may allow excavators to initiate breeding earlier (Wiebe et al. 2006). 26 Non-excavated cavities used for nesting tended to be larger internally and had larger entrances than excavated cavities. Both cavity entrance size and internal size have been linked with fecundity and reproductive success in cavity-nesters. Cavities with larger volume may allow for larger clutch sizes, better thermoregulation by nestlings, or better protection from predators (Alatalo et al. 1988, Slagsvold 1989, Wiebe and Swift 2001). Conversely, cavities with small entrances may restrict access by medium and large nest predators (Wesolowski 2002). Among species using non-excavated cavities, there may be a trade-off between the potential advantage of larger internal area and the potential disadvantage of larger entrance area. However, among species that use non-excavated cavities somewhat regularly (e.g., starlings, bluebirds), clutch size, hatch success and fledge success in non-excavated cavities all increased with increasing frequency of use of non-excavated cavities (Martin, unpublished data). For these species, the potential advantages of non-excavated cavities, such as reduced competition for nest-sites, and increased cavity volume, may outweigh any disadvantages. O f the five species examined in-depth, starlings selected excavated and non-excavated cavities for nesting that were the most similar to each other. Although starlings are considered to be nest-site generalists because they have adapted successfully to nesting in both natural and human-made structures, nest-site selection studies of starlings suggest that they are actually quite specialized in their nest-site preferences. In a nest-site selection study of cavity-nesters in Poland, starlings had stronger preferences for cavities based on tree species, height above ground, and cavity entrance shape than most other species in the community (Wesolowski 1989). Starlings in the Netherlands and Sweden preferred cavities that were large internally (van Bai en' et al. 1982, Carlson et al. 1998). In an earlier study, I found that starlings preferred nest-sites that were larger internally, closer to grassland edge, and in trees with only one cavity (Aitken and Martin 2004). In urban areas of Ontario, Canada, starlings used a smaller range of human-27 made structures for nesting and with a narrower range in characteristics than another introduced secondary cavity-nester, the house sparrow (Passer domesticus; Savard and Falls 1981). These strong nest site preferences may cause starling populations to be limited by the availability of suitable cavities. In an experiment in which I blocked the entrances of preferred nest cavities, the number of starling nests declined significantly and did not recover following reopening of cavities (Chapter 4). Starlings are successful competitors for nest-sites, either through direct interference with other cavity-nesters or indirectly through timing of breeding (Ingold 1994, 1996, Wiebe 2003, Fisher and Wiebe 2006), and thus may be better able to acquire higher quality non-excavated cavities than other less competitive or later nesting species. I observed an abundant supply of natural (excavated and non-excavated) cavities on my predominantly mature sites in British Columbia (12.3 cavities/ha), as did Wesolowski (in review) in old-growth temperate forest in eastern Poland (16 cavities/ha). Interestingly, in both studies, secondary cavity-nesters primarily used the more abundant cavity type (excavated holes in my study sites, non-excavated holes in Wesolowski's sites). In both studies, it appeared that cavity supply exceeded demand, with the majority of cavities unoccupied each year (Aitken et al. 2002, Aitken and Martin 2004, Wesolowski in review). Thus, in old forest systems, the role of several critical ecological and environmental factors such as food supply, predation and environmental conditions may be just as or more important than cavity availability in limiting cavity-nester densities (Walankiewicz 1991, Wesolowski and Stawarczyk 1991, Newton 1994, 1998, Lohmus and Remm 2005, Remm et al. 2006). 28 Table 2.1. Bi rd and mammal species nesting in excavated and non-excavated tree cavities, and percent of total cavities excavated by woodpecker and other excavator species in interior British Columbia, Canada, 1995-2006. See Table 1.2 for scientific names of species. % nests in % of % nests in non- cavities excavated excavated Total excavated Species cavities cavities nests (N=1371) Excavators Red-naped sapsucker. 100 0 372 31 Red-breasted sapsucker 100 0 2 1 Downy woodpecker 100 0 63 5 Hairy woodpecker 100 0 74 6 American three-toed woodpecker 100 0 56 4 Black-backed woodpecker 100 0 4 2 Northern flicker 96 4 407 21 Pileated woodpecker 100 0 31 3 Black-capped chickadee 87 13 38 2 Red-breasted nuthatch 96 4 243 9 Unknown excavator N A N A N A 13 Total Excavators 98 2 1290 Secondary cavity-nesting birds Wood duck 100 0 1 Bufflehead 97 3 58 Barrow's goldeneye 100 0 5 Hooded merganser 100 .0 1 American kestrel 95 5 42 Flammulated owl 100 0 1 Northern hawk owl 0 100 2 Northern saw-whet owl 100 0 17 Tree swallow 91 9 307 Mountain chickadee 93 7 295 l a Mountain bluebird 86 14 253 European starling 89 11 341 Unidentified secondary cavity-nester 67 33 3 Total secondary cavity-nester 90 10 1326 Small mammals Northern flying squirrel 86 14 14 Chipmunk 0 100 2 Red squirrel 90 10 81 . Bushy-tailed woodrat, 67 33 6 Deer mouse 100 , 0 1 Fisher 100 0 1 Short-tailed weasel (ermine) 100 0 1 29 Table 2.1, cont'd Species % nests in % nests in non-excavated excavated cavities cavities Total nests % of cavities excavated (N=1371) Unidentified small mammal Total small mammals Bark nesters Brown creeper Certhia americana 100 87 0 0 13 100 2 108 a Two cavities were excavated by mountain chickadee, which we classify as a secondary cavity-nester as per H i l l and Lein (1988) 30 Table 2.2. Linear mixed effects models predicting nest-site characteristics of cavity-nesting birds and mammals in interior British Columbia, Canada, between 1995-2006. Separate models were built for each of six nest-site characteristics, with cavity type ("excavated", "non-excavated") as the fixed effect, and individual cavity as the random effect. A positive estimate indicates that excavated cavities had a higher mean value than non-excavated cavities, and vice versa for negative estimates. Confidence intervals that do not encompass zero are highlighted in bold.. See Table 1.2 for species scientific names. Species Estimate (Excavated vs non-excavated) SE df 95% Confidence int -0.61 0.08 1364 (-0.77 - -0.45) 0.23 0.20 664 (-0.16-0.62) . 0.22 0.06 702 (0.10 - 0.34) 0.51 0.10 709 (0.31 - 0.71) 0.003 0.01 1653 (-0.02 - 0.03) -0.15 0.27 438 (-0.68-0.38) 0.005 0.49 704 (-0.96 - 0.97) -0.52 0.24 239 (-0.99 - -0.05) 0.30 0.13 155 (0.05 - 0.55) -0.08 0.08 160 (-0.24-0.08) -0.01 0.10 159 (-0.21-0.19) -0.08 0.10 237 (-0.28-0.12) 0.26 0.61 139 (-0.94- 1.46) 0.32 0.93 186 (-1.50-2.14) 3.89 1.67 88 (0.62-7.16) -0.12 0.17 99 (-0.45-0.21) 0.04 0.22 100 (-0.39-0.47) -1.04 2.30 184 (-5.55-3.47) 24.0 8.37 23 (7.59-40.4) -1.55 0.78 124 (-3.08 - -0.02) a) All species Cavity ht above ground (m) a Vertical depth (cm) a Internal diameter (cm) b Entrance area (cm ) Tree diameter at breast ht (cm) b Distance to nearest edge (aspen groves) a , Distance to nearest edge (coniferous forest) b) Northern flicker Cavity ht above ground (m) b Vertical depth (cm) b Internal diameter (cm) b Entrance area ( c m 2 ) b Tree diameter at breast ht (cm) b Distance to nearest edge (aspen groves) a c) Mountain chickadee Cavity ht above ground (m) Vertical depth (cm) Internal diameter ( cm) b Entrance'area ( c m 2 ) b Tree diameter at breast ht (cm) b Distance to nearest edge (aspen groves) Distance to nearest edge (coniferous forest) 31 Table 2.2, cont'd Estimate ' (Excavated vs non-Species excavated) SE df 95% Confidence interval d) Mountain bluebird Cavity ht above ground (m) -1.64 0.65 140 (-2.91 - -0.37) Vertical depth ( c m ) a 0.42 0.40 101 (-0.36- 1.20) Internal diameter (cm) 1.48 1.03 108 (-0.54- 3.50) Entrance area ( c m 2 ) b 0.34 0.18 111 . (-0.01 - 0.69) Tree diameter at breast ht (cm) b 0.20 0.09 137 (0.02 - 0.38) Distance to nearest edge (aspen 0.02 0.48 100 (-0.92 - 0.96) groves) a e) European starling Cavity ht above ground (m) b -0.24 0.20 131 (-0.63--0.15) Vertical depth (cm) b -0.14 0.11 90 (-0.36--0.08) Internal diameter (cm) b 0.15 0.10 93 (-0.05 ^ -0.35) Entrance area ( c m 2 ) b -0.37 0.12 93 (-0.61 - -0.13) Tree diameter at breast ht (cm) b 0.007 0.09 131 (-0.17--0.18) Distance to nearest edge (aspen 1.24 2.72 108 (-4.09 --6.57) groves) f) Tree swallow Cavity ht above ground ( m ) b -0.31 0.15 201 (-0.60 - -0.02) Vertical depth ( c m ) a 0.49 N 0.32 118 (-0.14- -1.12) Internal diameter (cm) b 0.20 0.09 128 (0.02 - 0.38) Entrance area ( c m 2 ) b ' 0.55 0.16 128 (0.24 - 0.86) Tree diameter at breast ht ( cm) b 0.12 0.07 199 (-0.02 -- 0.26) Distance to nearest edge (aspen 0.07 0.46 122 (-0.83 -- 0.97) groves) b a Square-root transformed data used in analysis b Log-transformed data used in analysis 32 Table 2.3. Characteristics of available excavated and non-excavated cavities surveyed in coniferous forests and aspen groves in 2000. E x c a v a t e d N o n - e x c a v a t e d Tes t V a r i a b l e M e a n ± S E M e a n ± S E s t a t i s t i c 3 df P Cavity ht above ground (m) 2.7 ± 0 . 1 ' 2.7 ± 0 . 2 -0.29 198 0.8 Vertical depth (cm) b 24.4 ± 1.8 31.8 ± 6 . 9 -1.29 172 0.2 Internal diameter (cm) 13.2 ± 0 . 4 12.8 ± 1 . 1 0.40 180 0.7 Entrance area (cm 2 ) c 25.2 ± 1.0. 38.2 ± 7 . 4 -1.20 178 0.2 Diameter at breast height (cm) b 34.2 ± 0.9 33.5 ± 3 . 1 1.30 197 0.2 Nearest edge (m) 25.7 ± 4 . 2 22.0 ± 7.4 2520.5 198 0.9 a Mann-Whitney U for nearest edge; Independent samples t for all others b Log-transformed data used in analysis 0 Square-root transformed data used in analysis 33 TRES EUST M O B L M O C H N O F L Total nests a) Cavity height above ground (m) 278 28 37 303 ^ V e r t i c a l depth (cm) • Excavated _Li9 19 180 28 Non-excavated ^ 218 275 20 ^ 392 H 2549" 174 0.0 2.0 4.0 Mean.+/- SE c) Internal diameter (cm) TRES EUST M O B L M O C H N O F L Total nests ^ J J 2 _ 21 — m 190 28 TH 182 6.0 0.0 20.0 40.0 Mean +/- SE d) Entrance area (sq-cm) 175 20 192 60.0 26 144 —m 266 13 115 0.0 5.0 10.0 15.0. 20.0 25.0 0.0 20.0 40.0 60.0 80.0 100.0 Mean +/- SE e) Diameter at breast height (cm) Mean +/- SE 35 TRES • M H M U ^ 2 EUST mmmmmmmmmmmmmlh20i M O B L ^ ^ ^ ^ ^ ^ ^ ^ ^ • K M O C H K i l l H I P % r ] N O F L ^ ^ ^ ^ ^ ^ ^ ^ B ^ 3 3 9 0 ^ , > 2530 Total nests ^ ^ ^ ^ ^ H H ^ ^ ^ ^ ^ H - * 169 1 r 1 : — i 1 0.0 10.0 20.0 30.0 • 40.0 50.0 Mean +/- SE Figure 2.1. Characteristics of excavated and non-excavated cavities used by all species ("Total nests"), and by five individual species. See Table 1.2 for full species names, and Table 2.2 for results of mixed models analyses. 34 35.0 30.0 25.0 a) Aspen groves • Excavated • Non-excavated 2 w 20.0 <u oo =1 + 15.0 T3 2 w B + 10.0 5.0 0.0 60.0 50.0 40.0 i 30.0 20.0 10.0 0.0 b) Coniferous forest 184 99 28 12 r E - i 73 Total nests NOFL M O C H M O B L EUST TRES Figure 2.2. Distance of nests in excavated and non-excavated cavities to nearest edge in aspen groves and in coniferous forest sites. See Table 1.2 for full species names, and Table 2.2 for results of mixed models analyses. 35 a) Excavated cavities North West East South b) Non-excavated cavities West East South Figure 2.3. Orientation of a) excavated and b) non-excavated cavities. The arrow indicates mean orientation and the arcs to either side indicate the 95% confidence interval. See text for results of statistical tests. 36 REFERENCES Aitken, K . E . H . , and K . Martin. 2004. Nest cavity availability and selection in aspen-conifer groves in a grassland landscape. Canadian Journal of Forest Research 34: 2099-2109. Aitken, K . E . H . , K . L . Wiebe, and K . Martin. 2002. Nest-site reuse patterns for a cavity-nesting bird community in interior British Columbia. A u k 119: 391-402. Alatalo, R . V . , A . Carlson, and A . Lundberg. 1988. Nest cavity size and clutch size of pied flycatchers Ficedula hypoleuca breeding in natural tree-holes. Ornis Scandinavica 19: 317-319. Bai , M . - L . , F. Wichmann, and M . Muhlenberg: 2003. The abundance of tree holes and their utilization by hole-nesting birds in a primeval boreal forest of Mongolia. Acta Ornithologica 38:95-102 Bonar, R . L . 2000. Availabili ty of pileated woodpecker cavities and use by other species. Journal of Wildlife Management 64: 52-59. Breslow, N . E . 2003. Whither P Q L ? University of Washington Biostatistics Working Paper Series No. 192, University of Washington, Seattle, W A . Breslow, N . E . , and D . G . Clayton. 1993. Approximate inference in generalized linear mixed models. Journal of the American Statistical Association 88: 9-25. B u l l , E . L . , and J. E . Jackson. 1995. Pileated woodpecker (Dryocopuspileatus). In A . Poole, and F. G i l l , Eds. The Birds of North America, No . 148. The Academy of Natural Sciences, Philadelphia, P A , and The American Ornithologists' Union, Washington, D . C . Burt, W . H . , and R. P. Grossenheider. 1980. A Field Guide to the Mammals: North America North of Mexico, 3 r d ed. Houghton Mif f l in Company, Boston, M A . Campbell, R. W. , N . K . Dawe, I. McTaggart-Cowan, J. M . Cooper, G . W . Kaiser, and M . C. E . M c N a l l . 1990. The Birds of British Columbia, Volume 2: nonpasserines - diurnal birds of 37 prey through woodpeckers. Royal British Columbia Museum, Victoria and Canadian Wildlife Service, Delta. Carlson, A . , U . Sandstrom, and K . Olsson. 1998. Availabil i ty and use of natural tree holes by cavity nesting birds in a Swedish deciduous forest. Ardea 8 6 : 109-119. Daily, G . C , P. R. Ehrlich, and N . M . Haddad. 1993. Double keystone bird in a keystone species complex. Proceedings of the National Academy of Sciences, Washington, D C , U S A 90:592-594. Dickson, J. G . , R. N . Conner, and J. H . Williamson. 1983. Snag retention increases bird use of a clear-cut. Journal of Wildlife Management 4 7 : 799-804. Fisher, R., and K . Wiebe. 2006. Nest site attributes and temporal patterns of northern flicker nest loss: effects of predation and competition. Oecologia 1 4 7 : 744-753. H i l l , B . G . , and M . R. Lein. 1988. Ecological relations of sympatric black-capped and mountain chickadees in southwestern Alberta. Condor 9 0 : 875-884. Ingold, D . J. 1994. Influence of nest-site competition between European starlings and woodpeckers. Wilson Bulletin 1 0 6 : 227-241. Ingold, D . J. 1996. Delayed nesting decreases reproductive success in Northern Flickers: implications for competition with European starlings. Journal of Field Ornithology 6 7 : 321-326. Kovach Computing Services. 2005. Oriana for Windows, Version 2.0.2. Anglesey, Wales. Lohmus, A . , and J. Remm. 2005. Nest quality limits the number.of hole-nesting passerines in their natural cavity-rich habitat. Acta Oecologica 2 7 : 125-128. Martin, K . , and J. M . Eadie. 1999/ Nest webs: a community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management 1 1 5 : 243-257. 38 Martin, K . , K . E . H . Aitken, and K . L . Wiebe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. Condor 106: 5-19. Martin, K . , A . Norris, and M . Drever. 2006. Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: implications for critical habitat management. B C Journal of Ecosystems and Management 7: 10-24. Martin, K . , and A . R. Norris. 2007. Life in the small-bodied cavity-nester guild: Demography of . sympatric Mountain and Black-capped Chickadees within Nest Web communities under chang habitat conditions. Chapter 8, In K.Otter, Ed. The Ecology and Behavior of Chickadees and Titmice: A n integrated approach, Oxford University Press. Oxford, Pp. 111-130. Martin, T. E . 1993. Evolutionary determinants of clutch size in cavity-nesting birds: nest predation or limited breeding opportunities. American Naturalist 142: 937-946. Mikusinski , G . and P. Angelstam. 1998. Economic geography, forest distribution, and woodpecker diversity in central Europe. Conservation Biology 12: 200-208. Moore, W . S. 1995. Northern flicker (Colapies auratus). In The Birds of North America, No. 166, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D . C . Nelson, K . P., and B . G . Leroux. 2006. Statistical models for autocorrelated count data. Statistics in Medicine 25: 1413-1430. Newton, I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biological Conservation 70: 265-276. Newton, I. 1998. Population limitation in birds. Academic Press, San Diego, C A . R Development Core Team. 2006. R: A language and environment for statistical computing. R Foundation for Statistical Computing^ Vienna, Austria. 39 Remm, J., A . Lohmus, and K . Remm. 2006. Tree cavities in riverine forests: what determines their occurrence and use by hole-nesting passerines? Forest Ecology and Management 221: 267-277. Savard, J.-P. L . , and J. B . Falls. 1981. Influence of habitat structure on the nesting height of birds in urban areas. Canadian Journal of Zoology 59: 924-932. Slagsvold, T. 1989. On the evolution of clutch size and nest size in passerine birds. Oecologia 79: 300-305. Steeger, C , and C. L . Hitchcock. 1998. Influence of forest structure and disease on nest-site selection by Red-breasted Nuthatches. Journal of Wildlife Management 62: 1349-1358. Van Balen, J. H . , C. J. H . Booy, J. A . van Franeker, and E . R. Osieck. 1982. Studies on hole-nesting birds in natural nest sites: 1. Availabili ty and occupation of natural nest sites. Ardea 70: 1-24. Walankiewicz, W . 1991. Do secondary cavity-nesting birds suffer more from competition for cavities or from predation in a primeval deciduous forest? Natural Areas Journal 11: 203-• 212. Walankiewicz, W . 2002. Nest predation as a limiting factor to the breeding population size of the Collared Flycatcher Ficedula albicollis in the Bialowieza National Park (NE Poland). Acta Ornithologica 37:91-106 Walters, E . L . , E . H . Mil ler , and P. E . Lowther. 2002. Red-breasted sapsucker (Sphyrapicus rubber)/Red-napQd sapsucker (Sphyrapicus nuchalis). In The Birds of North America, No. 663, A . Poole and F. G i l l , Eds. The Birds of North America, Inc., Philadelphia, P A . Wedderburn, R. W . M . 1974. Quasi-likelihood functions, generalized linear models, and the Gauss-Newton method. Biometrika 61: 439-447. Wesolowski, T. 1989. Nest-sites of hole nesters in a primaeval temperate forest, Bialowieza National Park, Poland. Acta Ornithologica 25: 321-351. 40 Wesolowski, T. 2002. Antipredator adaptations in nesting marsh tits Parus palustris - the role of nest site security. Ibis 144:593-601 Wesolowski, T. and T. Stawarczyk. 1991. Survival and population dynamics of nuthatches Sitta europaea breeding in natural cavities in a primeval temperate forest. Ornis Scandinavica 22: 143-154. Wiebe, K . L . 2003. Delayed timing as a strategy to avoid nest-site competition: testing a model using data from starlings and flickers. Oikos 100: 291-298. Wiebe, K . L . , and T. L . Swift. 2001. Clutch size relative to tree cavity size in northern flickers. Journal of A v i a n Biology 32: 167-173. Wiebe, K . L . , W . D . Koenig, and K . Martin. 2006. Evolution of clutch size in cavity-excavating birds: the nest site limitation hypothesis revisited. American Naturalist 167: 343-353. 41 C H A P T E R 3: D O E S N E S T - S I T E A V A I L A B I L I T Y L I M I T C A V I T Y - N E S T E R S I N M A T U R E F O R E S T S O F I N T E R I O R B R I T I S H C O L U M B I A ? A N E S T B O X A D D I T I O N E X P E R I M E N T . 2 INTRODUCTION Shelter availability limits populations of shelter-using species in a broad range of systems and taxa. Correlations between shelter availability and population density or survival, as well as experimental manipulations of essential resources, followed by an increase or decline in population or nest density, are often cited as evidence of resource limitation. Twig and stem-nesting ants, shell-using hermit crabs and fish, burrow-using hyrax (Procavia capensis), and salamanders that use small mammal tunnels or runways have all been shown to be limited by the availability of their respective shelters (Vance 1972, Fairall et al. 1986, Kuhlman 1994, Foitzik and Heinze 1998, Faccio 2003, Philpott and Foster 2005, Frederickson 2006). Cavity availability is the primary factor limiting breeding populations of many cavity-nesting birds and mammals (see review in Newton 1994, 1998). Circumstantial evidence that is often cited for nest-site limitation includes a high proportion of occupied cavities (e.g. Edington and Edington 1972, Robb et al. 1996, Bonar 2000, Bai et al. 2003) or a positive correlation between nest or breeding density and cavity or snag density (e.g. Raphael and White 1984, Zarnowitz and Manuwal 1985). Experiments that alter nest-site availability via nest box addition or removal, cavity blocking or creation, or snag removal or creation have provided direct evidence of nest-site limitation in numerous systems. For example, Brawn and Balda (1988) observed an increase in breeding densities of pygmy nuthatches (Sitta pygmaea), western bluebirds (Sialia mexicana) and violet-green swallows (Tachycineta thalassina) after box addition on three treatment sites in 2 A version of this chapter will be submitted for publication. Aitken, K. E. H., and K. Martin. 2007. Does'nest-site availability limit cavity-nesters in mature forests of interior British Columbia? A nest box addition experiment. Journal of Wildlife Management. 42 Arizona. Density of Eurasian kestrels increased after box provisioning in rural farmland habitat in Spain (Fargallo et al. 2001). Population levels of several woodpecker and secondary cavity-nesting species were negatively impacted by removal of snags in pine (Pinus spp.) forests of South Carolina and Arizona, as well as in burned mixed conifer forests in California (Scott 1979, Raphael and White 1984, Lohr et al. 2002). Most studies on cavity-nester population limitation have been conducted in harvested forests, in which natural rates of cavity creation and loss have been altered (Newton 1994, 1998). Most of these studies showed an increase in breeding densities following addition of nest boxes to second-growth forest (e.g. Brawn and Balda 1988, Caine and Marion 1991, Holt and Martin 1997). The few studies conducted in mature or old growth forests suggest that cavity-nesters in undisturbed habitat may be limited by factors other than cavity availability (Gauthier and Smith 1987, Waters et al. 1990, Newton 1994, 1998). In Brawn and Balda's study cited above, nesting densities only increased in treatment sites consisting of young, thinned stands and not in an older forest site. Walankiewicz (1991) found that secondary-cavity nester breeding densities in old growth forests in Poland were limited by predation rather than nest-site availability. In interior British Columbia, Gauthier and Smith (1987) found that territorial behaviour rather than cavity availability limited bufflehead (Bucephala albeola) density. In mature forests with a full complement of excavators and a variety of cavity types, food availability, predation pressure and other social or environmental factors may replace cavity availability as the main drivers of population limitation (Martin and Norris 2007). There is conflicting evidence for the cavity limitation hypothesis in mature mixed conifer forests of interior British Columbia. While cavity densities were low in the region (<2 cavities/ha), cavity occupation rates were also low (< 10%/year; Aitken 2002), suggesting that (he few cavities present may have been of insufficient quality for some secondary users, possibly because they were of unsuitable size, were located in suboptimal habitat, or had other features 43 that made them undesirable. For example, large-bodied cavity-nesters, such as small mammals, ducks, and raptors, rely primarily on cavities created by large excavators, which may be less abundant in the landscape than smaller cavities (Van Balen et al. 1982, Eadie et al. 1998, Martin et al. 2004). Additionally, in an earlier study in the area, I found that stand-scale features such as tree density and proximity to edge influenced nest-site preferences of some cavity-nesters more than cavity or tree characteristics (Aitken 2002, Aitken and Martin 2004). While cavities in general were distributed evenly with respect to edge and interior (Aitken 2002), excavated cavities in coniferous forests were significantly farther from edge than non-excavated cavities (Chapter 2, Figure 2.2), suggesting that cavity quality may vary spatially across the landscape. Thus, cavity quality and location may be more important in limiting cavity-nesting populations than overall cavity abundance (Lohmus and Remm 2005). The objective of my study was to determine whether cavity availability and location limit cavity-nesting populations in mature coniferous forests in interior B C . I conducted a nest box addition experiment in which I increased overall nest-site availability in mature coniferous forest sites with low cavity densities and low occupation rates. Boxes were designed to simulate cavities created by the most common small-bodied and medium-large bodied excavators in the community in order to determine whether low cavity occupancy rates in coniferous forests were due to a lack of excavated cavities with those size characteristics. Additionally, boxes were placed in edge and interior habitat to ascertain whether a low abundance of excavated cavities in edge habitats was limiting cavity-nester populations. I predicted that i f cavities were limiting for • cavity-nesters in coniferous forests, an increase in nest-site availability via box addition would result in an increase in nest density of cavity-nesting species. I predicted that i f availability of large-sized cavities or excavated cavities in edge habitats were limiting for some cavity-nesters, there would be preferential use of large boxes, and boxes in edge habitats. 44 METHODS S t u d y A r e a Research was conducted in seven coniferous forest study sites (Doc English Lake, Maclntyre Lake, Mili tary Gate, Rock Lake, Solitary Woods, Tongue, The Y ; Chapter 1, Figure 1.2) between M a y and July 1996-2006. See Chapter 1 for a detailed description of the study area. Nes t m o n i t o r i n g a n d b o x a d d i t i o n e x p e r i m e n t I utilized a replicated before-after/control-impact (BACI) experimental design (Underwood 1992, 1994), in which I monitored cavities for six years pre-treatment, two years during treatment (box addition), and three years following box removal on three treatment sites (one treatment site, Doc English, was not monitored in 2006) and four control sites. A l l previously active nest trees were marked with numbered aluminum tags and previously active cavities were assigned identifying numbers as part of a larger cavity-nester study operating on the study area since 1995 (Martin and Eadie 1999). From 1 M a y - 31 July, previously active and newly excavated cavities were monitored approximately twice per week. Cavities were checked with a flashlight and mirror and were considered active nests i f they contained at least one egg or nestling. I also recorded cavities used for nesting or roosting by small mammals (Martin et al. 2004). In late July 2001, nest boxes were added to three coniferous forest study sites (Doc English, Maclntyre Lake, and Mili tary Gate; Chapter 1, Figure 1.2). These were sites that had low densities of cavities (1.9 cavities/ha) between 1996-2001, and low nest densities, with cavity occupation rates of <10% per year (Aitken 2002). Boxes were removed in late July 2003, and I continued to monitor nesting in cavities during the 2004-2006 breeding seasons. 45 , Two sizes of nest boxes were used to simulate small and medium-large sized cavities. Thirty-five small-sized boxes were constructed from downed aspen trees, cut into sections approximately 0.5 m long. Sections were hollowed out using a chisel and entrance holes were drilled in each box using a circular saw with a 3.5 cm-diameter blade (9.6 c m 2 entrance area). Pieces of plywood were attached to the tops of boxes,using screws, which could be loosened in order to open the boxes to view the nest contents. Box measurements were: vertical depth x = 17.8 ± 0.72 cm, internal width x = 8.2 ± 0.39 cm, and entrance area x = 12.8 + 0.46 cm 2 . These boxes fell within the range of measurements of cavities created or used by the small-bodied cavity excavators in the study area, such as downy woodpeckers (Picoides pubescens), black-capped chickadees (Poecile atricapillus), and red-breasted nuthatches (Sitta canadensis; Martin et al. 2004). Thirty-five standard rectangular, top-opening plywood boxes were used to simulate cavities created or used by the main larger-bodied cavity excavators in the area, including northern flicker, hairy woodpecker and red-naped sapsucker (Martin et al. 2004). Box measurements were: vertical depth = 23.0 cm, internal width = 23.4 cm, entrance area = 38.5 cm 2 . Five pairs of boxes (1 small, 1 large) were placed in the forest interior (>100m from nearest edge) at each of the three sites, five pairs were placed near grassland edge at two of the sites (<15 m from edge; Doc English, Mili tary Gate), and five pairs were placed near pond edge at two of the sites (<15 m from edge; Doc English, Maclntyre Lake). Boxes within pairs were placed an average of 10m apart and box pairs were spaced an average of 50m apart. Mean height above ground was 3.4 ± 0.1 m for small boxes and 3.3 ± 0.1 m for large boxes. Boxes were nailed to aspen or conifer trees randomly. 46 Data analyses I examined the effect of box addition on total nest density of all cavity-nesting species, and on four species for which sufficient sample sizes were available (mountain chickadee, red-breasted nuthatch, red squirrel, northern flying squirrel). Chickadee nest densities across years on treatment and control sites were examined using linear mixed effects models, and nuthatch and squirrel densities were examined using generalized linear mixed-effects models with a penalized quasi-likelihood method of parameter estimation (glmmPQL). G l m m P Q L is an appropriate statistical analysis when dependent data follow a Poisson distribution, as was the case with my nuthatch and squirrel density data (Breslow and Clayton 1993, Nelson and Leroux 2006). A l l analyses were performed in the statistical package R (R version 2.4.0, R Development Core Team 2006). Treatment type (box addition or control) and period ("pre-treatment": 1996-2001; "during treatment": 2002-2003; and "post-treatment": 2004-2006) were fixed effects, site was a random effect, and square-root transformed nest (or nest and roost) density was the dependent variable. I compared proportions of edge and interior boxes used by mountain chickadees, red squirrels and flying squirrels using Fisher's Exact tests (for chickadees in 2002 and 2003, and for squirrels in 2002), and chi-squared tests (for squirrels in 2003). RESULTS Nest box addition resulted in a 300% increase in nest-site availability on coniferous forest sites, from a mean of 1.2 cavities per hectare before box addition to 3.5 cavities or boxes per hectare with box addition. Cavity-nesting birds and small mammals used 51% of large boxes for nesting or roosting in 2002 and 67% in 2003. Occupancy of small boxes was similar in both years (37% in 2002, 34%> in 2003). The majority of occupied large-sized boxes were used for roosting by small mammals, while small-sized boxes had similar proportions of nests and roosts. In both treatment years, mountain chickadees used boxes in forest interior slightly less than expected 47 from their availability, and used boxes near wet edge more than expected, with both trends being much stronger in 2003 than in 2002 (Figure 3.1a; Fisher's Exact Test, 2002: P = 0.10, 2003: P = 0.008). While nesting and roosting red squirrels and northern flying squirrels preferred boxes near wet edge and avoided boxes in forest interior in 2002, these preferences switched in 2003 (Figure 3.1b; Fisher's Exact Test, 2002: P = 0.02, chi-squared test, 2003: X2 = 3.1, df = 2, P = 0.22). Chewing by squirrels significantly enlarged the entrances of 23 out of 35 small-sized boxes between 2002-2003 (paired samples /-test: / = -4.03, df = 35, P < 0.001), resulting in a mean entrance area of 14.0 cm 2 for small boxes in 2003, compared to a mean of 12.8 c m 2 in 2002. Total density of bird and mammal nests on treatment sites more than tripled in 2002, remained at that level in 2003, and decreased by 35% (from 2003 levels) in 2004 after boxes were removed (Table 3.1, Figure 3.2a). Despite a slight increase in nest density in 2005 due to an increase in woodpecker nests on treatment sites, total nest densities returned to near pre-treatment levels in 2006. The proportion of nests in boxes was 30% of 27 nests in 2002 and 36% of 25 nests in 2003. The increase in total nest density after box addition was largely accounted for by a significant increase in mountain chickadee ( M O C H ) nests on treatment sites (Table 3.1). M O C H nest density increased nearly nine-fold (from 0.04/ha to 0.37/ha) on treatment sites in 2002, remained high in 2003, decreased by 55% in the first year following box removal, and returned to pre-treatment levels in 2006 (Figure 3.2b). The proportion of M O C H nests in boxes increased from 46% of 13 nests in 2002 to 64% of 11 nests in 2003, but this was not significant (X2 = 0.73, df = 1, n = 24, P = 0.39). A l l M O C H nests were in small-sized boxes. Squirrel nest and roost density increased significantly following box addition, and dropped to pre-treatment levels immediately following box removal (Table 3.1, Figure 3.2c). Nearly all squirrel nests and roosts were in boxes (75% of 16 boxes used in 2002 and 85%) of 27 used in 48 2003). Red squirrels preferred large over small boxes in both years (all of 8 boxes used in 2002, and 92% of 13 used in 2003), while flying squirrels preferred small boxes in 2002 (3 of 4 nests/roosts) and large boxes in 2003 (8 of 10 nests/roosts). Interestingly, although only one red-breasted nuthatch pair nested in a box (in 2003), box addition appeared to have a positive effect on nuthatch nest densities on treatment sites (Table 3.1). While sample sizes were low, nuthatch nest density in cavities doubled (from 0.11/ha to 0.2/ha) on treatment sites in 2002, remained high in 2003 and 2004, and returned to pre-treatment levels in 2005 and 2006 (Figure 3.2d). DISCUSSION Numerous studies have examined limitation of cavity-nesting populations by nest-site availability in North America and Europe. Newton (1994) provided a comprehensive review and concluded that while nest-sites may limit populations in harvested forests, other factors may be more important in limiting cavity-nester densities in mature forests where natural processes of cavity creation and decay have not been altered. In the 13 years since his review was published, there have been few nest-site limitation experiments in unharvested or mature forests reported in the literature. Lohr et al. (2002) found a reduction in woodpecker breeding territories in experimental sites in which snags were removed. Common goldeneye (Bucephala clangula) nest density increased following box addition in Finnish forests (Poysa and Poysa 2002), as did densities of mountain chickadees, pygmy nuthatches, and house wrens (Troglodytes aedon) after box addition in Colorado (Bock and Fleck 1995). Many recently published studies have cited circumstantial evidence, such as an abundance of unoccupied holes, to support the contention that cavities may not be limiting in mature forest. To my knowledge, my study is the only recent long-term, replicated nest box addition experiment with before and after treatment data for cavity-nesters in mature mixed conifer forests. 49 The most abundant secondary cavity-nesters on my treatment sites, mountain chickadees, red squirrels and northern flying squirrels, accounted for 37% of cavity nests (n = 131) on the treatment sites over the course of the study, and these three species were the most affected by box addition. While I observed a few nests of mountain bluebirds, tree swallows, and bufflehead (Bucephala alheold) in cavities before and after my box addition experiment, I did not record any nests of these species in boxes or cavities during the treatment period. Bluebirds and swallows are usually associated with aspen groves surrounded by grassland in the study area (Chapter 1), and my coniferous forest sites may not have provided adequate access to foraging habitat for these species (Robertson et al. 1992, Power and Lombardo 1996). Bufflehead appear to prefer cavities excavated by flickers in my study area, and these may be more abundant in aspen groves than in coniferous forest (Aitken et al. 2002, Martin et al. 2004). Additionally, species occurring at low densities may take longer to locate and use boxes added to sites (Brawn andBalda 1988). Response of mountain chickadees to box addition Mountain chickadee density appeared to be influenced by nest-site availability on my study sites, as suggested by a significant increase in nest density following box addition. A s well, M O C H only used small-sized boxes. In a larger study in the area, presented in Chapter 2, nearly all M O C H nests for which hole origin could be determined were in cavities excavated by small to medium-bodied species such as red-breasted nuthatch (34%), red-naped sapsucker (26%), and downy woodpecker (13%). However, the majority of cavities in the study area were excavated by larger-bodied woodpeckers, such as northern flickers, hairy woodpeckers, and pileated woodpeckers (Aitken 2002). As well , M O C H nest cavity volume and entrance size, which may influence reproductive success, predation and competition (Zeleny 1978, Moeed and Dawson 1979, van Balen 1984, Slagsvold 1989, Robertson and Rendell 1990; but see Wiebe 2001) were 50 strongly scaled with chickadee body size (Martin et al. 2004), suggesting that chickadees select nest cavities within an optimal size range. Breeding density of M O C H increased significantly on my treatment sites after the addition of nest boxes within this size range, suggesting that natural cavities with these characteristics may be limited on my study sites. Previous studies found conflicting evidence of nest-site limitation in M O C H , and suggested that the importance of cavity availability in limiting M O C H populations may depend on stand age and food availability (Dahlsten and Copper 1979, Brawn and Balda 1988, Bock and Fleck 1995). In my study area, there was a concurrent outbreak of two preferred chickadee foods, western spruce budworm (Choristoneura occidentalis; Heppner and Turner 2006) and mountain pine beetle (Dendroctonus ponderosae; Martin et al. 2006). The increase in food resources across the study area may have allowed chickadees to respond to the experimental increase in nest-site availability on my treatment sites. Chickadee nest density also increased on control sites, but the smaller magnitude of the increase compared to treatment.sites suggests that other factors such as nest-site availability limited the degree to which chickadees were able to respond to the increase in food availability. If food rather than nest sites primarily limited chickadees, I would have expected a comparable increase in populations across all my study sites, regardless of box addition. This was not the case, leading me to conclude that nest-site availability, rather than food availability, was the main factor limiting M O C H density in my study area. Because I added boxes to treatment sites at the end of July 2001, M O C H had a full winter to assess the increased availability of nest sites prior to the first breeding season of the experiment. Adult M O C H spend the winter in foraging flocks in home ranges encompassing several breeding territories (McCal lum et al. 1999), allowing them to evaluate nest-site availability through the non-breeding season. A s well , local populations include non-breeding "floaters", subordinate adults that acquire territories as more dominant individuals die or shift to 51 higher quality territories (Ho.gstad 1989, Smith 1984, 1989, Mostrom et al. 2002). The increase in nest-site availability via box addition may have provided breeding opportunities for non-breeding floaters in the M O C H population on my treatment sites. It is unlikely that the increase in M O C H nest density was simply due to adults switching from nearby breeding territories to those with boxes as in that case I should have observed a concurrent decline in cavity use within my treatment sites, and no overall increase in nest density. Additionally, many species show an inverse relationship between resource density and territory size (Village 1983, Marshall and Cooper 2004). The increase in nest-site availability on my treatment sites may have resulted in a reduction in territory size among dominant M O C H , allowing floaters to settle in boxes or cavities that might otherwise have been unavailable to them. Response of red squirrels and northern flying squirrels to box addition Red squirrel and northern flying squirrel nest and roost densities increased considerably following box addition on my sites and subsequently crashed when boxes were removed, suggesting that squirrels were limited by nest-site availability. However, previous studies have found that while arboreal squirrels (Tamiasciurus spp. and Glaucomys spp.) readily use nest boxes, this does not always result in an increase in total population size or the proportion of adults breeding (Brady et al. 2000, Carey 2002, Ransome and Sullivan 2004), and that squirrels are primarily limited by food availability (Sullivan 1990, Ransome and Sullivan 1997, 2004). In addition to using cavities, red squirrels and northern flying squirrels construct bolus nests in the tree canopy, and therefore they may not be dependent on cavities as nest and roost sites (Young et al. 2002, Ransome and Sullivan 2004). Because I did not assess squirrel density directly through live trapping and monitoring of breeding adults, I do not know whether total population levels increased following box addition. However, while most cavities in my sites were excavated by larger-bodied woodpecker species, total cavity densities were low (Aitken 2002), 52 and the dramatic increase in squirrel nest and roost density, the preference for large-sized boxes, and enlargement of the entrances of smaller boxes by squirrel chewing, suggests that there may be a shortage of suitable large-sized den sites in the study area. Young et al. (2002) found an inverse relationship between cavity availbility and red squirrel use of alternate den sites, and thus, it is possible that the apparent increase in squirrel densities on my treatment sites was due to a shift from bolus nests to boxes. Further research on squirrel productivity and survival is necessary to determine whether these populations are limited by nest-site availability in mature forests of interior B C . R e s p o n s e o f r ed -b reas ted nu tha tches to b o x a d d i t i o n The increase in red-breasted nuthatch density on treatment sites in my study may have been due to over-winter habitat assessment by nuthatches. Like chickadees, nuthatches are residents that spend the winter in the vicinity of their summer breeding range and can assess, resource availability throughout the year, allowing them to select breeding territories accordingly (Matthysen et al. 1992, Ghalambor and Martin 1999). For example, during the mountain pine beetle outbreak in my study area, nuthatches switched from aspen-dominated nest patches to those containing high densities of beetle-infested pine (Norris 2007). While nuthatches are able to excavate cavities, soft decayed trees may be limited in the landscape (Steeger and Hitchcock 1998, Schepps et al. 1999, Brandeis et al. 2002, Lohr et al. 2002), excavation itself may be energetically costly (Wiebe and Swift 2001), and it can take up to two weeks to complete a cavity (Ghalambor and Martin 1999). Thus, nuthatches often utilize existing holes rather than excavating a new cavity, and approximately 40% of nuthatch nests are in old cavities on my. study sites (Aitken et al. 2002, Wiebe et al. 2006). As well , where nest-site availability is low, interspecific competition for cavities may be intense. Therefore, it is possible that nuthatches assess territory and habitat quality partially on the basis of cavity abundance, which may indicate 53 not just the presence of suitable nest-sites but also the.potential level of interspecific competition for those cavities. Thus, while only one nuthatch pair nested in a box on my treatment sites, the experimental increase in nest-site availability may have enhanced overall habitat quality for nuthatches, leading to an increase in nuthatch breeding densities in cavities in those sites. Conclusions Despite low cavity occupancy rates prior to nest-site supplementation in my study sites at Riske Creek, nest and roost densities increased following box addition. I suggest that the availability of suitable nest and den sites may be limiting for some cavity-nesting populations in these mature coniferous forests, and that cavity size and location may influence the true availability of cavities in the landscape. 54 Table 3.1. M i x e d models predicting density of a) all nests of cavity-nesting birds and mammals, b) mountain chickadee nests, c) red squirrel and northern flying squirrel nests and roosts, and d) red-breasted nuthatch nests in relation to treatment type (box addition or control) and treatment period (pre-treatment, during treatment or post-treatment). Linear mixed effects ( L M E ) models were used to examine chickadee density, while generalized linear mixed-effects models ( G L M M ) were used to examine nuthatch and squirrel densities. L M E and G L M M calculate separate parameter estimates for each level of categorical fixed effects, and report estimates in relation to the first level specified in the data alphabetically. Thus, parameters were calculated in relation to Treatment type = "Box addition" and Period = "During treatment ". For example, the significant negative parameter estimate for total bird and mammal nests in the pre-treatment period indicates that nest density was significantly lower in that period than during treatment. Site was included in the model as a random effect. Parameter Estimate SE df -^statistic P a) Total cavity-nesting birds & mammals Intercept 0.75 0.082 65 9.23 O . 0001 Period: Pre-treatment -0.59 0.068 65 -8.69 O . 0001 Period: Post-treatment -0.25 0.078 65 -3.19 0.002 Treatment type: Control -0.46 0.11 5 . -4.24 0.008 Period: Pre-treatment *Treatment type: Control 0.46 0.090 65 5.09 O . 0001 Period: Post-treatment *Treatment type: Control 0.22 0.10 65 2.15 0.04 b) Mountain chickadee Intercept 0.35 0.040 65 8.73 O . 0001 Period: Pre-treatment -0.32 0.039 65 -8.05 O . 0001 Period: Post-treatment -0.18 0.045 65 -4.01 0.0002 Treatment type: Control -0.19 0.054 5 -3.49 0.02 Period: Pre-treatment *Treatment type: Control 0.19 0.052 65 3.64 0.0005 Period: Post-treatment *Treatment type: Control 0.12 0.059 65 2.05 0.04 Table 3.1, cont'd. _ Parameter Estimate SE df -^statistic P c) Red squirrel and northern flying squirrel Intercept -0.23 0.23 .65 -1.01 0.32 Period: Pre-treatment -4.67 0.79 65 -5.91 O.0001 Period: Post-treatment -2.55 0.43 65 -5.90 O.0001 Treatment type: Control -3.57 0.74 5 -4.81 0.005 Period: Pre-treatment *Treatment type: Control 4.85 1.11 65 4.38 O.0001 Period: Post-treatment *Treatment type: Control 3.48 0.88 65 -3.93 0.0002 d) Red-breasted nuthatch Intercept -1.77 0.28 65 -6.38 O.0001 Period: Pre-treatment -1.15 0.35 65 -3.27 0.002 Period: Post-treatment -0.84 0.41 65 -2.07 0.04 Treatment type: Control -1.11 0.48 5 -2.31 0.07 Period: Pre-treatment *Treatment type: Control 0.46 0.59" 65 0.78 0.44 Period: Post-treatment *Treatment type: Control 0.48 0.66 65 0.73 0.47 as C/3 -(—> o c _o -4—> i— o OH O t-i OH O O t-i . C a <*) +-• C/3 CD a o c _o -I—> o PH O 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 0.6 0.5 0.4 0.3 0.2 0.1 0.0 a) Mountain chickadees 2 2 1 1 b) Red squirrels and northern flying squirrels n r • Used ^ Available Dry edge Wet edge Interior 2002 13 Dry edge Wet edge Interior 2003 Figure 3.1. Proportion of boxes used by a) mountain chickadees, and b) red squirrels and northern flying squirrels compared to proportion of boxes available in dry grassland edge, wet (lake) edge, and forest interior on treatment (box addition) sites in 2002 and 2003. See text for results of Fisher's Exact and chi-square tests. ia) All cavity-nesting birds and mammals O 6 -i b) Mountain chickadee 0.2 H v o t — o o C T \ C 2 — C M c i ^1- »/-> v© 0 1 0 S , 0 - \ 0 - \ C Z 5 C Z > C Z 5 C O C Z 5 C Z 5 C O 0 > O I 0 > CT\ <=>•' C=>. C3> C O C O C O C O ^ - i —^< >—< C N oi y\cs N t s i • y " Pre-treatment 2 1 r r 4 1 r 5 \ : d) Red-breasted nuthatch J During Post-treatment treatment M D t— O O O N O — < C M C«I K~> MD C T \ O S C ^ < 3 1 C O C O C O C O C O C O C O O I O I O I O I C O C O C O C O C O C O C O '—i PI oiy c^s 04 M j v r^ re-treatment During Post-treatment treatment Figure 3.2. Density of cavities or boxes occupied by a) all cavity-nesting bird and mammal species, b) mountain chickadees, c) red squirrels and northern flying squirrels (nests and roosts), and d) red-breasted nuthatches on treatment (boxes added) and control sites. Numbers above error bars are the total active nests on treatment sites, and numbers below bars are the total active nests on control sites. See text for details of statistical analyses. 58 REFERENCES Aitken, K . E . H . 2002. Nest-site availability, selection and reuse in a cavity-nesting community in forests of interior British Columbia. M.Sc . thesis, University of British Columbia, Vancouver, B C . Aitken, K . E . H . , and K . Martin. 2004. Nest cavity availability and selection in aspen-conifer groves in a grassland landscape. Canadian Journal of Forest Research 34: 2099-2109. Aitken, K . E . H . , K . L . Wiebe, and K . Martin. 2002. Nest-site reuse patterns for a cavity-nesting bird community in interior British Columbia. A u k 119: 391-402. Alatalo, R. V . , A . Carlson, and A . Lundberg. 1988. Nest cavity size and clutch size of pied flycatchers Ficedula hypoleuca breeding in natural tree-holes. Ornis Scandinavica 19: 317-319. Bai , M . - L . , F. Wichmann, and M . Muehlenberg. 2003. The abundance of tree holes and their utilization by hole-nesting birds in a primeval boreal forest of Mongolia. Acta Ornithologica 38:95-102. Bock, C. E . , and D . C. Fleck. 1995. Avian response to nest box addition in two forests of the Colorado Front Range. Journal of Field Ornithology 66: 352-362. Bonar, R. L . 2000. Availabil i ty of pileated woodpecker cavities and use by other species. Journal of Wildlife Management 64: 52-59. Brady, M . J., T. S. Risch, and F. S. Dobson. 2000. Availabil i ty of nest sites does not limit population size of southern flying squirrels. Canadian Journal of Zoology 78: 1144-1149. Brandeis, T. J., M . Newton, G . M . Fi l ip , and E . C. Cole. 2002. Cavity-nester habitat development in artificially made Douglas-fir snags. Journal of Wildl i fe Management 66: 625-633. 59 Brawn, J. D . , and R. P. Balda. 1988. Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities? Condor 90: 61-71. Breslow, N . E . , and D . G . Clayton. 1993. Approximate inference in generalized linear mixed models. Journal of the American Statistical Association 88: 9-25. British Columbia Ministry of Forests. 1995. Biodiversity guidebook. B C Ministry of Forests, Victoria, B C . B u l l , E . L . , and J. A . Jackson. 1995. Pileated woodpecker (Dryocopuspileatus). In The Birds of North America, No . .148, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . Caine, L . A . , and W . R. Marion. 1991. Artificial addition of snags and nest boxes to slash pine plantations. Journal of Field Ornithology 62: 97-106. Carey, A . B . 2002. Response of northern flying squirrels to supplementary dens. Wildlife Society Bulletin 30: 547-556. Dahlsten, D . L . , and W . A . Copper. 1979. The use of nesting boxes to study the biology of the mountain chickadee (Parus gambeli) and its impact on selected forest insects. In The role of insectivorous birds in forest ecosystems, J G Dickson, R N Conner, R R Fleet, J C K r o l l , and J A Jackson, Eds. Academic Press, New York, N Y . Daigle, P. 1996. Fire in the dry interior forests of British Columbia. British Columbia Ministry of Forests Extension Note 8. B C Ministry of Forests, Victoria, B C . Dolan, P. G . , and D . C. Carter. 1977. Glaucomys volans. Mammalian Species 78: 1-6. Eadie, J., P. Sherman, and B . Semel. 1998. Conspecific brood parasitism, population dynamics, and the conservation of cavity-nesting birds. In Behavioral ecology and conservation biology, T. Caro, Ed . Oxford University Press, London. Edington, J. M . , and M . A . Edington. 1972. Spatial patterns and habitat partition in the breeding birds of an upland wood. Journal of Animal Ecology 41: 331-357. 60 Faccio, S. D . 2003. Postbreeding emigration and habitat use by Jefferson and Spotted Salamanders in Vermont. Journal of Herpetology 37: 479-489. Fairall, N . , P. J. Vermeulen, and M . Van Per Merwe. 1986. A general model of population growth in the Hyrax, Procavia capensis. Ecological Modell ing 34: 115-132. Fargallo, J. A . , G . Blanco, J. Potti, and J. Vinuela. 2001. Nestbox provisioning in a rural population of Eurasian kestrels: breeding performance, nest predation and parasitism. Bi rd Study 48: 236-244. Foitzik, S., and J. Heinze. 1998. Nest site limitation and colony takeover in the ant Leptothorax nylanderi. Behavioral Ecology 9: 367-375. Frederickson, M . E . 2006. The reproductive phenology of an Amazonian ant species reflects the seasonal availability of its nest sites. Oecologia 149: 418-427. Gauthier, G . , and J. N . M . Smith. 1987. Territorial behaviour, nest site availability, and breeding density in Buffleheads. Journal of Animal Ecology 56: 171-184. Ghalambor, C. K . , and T. E . Martin. 1999. Red-breasted nuthatch (Sitta canadensis), No . 459. In The Birds of North America, A . Poole and F. G i l l , Eds. The Birds of North America Inc., Philadelphia, P A . Heppner, D . , and J, Turner. 2006. Spruce weevil and western spruce budworm forest health stand establishment decision aids. B C Journal of Ecosystems and Management 7: 45-49. Hogstad, O. 1989. Social organization and dominance behaviour in some Parus species. Wilson Bulletin 101: 254-262. Holt, R. F., and K . Martin. 1997. Landscape modification and patch selection: the demography of two secondary cavity nesters colonizing clearcuts. Auk 114: 443-455. Jackson, J. A . , H . R. Ouellet, and B . J. S. Jackson. 2002. Hairy woodpecker (Picoides villosus). In The Birds of North America, No. 702, A . Poole and F. G i l l , Eds. The Birds of North America Inc., Philadelphia, P A . 61 Kuhlman, M . L . 1994. Indirect effects of a predatory gastropod in a seagrass community. Journal of Experimental Marine Biology and Ecology 1 8 3 : 163-178. Leonard, D . L . , Jr. 2001. Three-toed woodpecker (Picoides tridactylus). In The Birds of North America, No. 588, A . Poole and F. G i l l , Eds. The Birds of North America Inc., Philadelphia, P A . Lohmus, A . , and J. Remm. 2005. Nest quality limits the number of hole-nesting passerines in their natural cavity-rich habitat. Acta Oecologica 27: 125-128. Lohr, S. M . , S. A . Gauthreaux, and J. C. Ki lgo . 2002. Importance of coarse woody debris to avian communities in loblolly pine forests. Conservation Biology 1 6 : 767-777. Marshall, M . R., and R. J. Cooper. 2004. Territory size of a migratory songbird in response to caterpillar density and foliage structure. Ecology 8 5 : 432-445. Martin, K . , and J. M . Eadie. 1999. Nest webs: a community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management 1 1 5 : 243-257. Martin, K . , K . E . H . Aitken, and K . L . Wiebe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. Condor 1 0 6 : 5-19. Martin, K . , A . R. Norris, and M . Drever. 2006. Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: implications for critical habitat management. B C Journal of Ecosystems and Management 7: 10-24. Martin, K . , and A . R. Norris. 2007. Life in the small-bodied cavity-nester guild: demography of sympatric mountain and black-capped chickadees within nest web communities under changing habitat conditions. Chapter 8 in The ecology and behaviour of chickadees and titmice: an integrated approach, K Otter, Ed. Oxford University Press, Oxford. 62 Martin, T. E . 1993. Evolutionary determinants of clutch size in cavity-nesting birds: nest predation or limited breeding opportunities? American Naturalist 142: 937-946. Matthysen, E . , D . Cimprich, and T. C. Grubb Jr. 1992. Is social organization in winter determined by short or long-term benefits? A case study on migrant red-breasted nuthatches Sitta canadensis. Ornis Scandinavica 23: 43-48. McCal lum, D . A . , R. Grundel, and D . L . Dahlsten. 1999. Mountain chickadee (Poecile gambeli), No . 453. In The Birds of North America, A . Poole and F. G i l l , Eds. The Birds of North America Inc., Philadelphia, P A . McClel land, B . R., and P. T. McClel land. 2000. Red-naped sapsucker nest trees in northern Rocky Mountain old-growth forest. Wilson Bulletin 112: 44-50. Meidinger, D. , and J. Pojar. 1991. Ecosystems of British Columbia, B C . Ministry of Forests Special Report Series 6, Victoria, B C . Moeed, A . , and D . . G . Dawson. 1979. Breeding of starlings Sturnus vulgaris in nest boxes of various types. New Zealand Journal of Zoology 6: 613-618. Mostrom, A . M . , R. L . Curry, and B . Lohr. 2002. Carolina Chickadee (Poecile carolinensus), No. 636. In The Birds of North America, A . Poole and F. G i l l , Eds. The Birds of North America Inc., Philadelphia, P A . Nelson, K . P., and B . G . Leroux. 2006. Statistical models for autocorrelated count data. Statistics in Medicine 25: 1413-1430. Newton, I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biological Conservation 7 0 : 265-276. Newton, I. 1998. Population limitation in birds. Academic Press, San Diego, C A . Norris, A . R. 2007. The effects of resource variability and community dynamics on chickadee and nuthatch populations. M.Sc . thesis, University of British Columbia, Vancouver, B C . 63 Philpott, S. M . , and P. F. Foster. 2005. Nest-site limitation in coffee agroecosystems: artificial nests maintain diversity of arboreal ants. Ecological Applications 15: 1478-1485. Power, H . W. , and M . P. Lombardo. 1996. Mountain bluebird (Sialia currucoides). In The Birds of North America, No. 222, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . Poysa, H . , and S. Poysa. 2002. Nest-site limitation and density dependence of reproductive output in the common goldeneye Bucephala clangula: implications for the management of cavity-nesting birds. Journal of Applied Ecology 39: 502-510. R Development Core Team. 2006 R: A language and environment for statistical computing. R Foundation for Statistical Computing. Vienna, Austria. Ransome, D . B . , and T. P. Sullivan. 1997. Food limitation and habitat preference of Glaucomys sabrinus and Tamiasciurus hudsonicus. Journal of Mammalogy 78: 538-549. Ransome, D . B . , and T. P. Sullivan. 2004. Effects of food and den-site supplementation on populations of Glaucomys sabrinus and Tamiasciurus douglasii. Journal of Mammalogy 85: 206-215. Raphael, M . G. , and M . White. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada (California, U S A ) . Wildlife Monographs, No. 86. The Wildlife Society, Bethesda, M D . Robb, J. R., M . S. Cramer, A . R. Parker, and R. P. Urbanek. 1996. Use of tree cavities by fox squirrels and raccoons in Indiana. Journal of Mammalogy 77: 1017-1027. Robertson, R. J., and W . B . Rendell. 1990. A comparison of the breeding ecology of a secondary cavity nesting bird, the tree swallow (Tachycineta bicolor), in nest boxes and natural cavities. Canadian Journal of Zoology 68: 1046-1052. Robertson, R. J., B . J. Stutchbury, and R. R. Cohen. 1992. Tree swallow (Tachycineta bicolor), No. 11. In The Birds of North America, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . 64 Schepps, J., S. Lohr, and T. E . Martin. 1999. Does tree hardness influence nest-tree selection by primary cavity nesters? A u k 116: 658-665. Scott, V . E . 1979. Bi rd response to snag removal in ponderosa pine. Journal of Forestry 76: 26-28. • Slagsvold, T. 1989. On the evolution of clutch size and nest size in passerine birds. Oecologia 79: 300-305. Smith, S. M . 1984. Flock switching in chickadees Parus atricapillus: why be a winter floater? American Naturalist 123: 81-98. Smith, S. M . 1989. Black-capped chickadee summer floaters. Wilson Bulletin 101: 344-349. Smith, S. M . 1993. Black-capped chickadee (Poecile atricapillus). In The Birds of North America, No. 39, A . Poole, P. Stettenheim, and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . Steeger, C , and C. L . Hitchcock. 1998. Influence of forest structure and diseases on nest-site selection by red-breasted nuthatches. Journal of Wildlife Management 62: 1349-1358. Sullivan, T. P. 1990. Responses of Red Squirrel Tamiasciurus hudsonicus populations to supplemental food. Journal of Mammalogy 71: 579-590. Underwood, A . J. 1992. Beyond B A C I : the detection of environmental impacts on populations in the real, but variable, world. Journal of Experimental Marine Biology and Ecology 161: 145-178. Underwood, A . J. 1994. On beyond B A C I : sampling designs that might reliably detect environmentaldisturbances. Ecological Applications 4: 3-15. VanBalen , J H . 1984. The relationship between nest-box size, occupation and breeding parameters, of the great tit Parus major and some other hole-nesting species. Ardea 71: 163-175. 65 Vance, R. R. 1972. Competition and mechanism of coexistence in three sympatric species of intertidai hermit crabs. Ecology 53: 1062-1074. Village, A . 1983. The role of nest site availability and territorial behaviour in limiting the breeding density of kestrels Falco tinnunculus. Journal of An ima l Ecology 52: 635-646. Walankiewicz, W . 1991. Do secondary cavity-nesting birds suffer more from competition for cavities or from predation in a primeval deciduous forest? Natural Areas Journal 11: 203-212. Waters, J. R., B . R. Noon, and J. Verner. 1990. Lack of nest site limitation in a cavity-nesting bird community. Journal of Wildlife Management 54: 239-245. Wesolowski, T. 2002. Antipredator adaptations in nesting marsh tits Parus palustris - the role of nest site security. Ibis 144:593-601 Wiebe, K . L . 2001. Clutch size relative to tree cavity size in Northern Flickers: Journal of Avian Biology 32: 167-173. Wiebe, K . L . , and T. L . Swift. 2001. Clutch size relative to tree cavity size in northern flickers. Journal of Avian Biology 32: 167-173. Wiebe, K . L . , W . D . Koenig, and K . Martin. 2006. Evolution of clutch size in cavity-excavating birds: the nest site limitation hypothesis revisited. American Naturalist 167: 343-353. Young, P. J., V . L . Greer, and S. K . Six. 2002. Characteristics of bolus nests of red squirrels in the PinalenO and White Mountains of Arizona. Southwestern Naturalist 47: 267-275. Zarnowitz, J. E . , and D . A . Manuwal. 1985. The effects of forest management on cavity-nesting birds in northwestern Washington, U S A . Journal of Wildlife Management 49: 255-263. Zeleny, L . 1978. Nesting box programs for bluebirds and other passerines. In Endangered birds: management techniques for preserving threatened species, S A Temple, Ed. University of Wisconsin Press. 66 C H A P T E R 4: R E S P O N S E O F S E C O N D A R Y C A V I T Y - N E S T E R S T O A N E X P E R I M E N T A L R E D U C T I O N I N C A V I T Y A V A I L A B I L I T Y : R E S O U R C E S E L E C T I O N P L A S T I C I T Y A N D S P E C I E S I N T E R A C T I O N S . 3 I N T R O D U C T I O N Cavity-nesting communities, which are structured hierarchically based on production of and competition for suitable cavities, are comprised of species that range in their degree of nest-site specialization and dominance (Martin and Eadie 1999). Nesting resources may be limited or unpredictable for these species (Newton 1994) and individuals that are able to exploit a range of nest sites may have greater opportunities for breeding than individuals that are restricted in their nest-site requirements. Secondary cavity-nesting species, which cannot excavate their own cavities, rely on cavities created by woodpeckers or on a limited number of naturally occurring non-excavated cavities, and while landscape-level cavity abundance may be relatively stable, there may be considerable local variation in cavity availability and quality (Aitken and Martin 2004, Aitken and Martin, in review). Thus, cavity-nesting communities provide an opportunity to study the effects of changes in resource availability on species across a range of resource acquisition strategies. Resource selection plasticity and behavioural dominance may influence a species' ability to respond to temporal and spatial changes in resource availability, particularly i f dominant species have highly specialized resource requirements. Subordinate species with more generalized resource preferences than dominant species-may be better able to withstand stochasticity in resource availability (Pimm and Pimm 1982, Palmer 2003). Additionally, plasticity in nest-site selection may allow individuals to utilize a broader range of habitat types, and to reduce nest 3 A version of this chapter has been submitted for publication. Aitken, K . E. H . , and K. Martin. 2007. Plasticity in resource selection affects community responses to an experimental reduction in availability of a critical resource. Ecology. (In review, June 2007). 67 predation and interspecific competition (Albano 1992, Cuervo 2004, Forstmeier and Weiss 2004, Eggers et al. 2006). Thus, the extent to which natural and human-induced environmental variability impact community structure and stability may be influenced by the ecological plasticity of component species (Brown et al. 2001, Hooper et al. 2005, Richmond et al. 2005). Cavity density in mature aspen (Populus tremuloides) groves in the Cariboo-Chilcotin region of British Columbia, Canada, averages 16/ha with overall occupancy rates of 35-44% (Aitken 2002, Aitken and Martin 2004). However, occupancy rates of individual cavities vary, as some cavities are occupied every year while others are occupied only sporadically (Aitken et al. 2002). Among "high occupancy" cavities (those occupied annually or biannually), cavity nesters exhibited preferences related to cavity age, size and proximity to edge (Aitken et al. 2002, Aitken and Martin 2004). Thus, while nest sites may appear to be abundant, individual species' preferences may influence true nest-site availability. Using a cavity blocking experiment, I altered the availability of high occupancy cavities in order to: a) examine changes in nesting abundance at the cavity-nester community- and species-levels in response to changes in the availability of an essential resource, tree cavities, and b) determine whether secondary cavity-nesters in a natural landscape with an apparent abundance of cavities were, in fact, nest-site limited. I predicted that i f nest-site availability were limited for some species in this community, nest abundance of these species would be correlated with changes in cavity abundance. M E T H O D S Study area ' Research was conducted between 2000-2005 in 20 aspen groves (0.1-1.7 ha each), each spaced 16-222 m from the nearest grove or forest and dominated by trembling aspen, with varying amounts of lodgepole pine and Douglas-fir. See Chapter 1 for a complete study area description. 68 Nest monitoring and cavity blocking experiment I utilized a replicated before-after/control-impact (BACI) experimental design (Underwood 1992, 1994), in which I monitored cavities for two years prior to treatment (cavity blocking), two years during treatment, and two years following cavity reopening in seven treatment aspen groves and 13 control groves. A l l previously active nest trees were marked with numbered aluminum tags and previously active cavities were assigned identifying numbers as part of a larger cavity-nester study operating on the study area since 1995 (Martin and Eadie 1999). From 1 M a y - 31 July, previously active and newly excavated cavities were monitored approximately twice per week. Cavities were checked with a flashlight and mirror and were considered active nests i f they contained at least one egg or nestling. I also recorded cavities used for nesting by small mammals (Martin et al. 2004). In Apr i l 2002, prior to the start of the breeding season, I blocked all high occupancy cavities (those that had been occupied in the previous two years; Aitken et al. 2002) on treatment sites using plastic garden mesh stapled over the cavity entrance. I blocked 36 of 80 cavities on treatment sites (45%), representing 30-80% of cavities in each aspen grove. However, five blocked cavities were repeatedly chewed open by small mammals and, thus, were considered as unblocked in subsequent analyses. Overall, cavity blocking resulted in a 47% decrease in cavity abundance, from a pre-treatment mean of 27.9 cavities/ha to 14.8 cavities/ha during treatment. I removed the blocking material in late July 2003, and continued to follow nesting on all 20 sites during the 2004 and 2005 breeding seasons. Data analyses I examined the effect of cavity blocking on nest abundance of all cavity-nesting birds and mammals, and three secondary cavity-nester species for which sufficient data were available (> 69 10 nests per year): European starling, mountain bluebird and tree swallow. I used generalized linear mixed-effects models using a penalized quasi-likelihood method of parameter estimation in the statistical package R (glmmPQL; R version 2.4.0, R Development Core Team 2006). G l m m P Q L is an appropriate statistical analysis when dependent data follow a Poisson distribution, as was the case with my nest abundance data (Breslow and Clayton 1993, Nelson and Leroux 2006). Treatment type (cavity blocking or control) and period ("pre-treatment": 2000-2001; "during treatment": 2002-2003; and "post-treatment": 2004-2005) were fixed effects, site was a random effect, and nest abundance was the dependent variable. R E S U L T S Cavity blocking resulted in a significant decline in overall abundance of cavity nesters (Table 4.1). Total abundance of bird and mammal nests on treatment sites decreased by 41% in 2002 and a further 13% in 2003, resulting in a total decrease in nest abundance of 49% over the two treatment years (Figure 4.1a). Total nest abundance returned-to near pre-treatment levels in 2004 (Figure 4.1a). The decline in total nest abundance after cavity blocking was largely accounted for by a significant decline in European starling (the most abundant secondary cavity-nester) nests on treatment sites (Table 4.1). Starling nests decreased by 72% on treatment sites in.the first year after blocking (2002) and a further 60% in 2003, resulting in a total decrease of 89% in abundance in the two years cavities were blocked (Figure 4. lb). There was a corresponding increase in starling nest abundance on control sites in the second treatment year (2003). After blocking materials were removed from cavities, starling nest abundance did not return to pre-treatment levels, and remained lower on treatment sites than on controls in both 2004 and 2005. Cavity blocking had a significant positive effect on mountain bluebird nest abundance, with an increase in nest numbers beginning in the second year of cavity blocking and continuing 70 until the end of the study (Table 4.1, Figure 4.1c). Tree, swallow nest abundance was not significantly affected by cavity blocking, although there was a slight increase in abundance on control sites in 2004 after cavities were reopened (Figure 4.Id). D I S C U S S I O N At the community level, cavity-nesting bird and mammal populations decreased following cavity blocking and returned to pre-treatment levels following cavity reopening, suggesting that the cavity-nesting community as a whole was limited by cavity abundance. However, species-level resistance to fluctuations in resource availability appeared to play a role in driving the community-level response. Species with generalist nest cavity preferences, such as bluebirds and swallows, displayed high resistance in nest abundance following the experimental decrease in cavity availability, while the most dominant, specialist cavity-nester, European starling, displayed low resistance and resilience to cavity blocking. Generalist species may be better able to withstand stochasticity in resource availability than specialists (Pimm and P imm 1982, Palmer 2003), while specialists may put more effort into acquiring a limited number of higher quality resources. Response of European starlings to cavity blocking Abundance of starlings declined significantly immediately after cavity blocking and did not recover after cavities were reopened. Interestingly, all seven starling nests in my treatment sites in 2002 and 2003 were in the only remaining cavities with characteristics similar to cavities previously occupied by starlings on those sites (K. E . H . Aitken and K . Martin, unpublished data). Thus, it appears that starlings selected all the preferred remaining cavities and, once those were occupied, remaining breeders moved to other aspen groves rather than occupying less suitable cavities within treatment sites. A slight increase in starling nest abundance on nearby 71 control sites in the second treatment year may support this hypothesis. Although starlings are considered nest-site generalists because they have adapted successfully to nesting in both natural and human-made structures, nest-site selection studies suggest that they have specialized nest-site preferences. In Poland, starlings had stronger preferences for nesting cavities based on tree species, height above ground, and cavity entrance shape than did most other species in the community (Wesolowski 1989). Starlings in the Netherlands and Sweden preferred cavities that were large internally (van Balen et al. 1982, Carlson et al. 1998). Earlier, I found that starlings preferred nest-sites that were larger internally, closer to grassland edge, and in trees with only one cavity (Aitken and Martin 2004). Starlings in urban areas of Ontario used a smaller range of human-made structures for nesting and with a narrower range in characteristics than did another introduced secondary cavity-nester, the house sparrow (Passer domesticus; Savard and Falls 1981). Lohmus and Remm (2005) suggested that availability of high quality nest-sites, as opposed to total cavity abundance, may limit some populations of secondary cavity-nesters. M y results suggest that starling populations may be limited by the availability of suitable cavities with a relatively narrow range of preferred characteristics. Studies have noted a delayed response of some secondary cavity-nesters to changes in nest site availability (Brawn and Balda 1988), particularly among species that prospect for nest-sites for use in subsequent years (Eadie and Gaulthier 1985, Stutchbury and Robertson 1987, Holt and Martin 1997, Poysa and Poysa 2002). Non-breeding starlings (floaters) prospect for cavities for the following year by examining cavities occupied by conspecifics, particularly during the nestling period (Tobler and Smith 2004). This may explain the sustained negative impact of cavity blocking on starling nest abundance. Floaters that prospected for cavities on my treatment sites in 2001 (prior to cavity blocking) may have overestimated cavity availability for the following year, while birds prospecting in 2003 may have underestimated cavity availability for 2004. Additionally, because starlings are semi-colonial and may use conspecific breeding 72 activity as an indicator of nest-site suitability (Tobler and Smith 2004), the low densities of breeders on the treatment sites in 2002 and 2003 may have dissuaded other starlings from returning to those sites in subsequent years, regardless of cavity availability in 2004 and 2005. Response of mountain bluebirds and tree swallows to cavity blocking Overall, mountain bluebird and tree swallow nest abundances were not affected negatively by the experimental reduction in cavity availability in this study. Both species are secondary cavity-nesters that co-occur with a range of other cavity-nesting species in a variety of habitats throughout North America and display generalist nest-site preferences (Robertson et al. 1992, Power and Lombardo 1996). I found that in addition to tree cavities, bluebirds and tree swallows used cavities in downed trees, crevices behind bark, hollow stumps, cracks in boulders, and even metal bridge pieces for nesting (Martin et al. 2004, Aitken and Martin, in review). Plasticity, in nest-site selection may have enabled bluebirds and tree swallows to respond quickly to the experimental changes in cavity availability in my study. Role of interspecific dominance in species' responses to cavity blocking Cavity blocking resulted in an increase in mountain bluebird nest abundance in the second year of the experiment and continued for at least two years after cavities were reopened. This increase appeared to correspond with the decrease in starling abundance, suggesting that bluebird populations may be limited by starling presence, either through aggressive interactions or through exploitation competition (Ingold 1994,.Sara et al. 2005). I suspect the latter because starlings initiate nesting approximately 1-2 weeks earlier on average than do bluebirds (K. Martin, unpublished data) and I have never observed direct aggression between the two species on my sites. Previous studies showed that the presence of starlings may influence nest-site selection and timing of breeding by some native cavity-nesters (Kerpez and Smith 1990, Pell and 73 Tidemann 1997, Ingold 1998, Fisher and Wiebe 2006). For example, Davis et al. (1986) found that starlings exclude bluebirds from potential nest sites through their earlier timing of breeding or that bluebirds initiate nesting later to avoid competition with starlings. When nesting in areas with starlings, eastern bluebirds (Sialia sialis) nested in cavities with smaller entrances than in areas without starlings (Pinkowski 1976). Mountain bluebirds shifted to smaller and deeper cavities after starlings became established in central British Columbia in the 1960s (Peterson and Gauthier 1985). Plasticity in nest-site selection and nesting phenology may allow bluebirds to coexist with and avoid direct competition with starlings. Starlings are considered to be' aggressive competitors in North America, Australia and other regions where they have been introduced, with potentially detrimental effects on populations of native cavity-nesters (Kerpez and Smith 1990, Cabe 1993, Pell and Tidemann 1997). However, starlings may not be as adaptable and resilient as they are generally considered given recent declines in starling populations in Europe, possibly due to changes in agriculture and loss of foraging habitat (Rintala et al. 2003, Svensson 2004, Laiolo 2005, Robinson et al. 2005). A review of North American Breeding Bi rd Survey and Christmas Bi rd Count trends found no evidence that starlings have severely impacted populations of cavity-nesters since their introduction (Koenig 2003). P imm and Pimm (1982) suggested that behaviourally dominant species are more likely to be affected by disturbance than are subordinates, i f the dominant species is restricted to higher quality resources while the subordinates are capable of using poorer resources. M y results suggest that inflexibility in starling nest-site preferences, and plasticity in nest-site preferences and nesting phenology of native cavity-nesting species, may enable coexistence of starlings with native species. 74 Experiments on population limitation in cavity-nesters To my knowledge, the cavity blocking experiment presented here is the first involving a replicated before-after/control-impact (BACI) design with multiple treatment and control sites, several years of data, and involving multiple species. Most studies of population limitation in cavity-nesters involve addition or removal of nest boxes, and very few studies have experimentally reduced or increased the availability of natural cavities. In one of the few studies involving artificial cavity excavation, Walters et al. (1992) found an increase in breeding territory abundance of red-cockaded woodpeckers (Picoides borealis) after drilling cavities in live pine (Pinus spp.) trees in North Carolina. A few studies found that removal of all snags in experimental plots resulted in a reduction in cavity-nester breeding densities but these studies did not address cavity availability directly (Scott 1979, Raphael and White 1984, Lohr et al. 2002). The few studies that involved cavity blocking experiments lacked long-term data or adequate replication (e.g. Brush 1983, Waters et al. 1990). Breeding biology and nest predation risk may differ between birds nesting in boxes versus natural cavities (Nilsson 1984, Robertson and Rendell 1990, Kuitunen and Aleknonis 1992, Purcell et al. 1997, Wesolowski and Stanska 2001, Evans 2002). Thus, cavity blocking experiments may provide a more accurate reflection of population responses to variation in resource availability. While experiments that alter the availability of natural cavities may be logistically more difficult than nest box experiments, these methods deserve consideration by researchers examining population limitation in cavity-nester communities. Conclusions Ecological plasticity may allow species to withstand or even benefit from environmental stochasticity and to cope with interspecific competition (Ostfeld and Keesing 2000, Moreno et al. 2001, Yang 2004). However, plastic or generalist species may face trade-offs between using 75 abundant but low quality resources versus rare high quality resources (Abrams 1990). For secondary cavity-nesters. such as bluebirds and tree swallows, selecting an abundant but low-quality cavity may reduce competition and energy spent on searching for a nest-site, but may also result in lower reproductive success i f that cavity is more vulnerable to predation, is not close to optimal foraging habitat, or has poor thermal qualities (Slagsvold 1986, Sedgeley 2001, Lohmus 2003, Lohmus and Remm 2005). Conversely, secondary cavity-nesters that select a more rare but higher quality cavity may suffer reproductive costs i f they expend more energy in locating or defending that nest-site than in egg-laying, incubation or parental care (Duckworth 2006). Cavity-nesters with less plastic nest-site preferences or in habitats with a dearth of cavities may simply defer breeding i f suitable high quality nest-sites are not available (Holt and Martin 1997). Further studies on trade-offs in resource availability and quality for cavity-nesters, and resource partitioning by cavity-nesters, w i l l allow for a better understanding of the mechanisms of species coexistence in these communities. 76 Table 4.1. Generalized linear mixed models ( G L M M ) predicting nest abundance of a) all birds and mammals, b) European starling, c) mountain bluebird, and d) tree swallow in relation to treatment type (cavity blocking or control) and period (pre-blocking, during blocking or post-blocking). G L M M calculates parameter estimates for each level of categorical fixed effects, and reports estimates in relation to the first level specified in the data alphabetically. Thus, parameters reported here were calculated in relation to Treatment type = "Blocking" and Period = "During blocking ". Thus, the significant positive parameter estimate for total bird and mammal nests in the pre-blocking period indicates that nest abundance was significantly higher in that period than during treatment. Site was included in the model as a random effect. a) Total birds and mammals b) European starling Parameter Estimate SE df t P Estimate SE df t P Intercept 1.06 0.20 96 5.18 O.0001 -1.30 0.54 96 -2.42 0.02 Treatment type: control 0.47 0.25 18 1.89 0.07 1.37 0.63 18 2.17 0.04 Period: Pre-blocking 0.57 0.15 96 3.72 0.0003 1.52 0.35 96 4.40 <0.0001 Period: Post-blocking 0.50 0.15 , 96 3.24 0.002 -0.15 0.46 96 -0.33 0.7 Period: preblocking * -0.57 0.18 96 -3.12 0.002 -1.31 0.39 96 -3.36 0.001 Treatment type: control Period: post-blocking * -0.55 0.18 96 -2.97 0.004 -0.05 0.50 96 -0.10 0.9 Treatment type: control c) Mountain bluebird d) Tree swallow Parameter Estimate SE df t P Estimate SE df t P Intercept -0.62 0.36 96 -1.73 0.09 -0.66 0.45 96 -1.45 0.2 Treatment type: control 0.17 0.43 18 0.39 0.7 0.23 0.55 18 0.42 0.7 Period: Pre-blocking -0.29 0.39 96 -0.73 0.5 0.00 0.35 96 0.00 1.0 Period: Post-blocking 0.69 0.32 96 2.20 0.03 0.20 0.34 96 0.59 0.6 Period: preblocking * 0.34 0.45 96 0.74 0.5 -0.08 0.41 96 -0.19 0.8 Treatment type: control Period: post-blocking * -0.80 0.39 96 -2.02 0.046 -0.09 0.39 96 -0.23 0.8 Treatment type: control 8.0 " 6 . 0 1 % 5.0 3 4.0 on CU | 2:0 1.0 0.0 a) A l l nests b) European starling Treatment o- •• Control "i ; r 1 r c) Mountain bluebird d) Tree swallow 2000 2001 2002 2003 2004 2005 S v , K v ' S > ' Pre- During Post-blocking blocking blocking 2000 2001 2002 2003 2004 2005 V V ' V r — J " y ' Pre- During Post-blocking blocking blocking Figure 4.1. Mean nest abundance of a) all cavity-nesting birds and mammals, b) European starlings, c) mountain bluebirds, and d) tree swallows on 7 treatment (cavity blocking) and 13 control sites at Riske Creek, BC. Sample sizes shown beside points are the total sample of nests. 78 REFERENCES Abrams, P. A . 1990. Adaptive responses of generalist herbivores to competition: convergence or divergence. Evolutionary Ecology 4: 103-114. Aitken, K . E . H . 2002. Nest-site availability, selection and reuse in a cavity-nesting community in forests of interior British Columbia. M.Sc . thesis, University of British Columbia, Vancouver, B C . Aitken, K . E . H.'and K . Martin. 2004. Nest cavity availability and selection in aspen-conifer groves in a grassland landscape. Canadian Journal of Forest Research 34: 2099-2109. Aitken, K . E . H . , K . L Wiebe, and K . Martin. 2002. Nest-site reuse patterns for a cavity-nesting bird community in interior British Columbia. A u k 119: 391-402. Albano, D . J. 1992. Nesting mortality of Carolina chickadees breeding in natural cavities. Condor 94: 371-382. Brawn, J. D . , and R. P. Balda. 1988. Population biology of cavity nesters in northern Arizona: do nest sites limit breeding densities? Condor 90: 61-71. Breslow, N . E . , and D . G Clayton. 1993. Approximate inference in generalized linear mixed models. Journal of the American Statistical Association 88: 9-25. Brown, J. H . , T. G . Whitman, S. K . Morgan Ernest, and C. A . Gehring. 2001. Complex species interactions and the dynamics of ecological systems: long-term experiments. Science 293: 643-650. Brush, T. 1983. Cavity use by secondary cavity-nesting birds and response to manipulations. Condor 85:. 461-466. Cabe, P. R. 1993. European Starling (Sturnus vulgaris). In The Birds of North America, no. 48, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . 79 Carlson, A . , U . Sandstrom, and K . Olsson. 1998. Availabili ty and use of natural tree holes by cavity nesting birds in a Swedish deciduous forest. Ardea 8 6 : 109-119. Cuervo, J. J. 2004. Nest-site selection and characteristics in a mixed-species colony of Avocets Recurvirostra avosetta and Black-winged stilts Himantopus himantopus. B i rd Study 5 1 : 20-24. Davis, W . H . , W . C. McComb, and P. N . Allaire. 1986. Nest box use by starlings: does it inhibit bluebird production? Transactions of the Kentucky Academy of Science 4 7 : 133-136. Duckworth, R. A : 2006. Behavioral correlations across breeding contexts provide a mechanism for a cost of aggression. Behavioral Ecology 1 7 : 1011-1019. Eadie, J. M . , and G . Gauthier. 1985. Prospecting for nest sites by cavity-nesting ducks of the genus Bucephala. Condor 8 7 : 528-534. Eggers, S., M . Griesser, M . Nystrand, and J. Ekman. 2006. Predation risk induces changes in nest-site selection and clutch size in the Siberian jay. Proceedings of the Royal Society B -Biological Sciences 2 7 3 : 701-706. Evans, M . R. 2002. A comparison of the characteristics and fate of Barrow's goldeneye and bufflehead nests in nest boxes and natural cavities. Condor 1 0 4 : 610-619. Fisher, R., and K . Wiebe. 2006. Nest site attributed and temporal patterns of northern flicker nest loss: effects of predation and competition. Oecologia 1 4 7 : 744-753. Forstmeier, W. , and I. Weiss. 2004. Adaptive plasticity in nest-site selection in response to changing predation risk. Oikos 1 0 4 : 487-499.. . Holt, R. F., and K . Martin. 1997. Landscape modification and patch selection: The demography of two secondary cavity-nesters colonizing clearcuts. A u k 1 1 4 : 443-455. Hooper, D . U . , E.S Chapin m, J. J Ewel , A . Hector, P. Inchausti, S. Lavorel, J. H . Lawton, D . M . Lodge, M . Loreau, S. Naeem, B . Schmid, H . Setala, A . J. Symstad, J. Vandermeer, and D. A . 8.0 Wardle. 2005. Effects of biodiversity on ecosystem functioning: a consensus of current knowledge. Ecological Monographs 75: 3-35. Ingold, D . J. 1994. Influence of nest-site competition between European starlings and woodpeckers. Wilson Bulletin 106: 227-241. Ingold, D . J. 1998. The influence of starlings on flicker reproduction when both naturally excavated cavities and artificial nest boxes are available. Wilson Bulletin 110: 218-225. Kerpez, T. A . , and N . S. Smith. 1990. Competition between European Starlings and native woodpeckers for nest cavities in saguaros. Auk 107: 367-375. Koenig, W . D . 2003. European starlings and their effect on native cavity-nesting birds. Conservation Biology 17: 1134-1140. Kuitunen, M . , and A . Aleknonis. 1992. Nest predation and breeding success in Common Treecreepers nesting in boxes and natural cavities. Ornis Fennica 69: 7-12. Laiolo, P. 2005. Spatial and seasonal patterns of bird communities in Italian agroecosystems. Conservation Biology 19: 1547-1556. Lohmus, A . 2003. Do Ural owls (Strix uralensis) suffer from the lack of nest sites in managed forests? Biological Conservation 110: 1-9. Lohmus, A . , and J. Remm. 2005. Nest quality limits the number of hole-nesting passerines in their natural cavity-rich habitat. Acta Oecologica.27: 125-128. Lohr, S. M . , S. A . Gauthreaux, and J. C. Ki lgo . 2002. Importance of coarse woody debris to avian communities in loblolly pine forests. Conservation Biology 16: 767-777. Martin, K . , K . E . H . Aitken, and K . L . Wiebe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. Condor 106: 5-19. 81 Martin, K . , and J. M . Eadie. 1999. Nest webs: a community-wide approach to the management and conservation of cavity-nesting forest birds. Forest Ecology and Management 115: 243-257. Moreno, E . , M . Barluenga, and A . Barbosa. 2001. Ecological plasticity by morphological design reduces costs of subordination: influence on species distribution. Oecologia 128: 603-607. Nelson, K . P., and B . G . Leroux. 2006. Statistical models for autocorrelated count data. Statistics in Medicine 25: 1413-1430. Newton, I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biological Conservation 70: 265-276. Nilsson, S. G . 1984. Clutch size and breeding success of the Pied Flycatcher Ficedula hypoleuca in natural tree-holes. Ibis 126: 407-410. Ostfeld, R. S., and F. Keesing. 2000. Pulsed resources and community dynamics of consumers in terrestrial ecosystems. Trends in Ecology and Evolution 15: 232-237. Palmer, T. M . 2003. Spatial habitat heterogeneity influences competition and coexistence in an African acacia ant guild. Ecology 84: 2843-2855. Pell , A . S., and C. R. Tidemann. 1997. The impact of two exotic hollow-nesting birds on two native parrots in savannah and woodland in eastern Australia. Biological Conservation 79: 145-153. Peterson, B . , and G . Gauthier. 1985. Nest site use by cavity-nesting birds of the Cariboo Parkland, British Columbia. Wilson Bulletin 97: 319-331. Pimm, S. L . , and J. W . Pimm. 1982. Resource use, competition, and resource availability in Hawaiian honeycreepers. Ecology 63: 1468-1480. Pinkowski, B . C. 1976. Use of tree cavities by nesting Eastern Bluebirds. Journal of Wildlife Management 40: 556-563. 82 Power, H . W. , and M . P. LombardO. 1996. Mountain Bluebird (Sialia currucoides). In The Birds of North America, No . 222, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . Poysa, H . , and S. Poysa. 2002. Nest-site limitation and density dependence of reproductive output in the common goldeneye Bucephala clangula: implications for the management of cavity-nesting birds. Journal of Applied Ecology 3 9 : 502-510. Purcell, K . L . , J. Verner, and L W . Oring. 1997. A comparison of the breeding ecology of birds nesting in boxes and tree cavities. Auk 114: 646-656. R Development Core Team. 2006. R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. Raphael, M . G. , and M . White. 1984. Use of snags by cavity-nesting birds in the Sierra Nevada (California, U S A ) . Wildlife Monographs 86: 1-66. Richmond, C. E . , D : L . Breitburg, and K . A . Rose. 2005. The role of environmental generalist species in ecosystem function. Ecological Modell ing 188: 279-295. Rintala, J., J. Tiainen, and T. Pakkala. 2003. Population trends of the Finnish starling Sturnus vulgaris, 1952-1998, as inferred from annual ringing totals. Annales Zoologici Fennici 40: 365-385. Robertson, R. J., and W . B . Rendell. 1990. A comparison of the breeding ecology of a secondary cavity nesting bird, the tree swallow (Tachycineta bicolor), in nest boxes and natural cavities. Canadian Journal of Zoology 68: 1046-1052. Robertson, R. J., B . J. Stutchbury, and R. R. Cohen. 1992. Tree Swallow (Tachycineta bicolor). In The Birds of North America, No. 11, A . Poole, P. Stettenheim, and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . 83 Robinson, R. A . , G . M . Siriwardena, and H . Q. P. Crick. 2005. Status and population trends of starling, Sturnus vulgaris, in Great Britain. B i rd Study 52: 252-260. Sara, M . , A . Milazzo, W . Falletta, and E . Bell ia. 2005. Exploitation competition between hole-nesters (Muscicardinus avellanarius, Mammalia and Parus caeruleus, Aves) in Mediterranean woodlands. Journal of Zoology 265: 347-357. Savard, J -R L . , and J. B . Falls. 1981. Influence of habitat structure on the nesting height of birds in urban areas. Canadian Journal of Zoology 59: 924-932. Scott, V . E . 1979. B i rd response to snag removal in ponderosa pine. Journal of Forestry 76: 26-28. Sedgeley, J. A . 2001. Quality of cavity microclimate as a factor influencing selection of maternity roosts by a tree-dwelling bat, Chalinolobus tuberculatus, in New Zealand. Journal of Applied Ecology 38: 425-438. Slagsvold, T. 1986. Nest site settlement by the pied flycatcher Ficedula hypoleuca: does the female choose her mate for the quality of his house or himself? Ornis Scandinavica 17: 210-220. " Stutchbury, B . J., and R. J. Robertson. 1987. Behavioral tactics of subadult female floaters in the tree swallow. Behavioral Ecology and Sociobiology 20: 413-419. Svensson, S. 2004. The recent decline of the Starling Sturnus vulgaris population in Sweden: a 22-year nest-box study. Ornis Svecica 14: 28-46. Tobler, M . , and H . G . Smith. 2004. Specific floater home ranges and prospective behaviour in the European starling, Sturnus vulgaris. Naturwissenschaften 91: 85-89. Underwood, A . J. 1992. Beyond B A C I : the detection of environmental impacts on populations in the real, but variable, world. Journal of Experimental Marine Biology and Ecology 161: 145-178. 84 Underwood, A . J. 1994. On Beyond B A C I : sampling designs that might reliably detect environmental disturbances. Ecological Applications 4: 3-15. Van Balen, J. H . , C . J. H . Booy, J. A . van Franeker, and E . R. Osieck. 1982. Studies on hole-nesting birds in natural nest sites: 1. Availabili ty and occupation of natural nest sites. Ardea 70: 1-24. Walters, J. R., C. K . Copeyon, and J. H . Carter III. 1992. Test of the ecological basis of cooperative breeding in Red-cockaded woodpeckers. A u k 109: 90-97. Waters, J. R., B . R. Noon, and J. Verner. 1990. Lack of nests site limitation in a cavity-nesting bird community. Journal of Wildlife Management 54: 239-245. Wesolowski, T. 1989. Nest-sites of hole nesters in a primaeval temperate forest, Bialowieza National Park, Poland. Acta Ornithologica 25:321-351. Wesolowski, T., and M . Stanska. 2001. High ectoparasite loads in hole-nesting birds - a nestbox bias? Journal of Avian Biology 32: 281-285. Yang, L . H . 2004. Periodical cicadas as resource pulses in North American forests. Science 306: 1565-1567. 85 C H A P T E R 5: G E N E R A L D I S C U S S I O N A N D C O N C L U S I O N S T H E S I S S U M M A R Y Nest cavities created by woodpeckers or natural decay processes are an essential commodity for secondary cavity-nesting species. In harvested forests, some populations of cavity-nesters may be limited by the availability of suitable cavities (Newton 1994). Additionally, woodpeckers are often considered keystone species in forest systems because they can influence the diversity and abundance of other cavity-nesters in the community (Daily et al. 1993, Mikuskinski and Angelstam 1997, Martin and Eadie 1999, Aubry and Raley 2002, Duncan 2003). However, little is understood about the relative importance of excavated versus non-excavated holes for cavity-nesters, and the role of nest-site availability in limiting populations across different forest types and conditions (Martin and Wesolowski, in review). It has been suggested that in mature forests, with a full complement of excavators and undisrupted processes of cavity creation and loss, factors other than cavity availability may limit populations of cavity-nesters (Waters et al. 1990, Walankiewicz 1991, Newton 1994, Martin et al. 2004). M y study showed that, while cavities created by woodpeckers and other excavators were considerably more abundant in coniferous forests and aspen groves of Becher's Prairie, B C , most secondary cavity-nesters used them at random relative to their availability (Chapter 2). In mature coniferous forests, mountain chickadee nest density appeared to be limited by cavity availability, and there appeared to be a shortage of large-sized den sites for red squirrels and northern flying squirrels (Chapter 3). Cavity availability appeared to limit the abundance of nesting European starlings in mature aspen groves, while starling abundance appeared to limit mountain bluebird nest abundance (Chapter 4). M y results suggest that the sizeable and diverse assemblage of excavators on Becher's Prairie may contribute to the high abundance of cavities in the area, but that these cavities vary in suitability and quality for secondary cavity-nesters. 86 Additionally, for some species such as bluebirds, cavity availability may be limited indirectly, via exploitative competition from other species. Thus, cavity-nester populations may be influenced by the abundance and distribution of cavities, but responses are modulated by cavity-nester community dynamics. Further research into intra- and interspecific partitioning of nest-sites, and the influence of competition and predation from small mammals using cavities, wi l l help to elucidate mechanisms of species coexistence in these complex communities. Below, I highlight some knowledge gaps in cavity-nesting community ecology and suggest directions for future research. K N O W L E D G E G A P S A N D S U G G E S T I O N S F O R F U T U R E R E S E A R C H Intra- and interspecific partitioning of cavities The influence of cavity creation rates and longevity on niche partitioning in cavity-nesting communities is poorly understood. While resource abundance, predictability and seasonality can affect resource partitioning and competition (Tilman 1982, Gil ler 1984), few studies of community structure examine relationships with resource availability and suitability (Giller 1984, Pulliam 2000). The predictability of a resource may influence the ability of species to specialize on that resource, and high predictability favours smaller niche breadths (Cody 1974). Conversely, high resource seasonality of turnover favours broader niches. Individual nest cavities may persist in the landscape for several years and may be reused multiple times by various occupants both within and across years (Aitken et al. 2002). However, disease and stage of tree decay influence excavation activities by woodpeckers and weak excavators (Harestad and Keisker 1989, Schepps et al. 1999), which in turn influences the types of holes excavated and the rate of hole creation (McLaren 1962, Conner et al. 2001). Additionally, as cavities age, they may decay, become filled with nest material, be enlarged by woodpeckers or squirrels (Conner et al. 2001, Chapter 3), or be destroyed during nest predation attempts (DeWeese and Pillmore 87 1972, Aitken, personal obs.). Long-term cavity monitoring studies are needed in order to determine the influence of cavity creation, longevity, and loss on cavity-nesting community structure and dynamics. Resource availability and limitation are primary factors influencing niche partitioning (Hutchinson 1957, Pulliam 2000). Many studies have examined the influence of interspecific competition on resource selection and niche partitioning in a variety of species, including desert ants (Aphaenogaster spp.), geese (Anser spp.), warblers (Vermivora spp.) and tits (Parus spp.; Herrera 1978, Madsen 1985, Sanders and Gordon 2000, Martin and Martin 2001). However, most of these studies focused on closely related species, which presumably overlap considerably in most aspects of their life history, such as foraging and nesting niches. Shelter-using communities, in contrast, provide an opportunity to study resource use and niche partitioning among diverse groups of species or taxa, which may only overlap in one portion of their total niche, reducing the relative amount of overlap in total niche space among the species in the community. Because tree holes are essential for reproduction in cavity-nesters and, therefore, are likely to be a primary resource for which species compete, cavity-nesting communities provide an excellent system in which to examine resource partitioning across taxa and trophic levels. Few studies have directly examined nest-site partitioning in cavity-nesting communities. Peterson and Gauthier (1985) compared nest cavity characteristics of several species in interior British Columbia seven years and 25 years after European starlings reached the area. They found that mountain bluebirds shifted to deeper nest cavities, while northern flickers shifted to narrower cavities. Several researchers have suggested that some cavity nesters use small diameter cavities to avoid competition with European starlings for larger holes (Peterson and Gauthier 1985, Rendell and Robertson 1989). For example, Dobkin et al. (1995) found that tree swallows nesting in preferred starling habitat close to woodland edge only used small red-naped 88 sapsucker cavities. Swallows nesting >15 m from edge shifted to northern flicker cavities. Similarly, Pinkowski (1976) found that eastern bluebirds nesting in areas with starlings used cavities with smaller entrances than in areas without starlings. However, most of these studies were short-term or hampered by small sample sizes, and none examined the impact of niche shifts on reproductive success of cavity nesters. . Long-term, large-scale community-level studies of nest-site selection in relation to changes in cavity availability and population densities of potential competitors are necessary to understand resource partitioning in cavity-nesting communities. Specifically, there is a need for studies examining how species with overlapping nest-site requirements partition cavities temporally and spatially, and how morphological and life history factors of cavity-nesting species influence niche breadth, overlap and flexibility. Niche partitioning and flexibility may be examined by comparing relative resource use among populations of species under varying habitat, temporal and competitive conditions (Llewellyn and Jenkins 1987, Ki ldaw 1999). Influence of competition and predation by small mammals on cavity availability and selection Few studies have examined the influence of small mammals on nest-site availability and selection in cavity-nesting communities. In Europe, several species of dormouse (Family Gliridae) are nest-site competitors and predators of cavity-nesting birds (Juskaitis 2006), and have been shown to influence nest-site availability and selection for other species in the community (Sara et al. 2005). On Becher's Prairie, red squirrels, northern flying squirrels, bushy-tailed woodrats, weasels (Erminea spp.), marten and fisher (Martes spp.), and deer mice use cavities for nesting, roosting, food storage and other activities. Because these species are resident throughout the year, they may influence availability and quality of nest-sites in several ways. In Chapter 3,1 showed that chewing of box entrances resulted in a significant increase in 89 entrance size, and most boxes and cavities used by squirrels were filled with nest material such as grass, moss and lichen, possibly reducing cavity useability for other species. Cavities may also be filled with winter food caches, rendering them unuseable for other cavity-nesters in the spring i f the stores have not been depleted. This impact may be particularly significant for migratory birds that arrive in spring after small mammals, which begin breeding as early as March, have occupied preferred cavities, especially for medium to large-bodied birds that use cavities in the same size range as squirrels. Finally, in addition to competing with other cavity-nesters for nest-sites, most of these small mammal species prey on cavity-nesting adults, eggs or nestlings (Robertson et al. 1992, Power and Lombardo 1996, Bradley and Marzluff 2003). This interesting dynamic is largely unexplored in these communities as small mammals tend to be under-sampled or not monitored in many cavity-nester studies, and their role in cavity-nesting community ecology requires further examination. Predation risk can influence nest-site selection (Martin and Roper 1988, Hogstad 1995, Eggers et al. 2006), and a better understanding of the predator assemblage is needed for the cavity-nesting community of Becher's Prairie. Currently, only anecdotal evidence exists regarding which species prey on adults, juveniles, nestlings or eggs of cavity-nesters in this .region. Black bears (Ursus americanus) prey on nests of flickers and cavity-nesting ducks in the Cariboo-Chilcotin (Walters and Mi l le r 2001, Evans et al. 2002, K . L . Wiebe, unpublished data). Identification of hairs left at the entrances of some depredated nests suggests that red squirrels, flying squirrels and marten (Martes americana) prey on eggs, nestlings and possibly adults in cavities (Evans et al. 2002, Mahon and Martin 2004, K . E . H . Aitken and K . Martin, unpublished data). Other potential nest predators recorded in the area include weasels (Mustela spp.), marten and fisher {Martes spp.), chipmunks (Eutamius spp.), American Crows (Corvus brachyrhynchos), and carpenter ants (Camponotus spp; Ki lham 1971, Keisker 1987, Power and Lombardo 1996, Martin et al. 2006). Several woodpeckers, including northern flickers and 90 pileated woodpeckers, prey on eggs and nestlings of cavity-nesters (Loftin and Leeds 1981, Robertson et al. 1992, Christman and Dhondt 1997). Understanding predation pressures w i l l help explain nest-site selection patterns in cavity-nesting communities, and shed light on whether a high abundance of unused cavities in the landscape indicates that nest-sites are not limiting for cavity-nesters, or whether an excess of unoccupied holes is a strategy by cavity-nesters to reduce predation risk by increasing search times of predators (Watts 1987, Martin and Roper 1988). Summary The role of nest-site availability in limiting cavity-nesting populations in mature forests, and the importance of woodpeckers as cavity providers, may depend on the abundance and quality of non-excavated holes, as well as the cavity and habitat attributes associated with the woodpecker species present. On my study sites in interior British Columbia, woodpeckers created the majority of cavities in the landscape but these were not selected preferentially by secondary cavity-nesters and instead were used in proportion to their abundance. Thus, while woodpeckers may play a role in providing a copious supply of cavities in this system, many of the secondary cavity-nesters in the community are not solely reliant on excavated holes for nesting. Additionally, while nest-sites may initially appear to be abundant and potentially non-limiting at the community level, individual species preferences, as well as interspecific interactions, may influence true nest-site availability. REFERENCES Aitken, R . E . H . , K . L . Wiebe, and K . Martin. 2002. Nest site reuse patterns for a cavity-nesting bird community in interior British Columbia. Auk 1 1 9 : 391-402. Bradley, J. E . and J. M . Marzluff. 2003. Rodents as nest predators: influences on predatory behaviour and consequences to nesting birds. Auk 1 2 0 : 1180-1187. 91 Christman, B . J., and A . A . Dhondt. 1997. Nest predation in Black-capped Chickadees: how safe are cavity nests? A u k 114: 769-773. Cody, M . L . 1974. Competition and the structure of bird communities. Princeton University Press, Princeton, N J . Conner, R. N . , D . C. Rudolph, and J. R. Walters. 2001. The Red-cockaded Woodpecker: surviving in a fire-maintained ecosystem. University of Austin Press, Austin, T X . DeWeese, L . R., and R. E . Pillmore. 1972. Bi rd nests in an aspen tree robbed by black bear. Condor 74: 488. Dobkin, D. S., A . C. Rich, J. A . Pretare, and W . H . Pyle. 1995. Nest-site relationships among cavity-nesting birds of riparian and snowpocket aspen woodlands in the northwestern Great Basin. Condor 97: 694-707. Dolan, P. G . , and D . C. Carter. 1977. Glaucomys volans. Mammalian Species 78: 1-6. Eggers, S., M . Griesser, M . Nystrand, and J. Ekman. 2006. Predation risk induces changes in nest-site selection and clutch size in the Siberian jay. Proceedings of the Royal Society B -Biological Sciences 273: 701-706. Evans, M . R., D . Lank, W . S. Boyd, and F. Cooke. 2002. A comparison of the characteristics and fate of Barrow's Goldeneye and Bufflehead nests in nest boxes and natural cavities. Condor 104: 610-619. Giller, P. S. 1984. Community structure and the niche. Chapman and Hal l , London. Harestad, A . S., and D. G . Keisker. 1989. Nest tree use by primary cavity-nesting birds in south central British Columbia. Canadian Journal of Zoology 67: 1067-1073. Herrera, C. M . 1978. Niche shift in the genus Parus in southern Spain. Ibis 120: 236-240. Hogstad, O. 1995. Do avian and mammalian nest predators select for different nest dispersion patterns of Fieldfares Tardus pilaris?: a 15-year study. Ibis 137: 484-489. 92 Hutchinson, G . E . 1957. Concluding remarks. Cold Spring Harbor Symposium on Quantitative Biology 22: 415-427. Jactel, H . , M ! Goulard, P. Menassieu, and G . Goujon. 2002. Habitat diversity in forest plantations reduces infestations of the pine stem borer Dioryctria sylvestrella. Journal of Applied Ecology 39: 618-628. Juskaitis, R. 2006. Interactions between dormice (Gliridae) and hole-nesting birds in nestboxes. Folia Zoologica 55: 225-236. Keisker, D . G . 1987. Nest tree selection by primary cavity-nesting birds in south-central British Columbia. Wildlife Report No. R-13, Wildlife Branch, B C Ministry of Environment and Parks, Victoria, B C . Ki ldaw, S. D . 1999. Competitive displacement? A n experimental assessment of nest site preferences of cliff-nesting gulls. Ecology 80: 576-586. Ki lham, L . 1971. Reproductive behavior of yellow-bellied sapsuckers, part 1: preference for nesting in Fomes-mfected aspens and nest hole interrelations with flying squirrels, raccoons and other animals. Wilson Bulletin 83: 159-171. Kuitunen, M . , and A . Aleknonis. 1992. Nest predation and breeding success in Common Treecreepers nesting in boxes and natural cavities. Ornis Fennica 69: 7-12. Llewellyn, J. B , and S. H . Jenkins. 1987. Patterns of niche shift in mice: Seasonal changes in microhabitat breadth and overlap. American Naturalist 129: 365-381. Loftin, R. W. , and J. Leeds. 1981. Pileated woodpecker Dryocopus pileatus takes red-bellied woodpecker Melanerpes carolinus nestling. Florida Field Naturalist 9: 41. Madsen, J. 1985. Habitat selection of farmland feeding geese in West Jutland, Denmark: A n example of a niche shift. Ornis Scandinavica 16: 140-144. Mahon, C. L . , and K . Martin. 2004. Nest survival of chickadees in managed forests: habitat, predator and year effects. Journal of Wildlife Management 70: 1257-1265. Martin, K . , A . R. Norris, and M . Drever. 2006. Effects of bark beetle outbreaks on avian biodiversity in the British Columbia interior: implications for critical habitat management. B C Journal of Ecosystems and Management 7: 10-24. Martin, P. R., and T. E . Martin. 2001. Ecological and fitness consequences of species coexistence: A removal experiment with wood warblers. Ecology 82: 189-206. Martin, T. E . , and J. J. Roper. 1988. Nest predation and nest-site selection of a western population of the Hermit Thrush. Condor 90: 51-57. McLaren, W . D. 1962. A preliminary study of nest-site competition in a group of hole-nesting birds. M S c thesis: University of British Columbia, Vancouver, B C . Newton, I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biological Conservation 70: 265-276. Nilsson, S. G . 1984. Clutch size and breeding success of the Pied Flycatcher Ficedula hypoleuca in natural tree-holes. Ibis 126: 407-410. Peltonen, M . 1999. Windthrows and dead-standing trees as bark beetle breeding material at forest-clearcut edge. Scandinavian Journal of Forest Research 14: 505-511. Peterson, B . , and G . Gauthier. 1985. Nest site use by cavity-nesting birds of the Cariboo Parkland, British Columbia. Wilson Bulletin 97: 319-331. Pinkowski, B . C. 1976. Use of tree cavities by nesting Eastern Bluebirds. Journal of Wildlife Management 40: 556-563. Power, H . W. , and M . P. Lombardo. 1996. Mountain bluebird (Sialia currucoides), No . 222. In The Birds of North America, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . Pulliam, H . R. 2000. On the relationship between niche and distribution. Ecology Letters 3: 349-361. 94 Purcell, K . L . , J. Verner, and L . W . Oring. 1997. A comparison of the breeding ecology of birds nesting in boxes and tree cavities. Auk 114: 646-656. Rendell, W . B . , and R. J. Robertson. 1989. Nest-site characteristics, reproductive success and cavity availability for Tree Swallows breeding in natural cavities. Condor 91: 875-885. Robertson, R. J., and W . B . Rendell. 1990. A comparison of the breeding ecology of a secondary cavity nesting bird, the tree swallow (Tachycineta bicolor), in nest boxes and natural cavities. Canadian Journal of Zoology 68: 1046-1052. Robertson, R. J., B . J. Stutchbury, and R. R. Cohen. 1992. Tree swallow (Tachycineta bicolor), No. II. In The Birds of North America, A . Poole and F. G i l l , Eds. The Academy of Natural Sciences, Philadelphia, P A ; The American Ornithologists' Union, Washington, D C . Sanders, N . J., and D . M . Gordon. 2000. The effects of interspecific interactions on resource use and behavior in a desert ant. Oecologia 125: 436-443. Sara, M . , A . Milazzo, W . Falletta, and E . Bell ia. 2005. Exploitation competition between hole-nesters (Muscardinus avellanarius, Mammalia and Parus caeruleus, Aves) in Mediterranean woodlands. Journal of Zoology 265: 347-357. Schepps, J., S. Lohr, and T. E . Martin. 1999. Does tree hardness influence nest-tree selection by primary cavity nesters? Auk 116: 658-665. Tilman, D . 1982. Resource competition and community structure. Princeton University Press, Princeton, N J . Walankiewicz, W . 1991. Do secondary cavity-nesting birds suffer more from competition for cavities or from predation in a primeval deciduous forest? Natural Areas Journal 11: 203-212. Walters, E . L . , and E . H . Mil ler . 2001. Predation on nesting woodpeckers in British Columbia. Canadian Field-Naturalist 115:413-419. 95 Waters, J. R., B . R. Noon, and J. Verner. 1990. Lack of nest site limitation in a cavity-nesting bird community. Journal of Wildlife Management 54: 239-245. Wattsm B . D . 1987. Old nest accumulation as a possible protection mechanism against search-strategy predators. Animal Behaviour 35: 1566-1568. Wesolowski, T., and M . Stanska. 2001. High ectoparasite loads i i i hole-nesting birds - a nestbox bias? Journal of Avian Biology 32: 281-285. 96 

Cite

Citation Scheme:

        

Citations by CSL (citeproc-js)

Usage Statistics

Share

Embed

Customize your widget with the following options, then copy and paste the code below into the HTML of your page to embed this item in your website.
                        
                            <div id="ubcOpenCollectionsWidgetDisplay">
                            <script id="ubcOpenCollectionsWidget"
                            src="{[{embed.src}]}"
                            data-item="{[{embed.item}]}"
                            data-collection="{[{embed.collection}]}"
                            data-metadata="{[{embed.showMetadata}]}"
                            data-width="{[{embed.width}]}"
                            async >
                            </script>
                            </div>
                        
                    
IIIF logo Our image viewer uses the IIIF 2.0 standard. To load this item in other compatible viewers, use this url:
http://iiif.library.ubc.ca/presentation/dsp.831.1-0074957/manifest

Comment

Related Items