UBC Theses and Dissertations

UBC Theses Logo

UBC Theses and Dissertations

Breeding bird communities and habitat associations in the grasslands of the Chilcotin Region, British… Hooper, Tracey D 1994

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

Item Metadata

Download

Media
831-ubc_1994-0522.pdf [ 1.83MB ]
Metadata
JSON: 831-1.0087683.json
JSON-LD: 831-1.0087683-ld.json
RDF/XML (Pretty): 831-1.0087683-rdf.xml
RDF/JSON: 831-1.0087683-rdf.json
Turtle: 831-1.0087683-turtle.txt
N-Triples: 831-1.0087683-rdf-ntriples.txt
Original Record: 831-1.0087683-source.json
Full Text
831-1.0087683-fulltext.txt
Citation
831-1.0087683.ris

Full Text

BREEDING BIRD COMMUNITIES and HABITAT ASSOCIATIONS in the GRASSLANDS of the CHILCOTIN REGION, BRITISH COLUMBIA  by  TRACEY DENINE HOOPER B.Sc., The University of Victoria,  1985  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE  in  THE FACULTY OF GRADUATE STUDIES (Department of Plant Science)  We accept this thesis as conforming to the required standard  Signature(s) removed to protect privacy  THE UNIVERSITY OF BRITISH COLUMBIA October 1994 ©  Tracey Define Hooper,  1994  In presenting this thesis in  partial fulfilment of the requirements for an advanced  degree at the University of British Columbia, I agree that the Library shall make it freely available for reference and study. I further agree that permission for extensive copying of this thesis for scholarly purposes may be granted by the head of my department  or  by  his  or  her  representatives.  It  is  understood  that  copying  or  publication of this thesis for financial gain shall not be allowed without my written permission.  Signature(s) removed to protect privacy  (Signature)  Department of  ‘v-  The University of British Columbia Vancouver, Canada  Date  DE-6 (2/88)  1E3,  ;11L]  abstract The objectives of this study were (1) to characterize breeding bird communities in the grasslands around Riske Creek, in the Chilcotin Region of British Columbia,  (2) to identify  associations between grassland habitat characteristics and breeding bird diversity and species abundances,  (3) to determine  the relationship between food resource availability and grassland bird diversity and species abundances, and (4) to elucidate the potential impacts of livestock grazing on breeding birds and their grassland habitats. Point—counts and spot—mapping methods were used to census birds.  Habitat characteristics measured were vegetation height,  vertical cover, and patchiness, horizontal cover of different physiognomic features, arthropod abundances, and site slope, aspect, elevation.  The season, intensity, and grazing by  livestock and California bighorn sheep within th study area were also determined.  Principal component, multiple correlation, and  cluster analyses were used to analyze bird/habitat associations. Eleven species of birds were common throughout the study area.  They were, in order of decreasing abundance: horned lark  (Eremophila alestris), vesper sparrow (Pooecetes gramineus), European starling (Sturnus vulgaris), western meadowlark (Sturnella neglecta), long—billed curlew (Numenius americanus), Brewer’s blackbird (Euihagus cyanocephalus), tree swallow (Tachycineta bicolor), mountain bluebird (Sialia currucoides), American crow (Corvus brachyrhynchos), savannah sparrow i_i  (Passerculus sandwichensis), and red crossbill (Loxia Three red—listed (i.e., threatened or endangered)  curvirostra).  species (upland sandpiper (Bartramia lonciicauda), Sprague’s pipit (Anthus spragueii), Brewer’s sparrow (Spizella breweri)) and two blue-listed (vulnerable) species (sharp-tailed grouse (Tympanuchus phasianellus) and short—eared owl (Asio flammeus)), were also recorded.  Over 13 study sites, bird density ranged  from 0.82 to 1.24 pairs/ha and Shannon’s species diversity indices ranged from 0.71 to 1.38. Vegetation structure and patchiness, horizontal cover, topographic features, and grazing characteristics combined, explained 15-96% of the variability in bird diversity and species abundances.  Topographic features were most often associated with  bird diversity and species abundances, possibly due to correlations between topography and vegetation structure. Vegetation structural components were the second most common features associated with birds. Although arthropod abundances explained 15—72% of variability in bird diversity and species abundances, associations between birds and food resources were often unclear.  Associations between birds and grazing were also  unclear.  111  Table of Contents  . A1 stract . . . Tableof Contents ListofTables Listof Figures. Acknowledgements  1.  2  .  .  .  •  .  .  .  .  .  •  .  .  .  .  .  .  . .  .  .  .  •  .  •  .  .  .  .  .  .  .  .  •  .  .  .  .  .  .  .  .  .  .  •  .  .  .  .  .  .  .  .  • . Introduction . . . . • 1.1 Literature Review . . . . . . . 1.1.1 Grassland Bird Communities and Habitats . . . . . . 1.1.2 Influences of Livestock Grazing on Grassland Bird Communities and Habitats . • . 1.2 Objectives . . . 1.3 Research Hypotheses  Study Area  .  .  .  .  :1_i  iv vii ix x .  .  1 3 3 5 8 8 10  . . • 3. Methods . 3.lStudySites. . . . . . . . . 3.2 Grassland Breeding Bird Censuses 3.2.1 Species Censuses . 3.2.2 Long—billed Curlew Censuses 3.3 Habitat Characteristics . 3.3.1 Vegetation Structure . • . Height and Vertical Cover . Horizontal Cover . . . . Vegetation Patchiness . • 3.3.2 Vegetation Species Composition 3.3.3 Food Resources 3.3.4 Grazing Information . . . . . . . . 3.3.5 Topographic Features . 3.4 Habitat Structure Use by Birds 3.5 Statistical Analyses . . . . . .  14 14 14 14 17 17 17 17 18 19 19 20 21 22 23 24  4 Results . 4.1 Bird Censuses . . . . . 4.2 Long-billed Curlew Breeding Densities 4.3 Bird/habitat Associations . . 4.3.1 Principal Component Analysis 4.3.2 General Bird/habitat Correlations 4.3.3 Specific Bird/habitat Correlations Species Diversity . . . . . • • HornedLark. • • . • Vesper Sparrow . . . . Long—billed Curlew Western Meadowlark . . . . . . iv  27 27 29 32 32 34 39 39 39 39 40 40  • . • Brewer’s Blackbird Tree Swallow • • . • . • Mountain Bluebird • • • Savannah Sparrow Upland Sandpiper • . • Sprague’sPipit Brewer’s Sparrow • • . . • Sharp—tailed Grouse . • • • • • Short—earedOwl. . . . • 4.3.4 Species Management Guidelines • Species Diversity . HornedLark. • • • • • • • • • • • VesperSparrow • • . • Long—billedCurlew Western Meadowlark • • • • . • • • • • • UplandSandpiper Sprague’sPipit. . . . • • 4.3.5 Habitat Management Guidelines . 4.3.6 Habitat Structure Use by Birds  . 5 Discussion . 5.1 Bird Censuses . . . . . . . . 5.2 Long—billed Curlew Censuses . 5.3 General Bird/habitat Associations 5.4 Specific Bird/habitat Associations 5.4.1 Species diversity . 5.4.2 Horned Lark 5.4.3 Vesper Sparrow . . 5.4.4 Long-billed Curlew 5.4.5 Western Meadowlark 5.4.6 Brewer’s Blackbird 5.4.7 Tree Swallow . . . . 5.4.8 Mountain Bluebird . . 5.4.9 Savannah Sparrow . . 5.4.10 Upland Sandpiper . . 5.4.11 Sprague’s Pipit . . Brewer’s 5.4.12 Sparrow . . 5.4.13’Sharp—tailed Grouse 5.4.14 Short—eared Owl . . 5.5 Habitat Structure Use by Birds  6 Conclusions  .  .  .  .  .  .  .  .  7 Management Recommendations 8 Literature Cited 9Appendices  •  •  .  .  .  .  .  .  .  .  •  .  •  •  •  •  .  •  • •  . •  .  •  •  •  •  •  •  •  •  •  41 41 41 42 42 42 43 43 43 43 43 44 44 50 52 54 54 54 55  •  .  •  .  •  •  •  •  •  •  .  •  •  •  •  •  .  .  •  .  •  .  •  •  58 58  •  .  .  .  •  .  66  .  75  . •  •  .  .  •  •  •  .  .  .  •  .  • •  •  • •  •  .  76 78 78 79 80 80 81  •  •  83  .  .  .  .  .  .  •  •  87  .  •  .  •  .  •  .  .  99  10 Appendix 1: Bird species censused in the Chilcotin study area, British Colubia, 1991/92 11 Appendix 2: Codes for habitat variables v  .  •  99 102  12 Appendix 3: Plant species recorded in the Chilcotin study area, British Columbia, 1992  .  13 Appendix 4: Chi-square analysis of habitat structural use among horned larks, vesper sparrows, western meadowlarks, and mountain bluebirds in the Chilcotin study area, British Columbia, 1991/92 . . . .  .  .  103  105  14 Appendix 5: Chi-square analysis of habitat structural use by horned larks, vesper sparrows, western meadowlarks, and mountain bluebirds in the Chilcotin study area, British Columbia, 1991/92  .  .  .  .  .  .  .  .  .  .  .  .  106  15 Appendix 6: Multiple correlations between vegetation structure and topographic features for the Chilcotin study area, British Columbia, 107 1991/92 . 16 Appendix 7: Multiple correlations between vegetation structure and seasonal grazing (AUMs) for the Chilcotin study area, British Columbia, 108 1991/92 . .  vi  List of Tables 1. Most common, and red- and blue-listed bird species censused in the Chilcotin study area, British Columbia, 1991/92 . .  28  2. Bird densities and Shannon’s diversity indices by study site, for the Chilcotin study area, British Columbia, 1991/92 .  29  .  .  3. Long-billed curlew breeding densities within the Chilcotin study area, British Columbia, 1990, 1991, and 1992 . . . . . . . . . . .  30  .  4. Long-billed curlew breeding densities within the Chilcotin study area, British Columbia, . 1987, 1990, 1991, and 1992 . . . . . . .  31  5. Principal components and component loadings for habitat variables in the Chilcotin . study area, British Columbia, 1991/92 . .  33  6. Mean numbers of bird/habitat correlations by general habitat characteristic for the Chilcotin study area, British Columbia, 1991/92  .  .  .  .  .  .  .  .  34  .  7. Pearson correlation coefficients for bird/habitat correlations for the Chilcotin . study area, British Columbia, 1991/92 . .  36  8. Habitat variables associated with low, medium, and high diversity of bird species in the Chilcotin study area, British Columbia, 1991/92 . . . . . . . .  .  .  .  46  9. Habitat variables associated with low and high abundances of horned larks in the Chilcotin study area, British Columbia, 1991/92 . . .  .  .  .  48  10. Habitat variables associated with low and high abundances of vesper sparrows in the Chilcotin study area, British Columbia, 1991/92 . . . 11. Habitat variables associated with low, medium, and high breeding densities of long-billed curlews in the Chilcotin study area, British Columbia, 1991/92 .  vii  50  .  .  .  .  52  12. Habitat variables associated with low, medium, and high abundances of western meadowlarks in the Chilcotin study area, British Columbia, 1991/92 . . . . . 13. Mean habitat variables associated with highest bird species diversity and species abundances in the Chilcotin study area, British Columbia, 1991/92 . . . . . . . . .  viii  54  .  .  56  List of Figures 1. Location of the study area in British Columbia  .  11  .  15  2. Location of the grassland study sites and arthropod collection sites within the Chilcotin study area, British Columbia, .  .  .  3. Cluster analysis of Shannon’s diversity indices by study site for the Chilcotin . study area, British Columbia, 1991/92  .  .  45  4. Cluster analysis of horned lark abundances by study site for the Chilcotin study area, British Columbia, 1991/92 . . . . . . . .  .  47  5. Cluster analysis of vesper sparrow abundances by study site for the Chilcotin . . study area, British Columbia, 1991/92  .  49  1991/92  .  .  .  .  .  .  .  .  .  .  .  6. Cluster analysis of long-billed curlew breeding densities by study site for the Chilcotin study area, British Columbia, • • 1991/92  51  7. Cluster analysis of western meadowlark abundances by study site for the Chilcotin study area, British Columbia, 1991/92 .  53  8. Habitat structural availability and use by horned larks, vesper sparrows, western iueadowlarks, and mountain bluebirds in the Chilcotin study area, British Columbia, 1991/92  .  .  .  .  .  .  .  .  .  ix  .  .  57  Acknowledgements I thank my research supervisor, Dr. Michael Pitt for enthusiastically supporting this project when others did not. am also grateful to Dr. Pitt for addressing my doubts and anxieties with sympathy and humour, and for teaching me the value of patience and diplomacy. Above all though, I thank Mike for offering the rare gift of friendship between supervisor and student. Dr. Jean— Special thanks also go to my committee members. Pierre Savard provided the initial idea and support for this project. Dr. Val Lemay gave generously of her time and expertise, and showed infinite patience during the data analysis. Dr. Judy Myers and Dr. Fred Bunnell provided insight and direction throughout the project. I would also like to thank Harold Armieder, Herb Langin, Brian Nyberg, Jim Young, Michaela Waterhouse, Fred Knezevich, Ross Fredell, and Derek White for their advice, and generous technical and logistic support throughout the project, and Dr. Peter Special thanks Marshall for his help with the data analysis. also go to Anna Roberts, Gina Roberts, Wayne Campbell, Ed Houeck, Peter Dryce, and the Williams Lake Naturalists fbr their wealth of knowledge about the natural history of the study area, and their willingness to share it. Steve McConnell, Ruth Van den Driessche, Colleen Bryden, and Alice Cassidy were professional and dedicated field assistants. Barry Forer offered invaluable advice and moral support throughout the project. And finally, my sincere thanks go to Chief Francis Laceese of Lynn Bonner, Grant the Toosey Indian Band, and local ranchers Huffman, Neil and Kerry McDonald, Ron and Stephanie Thomson, and Art Graves for permission to do my research on their lands. This research was funded jointly by the Ministry of Forests Old Growth/Biodiversity Fund, the Forest Resource Development Agreement (FRDA), the Ministry of Environment, Lands, and Parks Habitat Conservation Fund, and the Canadian Wildlife Service. Forestry Canada provided accommodation for the field crew. Personal funding was provided by the Natural Sciences and Engineering Research Council of Canada (NSERC). —  x  1. Introduction Graul  (1980)  suggested that the grasslands of North America  have been more severely altered by man than any other major ecosystem on the continent.  In the American Great Plains and the  Canadian prairies, 45-85% and 76-99%, respectively, of the native grassland vegetation communities have been converted to intensive agricultural practises (Kiopatek Canada 1989).  In comparison,  1979; World Wildlife Fund  for western forest types, only 1 to  5% of the native vegetation communities have been replaced (Kiopatek  1979).  In British Columbia (B.C.), probably  less than 1% of grasslands have been officially protected (T. Void, pers. comm.).  Only 9% of the historical grasslands in the  Okanagan Region remain in a relatively natural state (Redpath 1990), while less than 2% of the Chilcotin-Cariboo native The  grasslands have been preserved (J. Youds, pers. comm.).  failure to preserve representative North American grasslands may have resulted from an ignorance of their biological significance of these areas  (Hooper and Pitt 1994).  For example,  in Canada,  more than 1/3 of the birds and mammals on the 1988 COSEWIC (Committee on the Status of Endangered Wildlife in Canada)  list  are from the prairie provinces, and most of these are associated with prairie grasslands and parklands (World Wildlife Fund Canada 1989).  Approximately 27% of the species on B.C. Environment’s  Red (threatened and endangered)  and Blue (vulnerable) Lists  (1993), are associated with the Chilcotin-Cariboo grasslands (Hooper and Pitt 1994).  1  British Columbia’s grasslands are unique in Canada because they are dominated primarily by the bunchgrass, bluebunch wheatgrass (Agrovron sDicatum), which only rarely occurs east of the Canadian Rocky Mountains (Hooper and Pitt 1994).  Moreover,  B.C. ‘s grasslands represent the northern limit of contiguous bunchgrass vegetation in North America, and are distinguished from their ecological counterparts in Oregon and Washington by a greater proportion of boreal rather than austral plant species (Daubenmire 1978, Hooper and Pitt 1994).  B.C.’s grasslands are  also rather exceptional because a smaller proportion than many other grasslands in Canada has been converted to crop cultivation (Hooper and Pitt 1994). The B.C. Ministry of Environment, Lands, and Parks (B.C. Environment)  (1991) considers bunchgrass and big sagebrush  (Artemisia tridentata) habitats in the province to be major wildlife habitats of concern because: a) their area and distribution is limited; b) they are being lost to urban and agricultural development; and C)  they are being altered by livestock grazing and forest encroachment.  Despite these concerns, and the fact that B.C. Environment and the B.C. Ministry of Forests have a common goal of preserving biodiversity, there are few detailed studies of grassland fauna for British Columbia. Birds are a conspicuous and important component of grassland ecosystems (Wiens 1973b), and some species are often restricted 2  to grassland habitats (Cody 1985).  Disturbances to grasslands,  then, could affect grassland bird populations and communities. In their problem analysis on biodiversity of the Chilcotin— Cariboo grasslands, Hooper and Pitt (1994)  found that livestock  grazing was considered by grassland resource—users to be the impact of greatest concern to that region’s grasslands. Detailed studies of grassland bird communities or their habitat associations for B.C., and data that document the potential impacts of livestock grazing on British Columbia’s grassland bird populations are lacking.  In the interest of  grassland biodiversity conservation, this research was designed to address these information needs.  1.1 Literature Review 1.1.1 Grassland Bird Communities and Habitats Bird diversity and abundance are often positively correlated with vegetation complexity (Roth 1977, Cody 1985).  Because  grassland vegetation structure is fairly homogeneous, grassland bird communities are relatively simple.  In general, grasslands  are characterized by two to six passerine species, and occasionally, as many nonpasserine species (Cody 1985).  In  comparison, the mean number of bird species in coniferous forests can be two to four times greater than that of grasslands (Wiens 1975). Vegetation structure is considered to be the most important 3  factor affecting grassland bird distribution (Tester and Marshall 1961, Hilden 1965, Wiens 1969, Whittaker and Woodwell 1972, Cody 1985).  The most important components of vegetation structure for  grassland birds are grass height and/or density (Cody 1966, Creighton 1974, Ohanjanian 1985), patchiness (Wiens 1969, 1975),  1973b,  litter and vegetation  1974a,  1974b,  1976, Wiens and Dyer  and amount of ground and shrub cover (Bock  Wiens and Rotenberry (1981)  1984).  suggested, however, that birds of  shrub—steppe environments also respond to vegetation floristics. A more complete understanding of grassland avian habitat associations may, therefore, be obtained by studying both vegetation physiognomy and floristics (Wiens and Rotenberry 1981). Bird diversity can also be correlated with food availability (Wiens 1974a).  Grassland birds are omnivorous, but during the  breeding season, arthropods form the bulk of the diet (Wiens Grasshoppers, ants, beetles,  1973b, Terres 1980, Cody 1985).  bugs, butterfly and moth larvae, and spiders are the most common prey items (Wiens 1973b, Rotenberry and Wiens 1978, Cody 1985, Redmond and Jenni 1985), with grasshoppers probably being the most important arthropod in grassland bird diets (Baldwin 1971, 1973, Maher 1979).. resource,  Because food can, at times, be a limiting  food supplies may exert strong influences on bird  communities (Rotenberry 1980).  Limitations in arthropod  abundances then, could affect the composition of grassland breeding bird communities. 4  1.1.2 Influences of Livestock Grazing on Grassland Bird Conimunities and Habitats Most B.C. grasslands are managed, either privately or by the Ministry of Forests, for sustained forage and livestock production (Hooper and Pitt 1994).  Livestock grazing can change  grassland vegetation structure by altering vegetation density, plant vigour and growth, and plant community species composition (Ryder 1980).  Not surprisingly, these changes often correspond  to increases or decreases of many grassland bird species (Townsend and Smith 1977). Possibly the most important component of grassland bird habitat affected by grazing is availability of cover for nesting, rearing, hiding, and thermoregulation.  Birds that prefer to nest  in dense or tall vegetation, and/or require elevated singing perches may benefit from levels of grazing and browsing that stimulate bushier shrub growth, or that leave large amounts of standing vegetation (Ryder 1980).  For example, sharp—tailed  grouse are more likely to use dancing grounds and adjacent nest sites in areas where grazing levels maintain, rather than remove nesting and brooding cover (Pepper 1972).  Conversely, grazing  levels that reduce vegetation height and density could favour species such as the long—billed curlew which may require good visibility for communal detection of predators, and for unhampered movements of their precocial chicks when feeding (Allen 1980).  Adult horned larks also forage less efficiently in  tall, dense vegetation which can result in chicks starving to 5  death in the nest (Cody 1985). Changes in vegetation structure due to grazing can also affect the availability of cover for hiding or thermoreguiation. For example, long-billed curlews may require patchy plant distribution for camouflage since they nest in open areas without protection of overhanging vegetation (Ohanjanian 1985).  Other  species, however, need sufficient vegetative cover during warm weather to prevent water loss in eggs and heat stress to chicks. Even short—grass nesters like horned larks seem to require some taller grasses around their nests for thermal protection (Cannings 1981). Aside from grazing action, the mere presence of grazers can affect habitat structure.  For example, trampling can change  vegetation structure by killing or compacting plants and reducing competitive cover, but it can also facilitate seed dispersal (Springfield 1976, Little 1977).  Trampling can also cause soil  disturbances or compaction which can be beneficial or detrimental to ground-nesting birds which build their nests in soft soil (Harrison 1984).  Additionally, manure pies left by livestock can  increase structural variability of the habitat by providing wind breaks or camouflage for ground—nesting birds (Cameron 1907). In addition to influencing habitat structure, livestock grazing may affect grassland birds by altering food resources. Grassland arthropods can be affected by changes in microclimate, living space, and food availability as a result of grazing (Breymeyer and van Dyne 1980).  Arthropod numbers may increase, 6  but species numbers generally decline with heavy grazing (Smith 1940).  Like birds, different arthropod types respond differently  to grazing pressures.  For example, grasshoppers prefer open  grasslands with sparse vegetative cover (Hewitt  .  1974), and  thus, apparently benefit from grazing (Shotwell 1958, Skinner 1975), as they are more common in heavily grazed than lightly grazed areas (Smith 1940, Kelly and Middlekauff 1961).  In  contrast, higher densities of harvester ants (Pogonomvrmex spp.) occur in moderately rather than heavily grazed areas (Rogers 1972). These effects of grazing on arthropod distribution and abundances could be beneficial or detrimental to grassland birds depending on their dietary needs and preferences.  Additional  benefits to grassland bird food resources may be derived from livestock grazing.  Manure piles left by grazers can provide food  in the form of insects and partially digested plant matter. Long-billed curlews will probe, and horned larks will tear apart “cow pies,” presumably to retrieve seeds and insect parts, or whole insects feeding in the “pies”  (Ryder 1980).  Although the species of grassland birds have been recorded for B.C., few quantitative data are available on breeding bird diversity and density, species abundances, and habitat associations.  Few studies in the current literature have  examined the relationships among grassland birds, habitat structure, food availability, and livestock grazing. research was designed to examine those relationships. 7  This  1.2 Objectives The objectives of this research were: 1.  to characterize grassland breeding bird communities of the study area in terms of bird density, species diversity, and species abundances;  2.  to identify associations between grassland habitat characteristics and breeding bird diversity and species abundances;  3.  to determine the relationship between food resource availability and breeding bird diversity anI species abundances; and,  4.  to elucidate potential influences of livestock grazing on grassland breeding bird communities and their habitats.  Only breeding birds were considered since British Columbia’s grasslands, in general, offer too little food and shelter to support a winter bird community (Cannings  j,. 1987).  1.3 Research Hypotheses The research hypotheses and predictions tested in this study were: 1.  Vegetation structure is the primary determinant of grassland breeding bird diversity and species abundances. a)  Bird diversity will be greater in more structurally complex habitats, and will therefore,  increase with  vegetation height, vertical cover, and vertical and 8  horizontal patchiness. Individual bird species will be associated with  b)  particular vegetation structural types.  Abundances of  some species will be most strongly associated with structurally complex habitats while other species will be associated with less complex habitats (e.g., with reduced vegetation height, vertical cover, and patchiness). 2.  Grassland breeding bird diversity and species abundances are also associated with food availability. Bird diversity will be greater in areas with greater  a)  arthropod biomasses. Individual bird species will be associated with  b)  particular food resources.  Abundances of individual  species will be positively correlated with biomasses of particular arthropod types. 3.  Grassland breeding bird diversity and species abundances are affected by livestock grazing. a) The greatest influence of livestock grazing on grassland birds will be due to alterations in habitat structure. Habitat complexity will decrease with increased grazing pressure due to reduced vegetation height, vertical cover, and vertical and horizontal patchiness. i)  Bird diversity will decline with increased grazing pressure due to reduced habitat complexity.  ii)  Individual bird species will be affected differently 9  by livestock grazing. Species associated with structurally simple habitats will increase in abundance with increased grazing pressure due to reduced vegetation height, vertical cover, and vertical and horizontal patchiness.  Species  associated with structurally complex habitats will decrease in abundance with increased grazing pressure. b) Livestock grazing will also affect individual species of breeding grassland birds due to alterations in food resources.  Individual arthropod types will be affected  by livestock grazing due to alterations in habitat structure. i) Arthropod types associated with structurally simple habitats will increase in abundance with grazing pressure due to reduced vegetation height, vertical cover, and vertical and horizontal p&tchiness. Increases in abundances of certain arthropod types will be associated with increases in certain bird species.  2. Study Area The study area was the grasslands around Riske Creek 52’ N, 122° 21’ W) (Fig. 1).  (51°  in the Chilcotin Region of British Columbia  These grasslands are within the Fraser River Basin  Ecosection, and the Bunchgrass and Interior Douglas—fir 10  Fig.  1. Location of the study area in British Columbia. 11  biogeoclimatic zones (Demarchi 1988). The study area included grassland and shrub—steppe sites ranging from 585 to 1000 in elevation within the Bunchgrass (BG) and Interior Douglas-fir (IDF) biogeoclimatic zones.  Both  biogeoclimatic zones are typified by warm to hot, dry summers, and cool to cold winters with relatively little snowfall j.  (Nicholson  1991, Hope  .  1991).  Precipitation tends  to be bimodal with the main peak occurring in December and January,  and a secondary peak occurring in June (Nicholson g  1991, Hope  ,  .  1991).  Throughout the study area, the  Bunchgrass biogeoclimatic zone often intergrades into the IDF biogeoclimatic zone. Grasslands of the BG zone occur on Brown, Dark Brown, Black, and Dark Gray Chernozemic soils, and are characterized by widely— spaced bunchgrasses and a well—developed cryptogam layer (Nicholson  .  1991).  Two subzones  and the Very Dry Warm (BGxw)  -  the Very Dry Hot (BGxh)  occur from valley bottoms to about  700 iu elevation, and from about 700 to 1000 respectively (Nicholson  in  elevation,  1991).  Dominant vegetation on mesic and submesic sites within the BGxh includes bluebunch wheatgrass, big sagebrush, and Sandberg’s bluegrass (g sandbergii), while needle-and-thread grass (Stipa comata)  and sand dropseed (Siorobolus crvtandrus) dominate xeric  sites with coarse-textured soils.  Within the BGw, dominant  vegetation includes bluebunch wheatgrass, pasture sage (Artemisia frigida), and junegrass (Koeleria macrantha). 12  Rabbit-brush  (Chrysothamnus nauseosus)  is also often present, and porcupine  grass (Stipa curtiseta) and Kentucky bluegrass  (  pratensis)  occur on moist sites and on the bases of some slopes.  Mesic to  submesic sites at higher elevations of the BGxw are dominated by a porcupine grass/Rocky Mountain fescue (Festuca. saximontana) association.  Plant communities found on wetter sites above 700 in  within the BG zone include small groves of trembling aspen (PoDulus tremuloides) with understories of western snowberry (Svnrnhoricarpos occidentalis), Kentucky bluegrass, northern bedstraw (Galium boreale), American vetch (Vicia americana), quackgrass (AgroDyron repens), and star—flowered false Solomon’s— seal (Smilacina stellata)  (Roberts 1992).  Grasslands of the IDF zone occur on Orthic Dark Brown, Orthic Black, and Dark Grey Chernozems.  Dominant plant  communities include bluebunch wheatgrass, porcupine grass, spreading needlegrass (Stipa richardsonii), and Rocky Mountain fescue, with pasture sage,  junegrass, Kentucky bluegrass, and  woolly cinquefoil (Potentilla hipiana) also being common. Timber milk-vetch (Astragalus miser), yarrow (Achillea millefolium), cheatgrass (Bromus tectorum), cut—leaved daisy (Ericeron coinpositus), yellow-rattle (Rhinanthus crista-aalli), and goats—beard (Tragopocron spp.) can also become common with increased livestock grazing pressure (Hope  13  j,. 1991).  3 Methods 3.1. Study Sites  Thirteen grassland study sites were established within an area bounded by the Junction Wildlife Management Area (WMA), Becher’ s Prairie, and the Fraser River (Fig. 2).  Study sites  were selected to represent regional variability in topographic Sites were chosen then, based on  and vegetation characteristics.  differences in elevation, slope, aspect, and early spring (April) vegetation height and vertical cover.  Differences in vegetation  height and cover were used as indicators of levels of grazing pressure.  Sites were also selected for their accessibility by  vehicle, and for their size (i.e., sites had to be large enough to accommodate at least four bird census points).  3.2 Grassland Breeding Bird Censuses  3.2.2. Species Censuses Birds were censused using the point—count method (Verner 1985).  Points had a radius of 100 m and were placed at least 300  m apart, as measured from the centre of each point.  Although  some edge habitat was included in some points, areas with large or dense stands of trees, or large wetlands were avoided.  Four  to 15 points (determined by grassland area) were established in each of the 13 grassland sites (145 points total)  (Hooper and  Savard 1991). All points were established as semi—circles along roadways through the sites.  The observer drove to the centre of 14  Bedie?s Pralde It  E17 u ‘8..E  • ———-——.——-..  .‘Hvy2O  E’.  \  .BW % — —  —  —  -  tQ/%.  —  I  M_SE  • • T_N Toosey ênckn Reseve •T_S  I  ii ____M_NE\%, I ç•M_NW MdonaIds Randi  )  .0 Deer Paik Ranch  /  ———pavedmad  s_s  . . -. .  -  dkt road  ••S..SW  Junclon WMA  N I  0  Fig. 2.  gravel .oed  —I 2.5  Location of the grassland study sites (.) and arthropod collection sites (U) within the Chilcotin study area, British Columbia, 1991/92. 15  a point, turned of f the vehicle, got out and quietly closed the door, then waited two minutes before beginning the count.  This  method was used to avoid disturbing birds by walking through the Counts were made for  point—count area (Hooper and Savard 1991).  three consecutive four—minute periods at each point (12 minutes total per point).  All birds detected within the point-count  circle, and up to 50 m beyond the circle were recorded.  Each  point was surveyed between 05:30 a.m. and 10:00 a.m., five or six times between early May and early July (the height of the bird breeding season), in each of 1991 and 1992. Bird species diversity per grassland site was calculated using Shannon’s diversity index: H’= -E p 1 1 log p  (where p. is the  proportion of all observations of the ith species and i=1,2,...S (where S is the total number of species))  (Magurran 1988).  Bird  density per site was calculated as the total number of birds divided by the total area censused.  The area of the 100-rn radius  point count semi—circle, plus the 50—rn radius border beyond the circle was 3.92 ha (Hooper and Savard 1991).  To compare density  estimates with other grassland bird studies, the number of birds per hectare was divided by 1.5 to give an estimate of number of pairs of birds per hectare. Bird common and taxonomic names were taken from the American Ornithological Union Checklist pj North American Birds (1983) and recent supplements (1984; 1985; 1987; 1989).  16  3.2.2 Long—billed Curlew Censuses Because 100—rn radius point—counts may not adequately census long—billed curlews (Hooper and Savard 1991), a modified spotmapping technique was also used.  Observers drove along roadways  within the 13 study sites and recorded the number and sex of long—billed curlews observed.  Each site was surveyed 3—5 times  during April and May in each of 1991 and 1992, when curlews were establishing and defending territories.  The repeated surveys  documented individual breeding territories.  Curlew breeding  densities were determined as the number of territories divided by total grassland area for that site.  3.3 Habitat Characteristics 3.3.1 Vegetation Structure Height and Vertical Cover Height of herbaceous vegetation was measured as the height (cm)  at which the vegetation was most dense, based on an  observer’s eye height of 30 cm, at a distance of 10 m from the meter stick (Hooper and Savard 1991).  Vertical cover  (%)  of  herbaceous vegetation was measured using a 30— x 50—cm vision board, with an observer eye height of 30 cm, at a distance of 10 m from the board (Bicak  j,.  1982, Hooper and Savard 1991).  Five samples of height and vertical cover were taken within the circumference of each point—count circle, again in late June,  in each of 1991 and 1992  /site/year depending on site area). 17  in early May and (n  =  40—150  A random numbers table was  used to locate individual sample points at a specific distance and direction from the centre of the point—count circle. Vegetation height and vertical cover were measured in both May and June to determine if species site associations were based on habitat requirements for breeding (i.e., (i.e.,  in May)  or for rearing  in June).  Horizontal Cover The frequency and horizontal cover  (%) of nine physiognomic  features were measured using a 20— x 50—cm Daubenmire frame. Physiognomic features assessed were grasses, trees, cryptogams, rocks, bare soil,  forbs, shrubs,  litter, and animal feces.  Percent cover was recorded according to cover class: class 0: 0% cover,  1:  95—100%.  1—5%,  2: 5—25%,  3: 25—50%,  4: 50—75%, 5: 75—95%, and 6:  Mid—points of each cover class were used as cover  values in the data analyses.  An area considered representative  of the site’s dominant plant community was used for sampling.  If  more than one type of plant community dominated a site, sampling was done in each community.  In each plant community, three 50—m  transects were laid parallel with the land contours, with 30 m between transects.  Ten samples were taken along each transect.  All transects were at least 50 m from any roads to avoid disturbance effects.  A random numbers table was used to locate  sampling points along the transects. mid-June,  in each of 1991 and 1992.  Measurements were made in These sampling methods were  consistent with those used by the B.C. Ministry of Forests (H.  18  Armieder, F. Knezevich, pers. comm.).  Vegetation Patchiness Vegetation patchiness was assessed using heterogeneity indices for vegetation height and vertical cover, and horizontal cover of bare ground.  Indices were calculated by dividing the  range of measurements of the attribute, by the mean, point (Rotenberry and Wiens 1980).  for a given  These indices were chosen so  as to be consistent with the those used by Rotenberry and Wiens (1980).  3.3.2 Vegetation Species Composition The frequency and horizontal cover  (%) of plant species was  measured using a 20— x 50—cm Daubenmire frame. recorded according to cover class: class 0: 5—25%,  3:  25—50%,  Percent cover was  0% cover,  1:  4: 50—75%, 5: 75—95%, and 6: 95—100%.  1—5%, 2: Mid  points of each cover class were used as cover values in the data analyses.  An area considered representative of the site’s  dominant plant community was used for sampling.  If more than one  type of plant community dominated a site, sampling was done in each community.  In each plant community, three 50—rn transects  were laid parallel to the land contours, with 30 m between transects.  Ten samples were taken along each transect.  All  transects were at least 50 m from any roads to avoid disturbance effects.  A random numbers table was used to locate sampling  points along the transects.  Measurements were rn.ade in mid—June,  19  in each of 1991 and 1992.  These sampling methods were consistent  with those used by the B.C. Ministry of Forests (H. Armleder, F. Knezevich, pers. comm.). Plant common and taxonomic names were taken from Taylor and MacBryde (1977), Meidinger (1987), and Douglas  (1989,  1990, 1991).  3.3.3 Pood Resources Food resources were measured in terms of arthropod abundances.  Pan traps were used to collect both low—flying and  ground-crawling arthropods (Martin 1977, Hooper and Savard 1991). Five traps were set in each of six grassland study sites (30 traps total)  (Fig. 2).  Three sites were ungrazed or lightly  grazed, while the other three sites were more heavily grazed. Each trap was set at a point—count location, and traps were located equi-distant throughout the site. mid-April to late June, analysis,  Traps were set from  in each of 1991 and 1992.  In the data  36 rather than 30 sites had arthropod data, because one  site and one sampling point had to be changed between years due to livestock disturbances. Traps were made from 23 x 23 x 4—cm cake pans buried to the rim and filled about 2/3 full with water and dishwashing detergent. 450  A 30.5 x 30.5-cm board was placed at approximately  over the pan.  Arthropods were removed from the traps by  filtering the trap contents through a small aquarium net. contents were returned to the traps and replenished, if 20  Liquid  necessary.  Arthropods were collected weekly and stored in 10%  isopropyl alcohol until identified.  Samples were discarded if  the traps had been disturbed by livestock. Arthropods were counted and identified by broad groupings: ants: large (6 mm) or small (5 mm), bees: large (lO mm) or small (9 mm), beetles: large (16 mm), medium (10—15 ram), or small (9 mm), bugs: large (6 mm) or small (5 mm), flies: large (6 mm) or small (5 mm), grasshoppers: large (15 mm), medium (10—15 mm), or small (9 mm), larvae: large (15 mm) or small (14 mm), butterflies/moths: large (ll mm) or small (l0 mm), spiders: large (l0 mm), medium (6—10 mm), or small (5 mm), and others.  These groupings were chosen because ants, beetles, bugs,  butterfly and moth larvae, grasshoppers, and spiders are the most common prey items of breeding grassland birds (Rotenberry and Wiens 1978, Cody 1985, Redmond and Jenni 1985).  Flies and bees  were included in this analysis because they were commonly collected. Arthropods were oven—dried to constant weight at 60° C, and weighed on a Mettler AC 100 electronic balance to 0.0001 gin (Southwood 1978).  Biomass estimates were then made for ants,  bees, beetles, bugs, flies, grasshoppers, larvae, moths and butterflies, spiders, and total arthropods.  3.3.4 Grazing Information To assess the potential impact of grazing on grassland bird communities on the 13 study sites, information on the season, 21  intensity, and duration of grazing by livestock (cattle and horses) and California bighorn sheep (Ovis canadensis californiana) was gathered from ranchers, Ministry of Forests agrologists, and B.C. Environment wildlife biologists.  Number of  Animal Unit Months (AUM5) was then calculated by season for each site.  The definition of AUM used in this study was the amount of  forage required to feed a mature cow, with or without suckling calf, for one month.  AUMS were calculated based on the metabolic  weight of a 454 kg cow. 1.3 AUMs.  Grazing by one horse was equivalent to  Using a weight of 68 kg for a bighorn sheep ewe (Burt  and Grossenheider 1976), grazing by one bighorn sheep was Animal Unit Months were used to  equivalent to 0.25 AUMS.  quantify grazing levels so as to be consistent with Ministry of Forests grazing assessment methods.  3.3.5 topographic Features Slope, aspect, elevation, and soil bulk density were recorded as additional site descriptors for each of the 13 sites. Slope was measured using an Abney level; aspect was determined using a hand—held compass.  Elevation was taken from Department  of Energy, Mines, and Resources 1:50,000 topographic maps with 50 m contour intervals.  Soil bulk density was measured to assess  degree of soil compaction, which may be important to ground— nesting birds that build nest scrapes. with a 2” Dutch auger.  Soil cores were removed  The hole’s volume was measured by lining  the hole with a plastic bag and filling it with a measured amount 22  1000  C and  weighed on a Mettler PC 4400 electronic balance to 0.01 gm.  Soil  of water.  Soil cores were dried to constant weight at  bulk density was estimated as the ratio of soil weight to water volume.  One soil sample was collected at each point—count  location (n=145 samples).  A random nuLlbers table was used to  locate the distance and direction of sampling points from the centre of the point—count circle.  3.4 Habitat Structure Use by Birds To clarify the importance of habitat structural features to grassland birds, the use of various structures by mountain bluebirds, western meadowlarks, vesper sparrows, and horned larks for displaying, resting, and feeding was recorded during the point—count censuses.  These species were selected because they  were among the most common grassland bird species (Hooper and Savard 1991), and because they were more commonly observed using structural features than other species.  The measurements of  physiognomic features covered only a small portion of each study site, and thus, may have underestimated the numbers of some structural features important to grassland birds; consequently, additional counts were made of rocks, shrubs, trees, fences, logs, and roads (i.e •, narrow gravel roads and dirt tracks), both on, and 50 m beyond each point—count circle.  23  3.5 Statistical Analyses Analyses were initially done separately for each of the field seasons. Because results were similar between years, however, the data were combined and re—analyzed to give trends in bird habitat associations across the two field seasons.  Data  from the 1991 and 1992 field seasons then, were combined, and means of the bird and habitat variables were calculated for each of the 145 points used to census birds.  The bird diversity  indices, and measures of the physiognomic classes which were made per site rather than per point, were simply repeated for each of the points within the site.  Missing values were given for sites  and points without arthropod variables. Data reduction of the habitat variables was done using principal components analysis (PCA) on SYSTAT (Version 5.02, 1991).  Because the data set was too large to analyze with the  personal computer version of SYSTAT, the habitat variables were split into two files.  One file included the vegetation  structure, topographic, and grazing data, while the second file included the vegetation species composition data.  The arthropod  variables were not included because data were available for only 36 of the 145 points.  Because there were only 10 arthropod  variables, data reduction by PCA was unnecessary. Principal components were selected based on eigenvalues of the correlation matrix that were greater than one.  Component  loadings ‘t0.6O0I were chosen to select variables for further analysis. 24  Following PeA, multiple correlations identified associations between the habitat variables and Shannon’s diversity indices, the most common bird species (i.e., those specie comprising >1% of all observations), and those species on B.C. Environment’s Red— and Blue—lists (1993).  Red crossbills, European starlings,  and American crows were among the most common species recorded, but were excluded from the correlation analyses.  Crossbills were  excluded because they are a forest—dwelling species and were only recorded flying over the plots.  Starlings and crows were  excluded because they are broad habitat generalists, and not of current management interest. Multiple correlations were done using SAS (Version 6.07, 1989), since the necessary SYSTAT module for performing the analysis was not available.  A disadvantage of using SAS,  however, was that it did not make pairwise comparisons for cases with missing variables.  This was a concern, as only 36 of the  145 cases had arthropod biomass data.  Separate multiple  correlations then, were done for bird and arthropod data. Although possible associations between habitat variables and arthropods may have been overlooked, it was believed that greater information regarding bird and habitat associations would be retained if the arthropod data were analyzed separately. Although SAS provided Pearson correlation coefficients, no tests of significance were made because the data were not multivariate normally distributed, and because this study was structured to be descriptive rather than predictive. 25  Pearson  correlation coefficients >0.200 were selected to identify those habitat variables most strongly associated with the bird variables. Following the correlation analyses, cluster analyses were used to create general management guidelines for grassland bird habitats.  Cluster analyses were done using Euclidean distance  measures.  The single linkage method was used for clustering the  species diversity index, while the complete linkage method was used for the most common ground—nesting species  (i.e., long—  billed curlews, horned larks, vesper sparrows, and western meadowlarks).  Only ground—nesting species were used to develop  the management guidelines, as these birds were considered most vulnerable to potential grassland disturbances,  Study sites were  clustered based on similarities in curlew breeding densities and in abundances of the other species.  Means of the habitat  variables associated with the bird variables (as identified by the correlation analyses) were then calculated for each cluster of study sites.  Heterogeneity indices and arthropod variables  were not included in the analyses because of the perceived difficulty in trying to manage for these characteristics.  SYSTAT  was used to perform the cluster analyses. Numbers of upland sandpipers and Sprague’s pipits were too low to be used effectively in cluster analyses, so overall means of the habitat variables associated with these species were calculated for the sites in which the species were recorded. Guidelines were not determined for sharp—tailed grouse or short— 26  eared owls, even though they are ground—nesters.  Sharp—tailed  grouse were not strongly associated with any of the habitat variables measured in this study, and short—eared owl numbers were very low and their populations so variable (pers. obs.) that meaningful guidelines could not be formulated. Additional statistical analyses of the data were done using chi—square tests and paired-sample, 2—tailed t—tests.  T-tests  were done with SYSTAT and were used to test for differences in A chi—square analysis of  curlew population means between years.  a 4 x 6 contingency table was used to test the nill hypothesis that there was no difference in habitat structural use among bird species.  Chi—square analyses were also used for individual bird  species to test the null hypotheses that there was no difference between availability of structural types and use by a given species.  A significance level of a  =  0.10 was used for the t—  tests and chi—square tests.  4 Results 4.1 Bird Censuses  Ninety-nine species and 13,584 individual birds were recorded during the point—count censuses. common  —  horned lark and vesper sparrow.  Two species were very Another nine species  were relatively common (i.e., >1% of all observations): European starling, western meadowlark, long—billed curlew, Brewer’s blackbird, tree swallow, mountain bluebird, American crow, savannah sparrow, and red crossbill (Table 1). 27  Three red—listed  species  (upland sandpiper, Sprague’s pipit, and Brewer’s  sparrow), and two blue-listed species in addition to the longbilled curlew were recorded (sharp—tailed grouse and short—eared owl)  (Table 1).  A complete list of all bird species censused is  given in Appendix 1.  Table 1.  Most commona, and red— and blue—listed bird species censused in the Chilcotin study area, British Columbia, 1991/92. Total observations  % total observations  4581 3465 933 860 650 365 308 298 227 157 156  33.7 25.5 6.9 6.3 4.8 2.7 2.3 2.2 1.7 1.2 1.1  Red-listed species Upland sandpiper Sprague’s pipit Brewer’s sparrow  12 16 7  0.1 0.1 0.1  Blue—listed species Sharp-tailed grouse Short-eared owl  69 47  0.5 0.3  12,151  89.5  Common name Most common species Horned lark Vesper sparrow European starling Western meadowlark Long—billed curlewb Brewer’s blackbird Tree swallow Mountain bluebird American crow Savannah sparrow Red crossbill  Total d  b  >1% of total observations. Blue—listed species.  28  Bird densities for the 13 study sites, ranged from 1.09 to 1.65 pairs/ha, while species diversity indices ranged from 0.71 to 1.38  (Table 2).  Bird densities and Shannon’s diversity indices by study site, for the Chilcotin study area, British Columbia, 1991/92.  Table 2.  Study site  Shannon’s diversity  Density  B_E B_W C D J M_NE M_NW M_SE S_N S_SE S_SW T_N T_S  # pairs/ha  index  1.65 1.55 1.09 1.37 1.31 1.60 1.33 1.53 1.47 1.51 1.41 1.24 1.64  0.87 1.38 1.00 0.92 0.97 0.76 0.75 0.75 0.78 0.91 0.71 1.08 0.78  4.2 Long—billed Curlew Breeding Densities Densities of breeding curlews were consistent from 1990 to 1992 on most sites, but were higher in 1992 than the previous years on McDonald’s Ranch-NW (P sites of the Toosey Reserve (P  0.05), and the north and south  =  =  0.06, P  =  0.10))  (Table 3).  Compared to those areas surveyed by Ohanjanian (1987), curlew breeding densities were lower in 1990 and 1992  (P  <  0.09)  than in 1987  29  (P  =  (Table 4).  0.05),  1991 (P <0.08),  Table 3.  Long-billed curlew breeding densities within the a, 1991, Chilcotin study area, British Columbia, 1990 and  b 1992  Breeding pairs  I pairs/  I ha/  100 ha  pair  1990 1991 1992  3 2—3 3  0.2 0.1—0.2 0.2  555 555—833 555  395  1990 1991 1992  1—2 1—2 2  0.3—0.5 0.3—0.5 0.5  198—395 198—395 198  MNE  288  1990 1991 1992  4 5—6 3—4  1.4 1.7—2.1 1.0—1.4  72 48—58 72—96  MNW  292  1990 1991 1992  5—8 5 10  1.7—2.7 1.7 3.4  37—58 58 29  M SE  133  1991 1992  1 1  0.8 0.8  133 133  1141  1990 1991 1992  6—11 10—11 7—9  0.5—1.0 0.9—1.0 0.4—0.8  104—190 104—114 127—163  TN  687  1990 1991 1992  3 4—5 6—7  0.4 0.6—0.7 0.9—1.0  229 137—172 98—115  TS  401  1990 1991 1992  1 2 4  0.3 0.5 1.0  401 201 100  5003  1990 1991 1992  23—32 30—35 37—40  0.5—0.6 0.—0.7 0.7—0.8  156—218 143—167 125—135  area (ha)  Year  D  1666  J  Site  S_N/S_SWC  Total  b C  Hooper and Savard (1991). No curlews were recorded on B E, B W, C, or S_SE 1990—1992, or M_SE 1990. Sites were combined since the pasture was continuous between the two sites.  30  Table 4. Long-billed curlew breeding densities within the b, a, 1990 1987 Chilcotin study area, British Columbia,. 1991, and 1992. Area Year (ha)c  Breeding pairs  # Pairs! 100 ha  I ha! pair  Junction  410  1987 1990 1991 1992  3 1—2 1—2 2  0.7 0.2—0.5 0.2—0.5 0.5  137 205—410 205—410 205  Pass Pasture  474  1987 1990 1991 1992  7—8 2—4 5 4—5  1.5—1.7 0.4—0.8 1.1 0.8—1.1  59—68 119—237 95 95—119  South Fraser Field  470  1987 1990 1991 1992  10 1 0 0  2.1 0.2 0 0  47 470 0 0  McDonald’s Ranch NE & NW  575  1987 1990 1991 1992  20 9—12 11—12 13—14  3.4 1.6—2.1 1.9—2.1 2.3—2.4  29 48—64 48—52 41—44  Total  1929 1987 1990 1991 1992  40—41 13—19 17—19 19—21  2.1 0.7—1.0 0.9—1.0 1.0—1.1  47—48 102—148 102—114 92—102  Site  —  a from Ohanjanian b C  (1987) from looper and Savard (1991) area estimates from Ohanjanian (1987)  31  4.3 Bird/Habitat Associations 4.3.1 Principal Component Analysis  Nine principal components had eigenvalues >1.0, and these accounted for 80% of the variability in the habitat variables (Table 5).  The first three, and the ninth components had  variables with component loadings  >  0 • 600:.  Twenty of the 32  habitat variables were retained from these four components.  The  first component represented vegetation structure as measured by height and vertical cover, horizontal cover of different physiognomic features, and horizontal patchiness.  The second  component represented topographic features and vegetation structure in terms of vertical patchiness and horizontal cover of shrubs.  The third component included one topographic feature,  and the grazing variables, while the ninth component was associated vegetation structure as measured by the number of trees in the point—count area.  32  Table 5.  Principal components and component loadings for habitat variables in the Chilcotin study area, British Columbia, 1991/92.  pc Eigenvalue % variance % total variance  1 6.81 21.3  2 5.69 17.8  3 3.36 10.5  9 1.06 3.3  21.3  39.1  49.6  80.0  Habitat variableb structure Height/vertical cover MAYVGCOV MAYVGHT JUNVGCOV JUNVGHT Horizontal cover BAREGRND GRASS LITTER TREES SHRUBS Horizontal patchiness BGRNDHI Vertical patchiness MAYCOVHI MAYHTHI JUNHTHI Additional structural features TREES_O VMt4 nri  -0.763 -0.752 -0.718 -0.610 0.807 —0.611 -0.787 —0.703 0.805 -0.837 0.648 0.666 0.712  0.723  Topographic features ELEV SLOPE ASPECT  —0.773 0.866 0.659  Grazing characteristics SPRNGAUM SMMERAUM FALLAUM  0.692 0.761 0.813  Principal component b Habitat variable codes given in Appendix 2.  33  4.3.2 General bird/habitat correlations  The vegetation species composition data were excluded from the correlation analyses because a high degree of correlation and linear relationship among plant species greatly confounded the analysis.  A list of plant species recorded on the study sites,  however, is provided in Appendix 3. Topographic features and arthropods had greater mean numbers of correlations with bird diversity and species than did vegetation structure or grazing levels (Table 6).  Table 6.  Mean number of bird/habitat correlations by general habitat characteristic, for the Chilcotin study area, British Columbia, 1991/92.8  Habitat characteristic  No. variables/ characteristic  ,b  n  Vegetation structure  3.9  54  14  Topography  6.3  19  3  Grazing  2.7  8  3  Arthropods  5.3  48  9  8  results from long—billed curlew point—counts were excluded.  b total number of correlations divided by the number of variables  representing that habitat characteristic.  Multiple correlations revealed that vegetation structure, topographic features, and grazing characteristics combined, explained 15-96% of the variability in bird diversity and species abundances (Table 7).  Greatest variability was accounted for in  long—billed curlew breeding densities, followed by species 34  diversity, and abundances of western meadowlarks, vesper sparrows, Brewer’s sparrows, Sprague’s pipits, Brewer’s blackbirds, horned larks, long—billed curlew numbers from point— counts, savannah sparrows, short—eared owls, mountain bluebirds, upland sandpipers, tree swallows, and sharp—tailed grouse (Table 7). Arthropod biomasses accounted for 15—72% of the variability in the bird diversity and species abundances (Table 7).  Greatest  variability was accounted for in upland sandpipers, followed by mountain bluebirds, long-billed curlew breeding densities, savannah sparrows, species diversity, vesper sparrows, long— billed curlew numbers from point—counts, sharp—tailed grouse, Sprague’s pipits, western meadowlarks and horned larks, short— eared owls, tree swallows, and Brewer’s blackbirds.  Five of  these bird variables, however, had only, or mainly, negative associations with arthropod biomasses  —  long—billed curlew  numbers, Sprague’s pipits, western meadowlarks, horned larks, and Brewer’s blackbirds, while tree swallows showed no correlations with arthropods (Table 7).  Only three species were positively  associated with total arthropod biomass  —  mountain bluebirds, and upland sandpipers.  35  vesper sparrows,  Table 7. Pearson correlation coefficients for bird/habitat correlations, for the Chilcotin study area, British Columbia, 1991/92. Bird diversity (H) Habitat H characteristica Vegetation Structure Height/Vert. cover MAYVGCOV 0.35 MAYVGHT 0.32 JUNVGCOV 0.31 JUNVGHT 0.22 Patchiness JUNHTHI BGRNDHI Horizontal cover GRASS —0.22 SHRUBS Topography ELEV ASPECT 0.45 SLOPE Grazing SPRNGAUM —0.23 SMMERAUM FALLAUM variability explained  85%  Arthropods ANTS 0.20 BEES —0.35 BEETLES BUGS 0.21 GRASSHOPPERS -0.20 LARVAE —0.35 MOTHS —0.21 SPIDERS TOTAL BIOMASS variability explained  49%  HOLA  VESP  —0.32 —0.31 —0.41 —0.40  0.50 0.41 0.46 0.34  and species LBCU°  —0.31 —0.27 —0.33. —0.22  LBCU_denc  —0.47 —0.43 —0.48 —0.37  -0.23 -0.26  0.23 —0.20  —0.31 —0.33 0.29 —0.40 —0.37  0.53  —0.32  —0.22  0.21 —0.70 —0.38  0.21  —0.23  —0.24 -0.39 —0.41  39%  58%  38%  96%  —0.21 —0.22  0.31 0.26  —0.24  —0.33  0.31  0.49  —0.36 -0.21  —0.29  0.21 44%  36%  56%  0.26  —0.25 —0.37  27%  Bird species, habitat characteristic codes given in Appendix 2.  b based on point—count censuses. C  based on spot—mapping censuses  (i.e., breeding densities). 36  Table 7.  cont. Bird species  WEME Habitat characteristic Veetat ion Structure Height/ Vert. cover MAYVGCOV MAYVGHT JUNVGCOV JUNVGHT Patchiness MAYCOVHI MAYHTHI JUNHTHI Horizontal cover BAREGRND GRASS LITTER SHRUBS TREES TREES_O Toorahv ELEV ASPECT SLOPE Grazing SNNERAUM FALLAUM variability explained Arthropods ANTS BEES BEETLES FLIES GRASSHOPPERS LARVAE MOTHS SPIDERS TOTAL BIOMASS variability explained  BRBI  TRES  MOBL  SAVB  0.34 0.34 0.43 0.42 0.32 0.30 0.31  0.26  —0.23 —0.24  0.22 —0.24 0.27 0.66  0.50 0.20  —0.63 0.21 0.68  0.27 0.20  —0.45  0.27  0.43  —0.27 0.30 0.26  —0.20 74%  17%  40%  26%  35%  —0.23 —0.32  —0.25 -0.21 —0.27 —0.26  0.34 0.2  —0.33 0.58 0.37 0.33  —0.28 -0.21 27%  19%  15%  37  64%  —0.31 —0.30 —0.35 —0.28  50%  Table 7. cont. Bird species Habitat characteristic Vegetation Structure Patchiness MAYCOVHI MAYHTHI BGRNDHI Horizontal cover BAREGRND GRASS LITTER SHRUBS TREES Topography ELEV ASPECT SLOPE variability explained Arthropods ANTS BEES BEETLES FLIES GRASSHOPPERS LARVAE MOTHS SPIDERS TOTAL BIOMASS variability explained  UPSA  BRSP  SPPI  STGR  SEOW  0.22 0.31 0.35  —0.38 0.24 0.37  —0.44 0.40 0.21 0.26  0.21 0.64  0.32  -0.34 -0.24 0.28  0.34 20%  57%  49%  15%  29%  —0.24 0.28  0.29 0.35 0.57 0.66  0.24  0.20  0.26 0.32  0.30 0.44 0.41 72%  —c  30%  C  20%  arthropod collections were not made on the sites where BRSP were recorded.  38  4.3.3 Specific bird/habitat correlations Species Diversity Habitat and arthropod variables accounted for 85% and 49% of the variability in species diversity, respectively.  Diversity  increased with aspect and was greatest on sites with tall, dense vegetation, low grass cover, and low levels of spring grazing. Diversity was also greatest on sites with high ant and bug biomass, and low bee, grasshopper, larva, and moth biomass (Table 7).  Horned Lark Thirty-nine percent and 27% of the variability in horned lark numbers was accounted for by the habitat and arthropod variables, respectively.  Horned larks were most abundant on  gently sloping, high-elevation sites with low aspect.  Larks were  also most common on sites with short, open vegetation, low shrub cover, and reduced patchiness of June vegetation height.  Horned  larks were not positively associated with any of the arthropod types (Table 7).  Vesper Sparrow Habitat variables explained 58% of the variability in vesper sparrow abundance,  Vesper sparrows were most common on sites  with high aspect, tall, dense vegetation, and low grass cover. Sparrow numbers also increased with fall grazing levels. Arthropod variables accounted for 44% of the variability in 39  vesper sparrow abundance.  Sparrow numbers increased with beetle,  bug and total arthropod biomass, but declined on sites with high larva biomass (Table 7).  Long-billed Curlew Habitat variables accounted for 38% of the variability in long-billed curlew numbers based on point-counts, but 96% of the variability of curlews based on breeding densities.  Curlews were  most common on gently sloping, high-elevation sites with low aspect.  Curlews were also most abundant on sites with short,  open vegetation, low shrub cover, high grass cover, and reduced Curlew numbers declined as grazing  patchiness of bare ground. levels increased.  Arthropod variables accounted for 36% and 56% of curlew numbers and breeding densities, respectively.  Curlews were most  abundant in areas with high bee and larva biomass, and least abundant on sites with high spider and total arthropod biomass (Table 7).  Western Meadowlark Seventy-four percent and 27% of the variability in western meadowlark numbers was explained by the habitat and arthropod variables, respectively.  Meadowlarks were most common on steep,  low elevation sites with high aspect.  Meadowlarks were also most  abundant on sites with tall, dense, patchy vegetation, and high shrub cover.  Meadowlark numbers declined with declines in fall 40  grazing levels and larva biomass (Table 7).  Brewer’s Blackbird Habitat and arthropod variables accounted for 40% and 15% of variability in Brewer’s blackbird numbers, respectively. Blackbirds were most abundant on steep, low elevation sites with high shrub cover and patchy vertical cover of May vegetation. Brewer’s blackbirds were not positively associated with any arthropod groups (Table 7).  Tree Swallow Only 17% of the variability in tree swallow abundance was attributed to the habitat variables.  Tree swallows were most  common on sites with high tree cover and low patchiness of vegetation vertical cover in May.  Although the arthropod  variables, as a whole, explained 19% of the variability in tree swallow numbers, no strong associations between swallows and individual arthropod types were identified (Table 7).  Mountain Bluebird Habitat variables explained 26% of the variability in mountain bluebird abundance.  Bluebird numbers were greatest on  gently sloping, high-elevation sites, with high tree and litter cover, and low patchiness of June vegetation height. accounted for 64% of variability in bluebird numbers.  Arthropods Mountain  bluebird abundance increased with beetle, grasshopper, moth, 41  spider, and total arthropod biomass, but declined as ant biomass increased (Table 7).  Savannah Sparrow Habitat and arthropod variables accounted for 35% and 50% of the variability in savannah sparrow numbers, respectively. Sparrows were most common on sites with low gra&s cover and high bare ground cover, and numbers increased with summer and fall grazing levels.  All correlations between sparrows and arthropods  were negative (Table 7).  Upland Sandpiper Twenty per cent and 72% of the variability in upland sandpiper abundance was attributed to the habitat and arthropod variables, respectively.  Sandpipers were found on sites with  high grass, litter, and tree cover, but low and patchy coverage of bare ground.  Sandpiper numbers also increased with all  arthropod types except larvae (Table 7).  Sprague’s Pipit Habitat and arthropod variables explained 49% and 30% of the variability in Sprague’s pipit abundance.  Pipits were found on  sites with low aspect, high grass and litter cover, and low bare ground cover.  Sprague’s pipits were not positively associated  with any arthropod group (Table 7).  42  Brewer’s Sparrow Fifty—seven percent of the variability in Brewer’s sparrow abundance was explained by the habitat variables.  These sparrows  were common on steep sites with patchy vertical vegetation, and high shrub and tree cover (Table 7).  Sharp-tailed Grouse The habitat variables as a whole, accounted for 15% of the variability in sharp-tailed grouse numbers, but no strong associations with individual habitat characteristics were found. Arthropods explained 33% of the variability in grouse abundance, with grouse being most common on sites with high bee, fly, and moth biomass (Table 7).  Short-eared Owl Habitat and arthropod variables accounted for 29% and 20% of the variability in short—eared owl numbers, respectively.  Owls  were abundant on steep, low—elevation sites with high shrub cover.  Short—eared owl numbers also increased with fly and moth  biomass (Table 7).  4.3.4 Species Management Guidelines  Species Diversity The cluster analysis separated the species diversity indices into three groups associated with low, medium, and high species 43  diversity (Fig.  3).  Trends in habitat associations identified by  cluster analysis (Table 8) were similar to those of the correlation analysis (Table 7).  Highest species diversity was on  sites with south-facing aspects and no spring grazing, and with average May/June vegetation height of 9-13 cm, vegetation vertical cover of 36—44%, and grass cover of 29%.  Horned Lark The cluster analysis separated horned larks into two groups associated with low and high abundance (Fig. 4).  Trends in  habitat associations identified by cluster analysis (Table 9) were similar to those of the correlation analysis (Table 7). Highest numbers of horned larks were on east—facing sites averaging 939 m elevation, with slope of  40  May/June vegetation  height of 6-10 cm, vegetation vertical cover of 21-30%, and shrub cover of 0.10%.  Vesper Sparrow The cluster analysis separated vesper sparrows into two groups associated with low and high abundance (Fig. 5).  Trends  in habitat associations identified by cluster analysis  (Table 10)  were similar to those of the correlation analysis (Table 7). Highest numbers of vesper sparrows were on south—west—facing sites with average May/June vegetation height of 8-12 cm, vegetation vertical cover of 32—41%, grass cover• of 33%, and fall grazing levels averaging 548 AUMs. 44  Site  BW  ()High  TN  D  Medium  1  S_SE B_E  ‘1  I  T_S SN  MNET t Ii Low MNW M_SE SSW  I  I  0.1  0.2  0.3  0.4  0.5  Euclidean Distance  Fig. 3.  Cluster analysis of Shannon’s diversity indices by study site for the Chilcotin study area, British Columbia, 1991/92. 45  Table 8.  Mean habitat variables associated with low, medium, and high diversity of bird species in the Chilcotin study area, British Columbia, 1991/92. Species diversity  Habitat variableb MAYVGCOV (%) MAYVGHT (cm) JUNVGCOV (%) JUNVGHT (cm) GRASS (%) ASPECT (°) SPRNGAUM a  Low  Medium  High  (0.71—0.78)  (0.91—1.08)  (1.38)  30 8 42 13 35 210 541  20 6 30 10 39 103 507  Shannon’s diversity index (H).  b Habitat variable codes given in Appendix 2.  46  36 9 44 13 29 192 0  Site  I  D’J  ___L I  C  I T_N J  I  s_sw  I  B_E  High  MNW  [__  I  I  T_S M_SE}  MNE  \ I  I 1  3  2  •i  4  Euclidean Distance  Fig. 4.  Cluster analysis of horned lark abundances by study site for the Chilcotin study area, British Colimthia, 1991/92. 47  Table 9.  Mean habitat variables associated with low and high abundances of horned larks in the Chilcotin study area, British Columbia, 1991/92. Horned lark abundance  Habitat variablea MAYVGCOV (%) MAYVGHT (cm) JUNVGCOV (%) JUNVGHT (cm) SHRUBS (%) ELEV (in) ASPECT (°) SLOPE (°) d  Low (0.15—1.71) 33 9 45 12 0.60 818 211 9  High (3.13—5.06) 21 6 30 10 0.10 939 119 4  Habitat variable codes given in Appendix 2.  48  Site  SSE  (N  BWI S_N  —i 1  B_B J  I 1•  I  I I  I  h-I I I  S_SW D  TN  I I  !Low  1 M_SE  -i  1 MNW  I I I I  T_S MNE  I I  1  2  3  4  5  Euclidean Distance  Fig. 5.  Cluster analysis of vesper sparrow abundances by study site for the Chilcotin study area, British Columbia, 1991/92. 49  Table 10. Mean habitat variables associated with low and high abundances of vesper sparrows in the Chilcotin study area, British Columbia, 1991/92. Vesper sparrow abundance Low (1.20—2.35)  Habitat van abl ea MAYVGCOV (%) MAYVGHT (cm) JUNVGCOV (%) JUNVGHT (cm) GRASS (%) ASPECT (°) FALLAUM  High (2.60—3.66)  21 6 32 11 40 113 146  32 8 41 12 33 208 548  a Habitat variable codes given in Appendix 2.  Long-billed Curlew The cluster analysis separated long—billed curlews into three groups associated with low, medium, and high breeding densities  (Fig.  6).  Trends in habitat associations identified by  cluster analysis (Table 11) were similar to those of the correlation analysis  (Table 7).  Highest curlew breeding  densities were on north—facing sites averaging 940 in elevation, with slope of  30  May/June vegetation height of 5—8 cm,  vegetation vertical cover of 14—22%, grass cover of 41%, and shrub cover of 0.3%.  Curlew densities were also highest on sites  with no summer or fall grazing, and with spring grazing levels averaging 420 AUM5.  50  Site  MNW TN  MNEJH_ Medium  D  I  I  MSE’’__ SSE -  I I  ILow  I  I  BW B_E C  2  6  4  8  .10  Euclidean Distance  Fig. 6.  Cluster analysis of long—billed curlew breeding densities by study site for the Chilcotin study area, British Columbia, 1991/92. 51  Table 11. Mean habitat variables associated with low, medium, and high breeding densities of long-billed curlews in the Chilcotin study area, British Columbia, 1991/92. Long-billed curlew breeding density Habitat variablea MAYVGCOV (%) MAYVGHT (cm) JUNVGCOV (%) JUNVGHT (cm) GRASS (%) SHRUBS (%) ELEV (m) ASPECT (°) SLOPE (°) SPRNGAUM SMMERAUM FALLàUM  Low (0—2)  Medium (3—5)  High (7)  35 9 46 13 42 0.06 953 192 5 410 265 496  21 7 32 11 33 0.5 842 158 7 569 175 223  14 5 22 8 41 0.3 940 8 3 420 0 0  a Habitat variable codes given in Appendix 2.  Western Meadowlark The cluster analysis separated western meadowlarks into three groups associated with low, medium, and high abundances (Fig. 7). analysis  Trends in habitat associations identified by cluster (Table 12) were somewhat similar to those of the  correlation analysis (Table 7).  Highest meadowlark numbers were  on south—facing sites averaging 585 m elevation, with slope of 17°, May/June vegetation height of 8-15 cm, vegetation vertical cover of 26—43%, and shrub cover of 2%.  Meadowlarks were also  most abundant on sites with fall grazing levels averaging 75 AUMs.  52  Site  edium_ SSE  I I I  MSEI  I B_W  i c’H S_N  Low 1  T_N  s_sw  I  B_E  I I I  M_NEI  I MNWI  —  I I I I I I I I  I  1  2  3  4  .5  Euclidean Distance  Fig. 7.  Cluster analysis of western meadowlark abundances by study site for the Chilcotin study area, British  Columbia, 1991/92. 53  Table 12. Mean habitat variables associated with low, medium, and high abundances of western meadowlarks in the Chilcotin study area, British Columbia, 1991/92. Western meadowlark abundances  Habitat variablea MAYVGCOV (%) MAYVGHT (cm) JUNVGCOV (%) JUNVGHT (cm) SHRUBS (%) ELEV (in) ASPECT SLOPE FALLAUM (0)  (0)  Low (0. 02—0. 45)  Medium (0.84—1.40)  22 6 31 10 0.14 929 142 4 331  45 12 57 16 0.03 919 200 8 463  High (2.35). 26 8 43 15 2 585 195 17 75  a Habitat variable codes given in Appendix 2.  Upland Sandpiper Upland sandpipers were found on sites with mean grass cover of 59%, bare ground cover of 13%,  litter cover of 24%, and tree  cover of 0.04%.  Sprague’s Pipit Sprague’s pipits were recorded on sites with mean .aspect of 24°, grass cover of 62%, bare ground cover of 27%, and litter cover of 12%.  4.3.5 Habitat Management Guidelines The range of variables associated with highest species diversity and greatest nunthers of individual species was narrower 54  than that measured throughout the entire study area (Table 13). The range of variables associated with high species diversity and species abundances was: 14—44% vegetation vertical cover (May and June combined), 5-15 cm vegetation height (May and June combined), 13—31% bare ground cover, 29—59% grass cover,  17-24%  litter cover, 0.10—2.0% shrub cover, 0.04% tree cover, 8—208° aspect, 585—940 in elevation, 3-17° slope, 0—420 spring AUMs, 0 summer AUMS, and 0—548 fall AUMs.  4.3.6 Habitat Structure Use by Birds  Mountain bluebirds were most commonly observed using habitat structures (71% of all bluebird observations), followed by western meadowlarks (50%), vesper sparrows (28%), and horned larks (18%).  These species did not have similar distributions  among habitat structures  (  <  0 • 001; Appendix 4).  Horned larks  used rocks and roads more than any other species (Fig. 8). Vesper sparrows used shrubs, western meadowlarks used trees, and mountain bluebirds used fences more than any other species. There were also differences between the availability of habitat structures and their use by each species species; Appendix 5).  (  <  0.001 for each  Horned larks used rocks and roads in much  greater proportions than were available.  Vesper sparrows used  trees, fences, and roads, while western meadowlarks used trees in greater proportions than were available.  Mountain bluebirds used  trees and fences in much greater proportions than were available. 55  Table 13.  Mean habitat variables associated with highest bird species diversity and species abundances in the Chilcotin study area, British Columbia, 1991/92. Study sites  H HOLA  VESP  LBCU  WEME  UPSA  SPPI  13  31  59  49  24  17  Habitat variablesa  (%)  26  36  21  32  14  26  7 (3—21) JUNVGCOV (%) 36 (13—75) JUNVGHT (cm) 11 (5—38) BAREGRND (%) 44 (9—58) GRASS (%) 37 (22—63) LITTER (%) 9 (5—39) 0.3 SHRUBS (%) (0—2) TREES (%) 0.001 (0—0.04) ASPECT (°) 155 (8—348) 892 ELEV (m) (585—1000) SLOPE (°) 6 (1—21) 595 SPRNGAUM (0—2050) 261 SMMERAUM (0—1367) FALLAUM 372 (0—2050)  9  6  8  5  8  44  30  41  22  43  13  10  12  8  15  MAYVGCOV  MAYVGHT(cm)  66 _ 7 ( )b  33  29  41  0.3  0.1  2.0 0.04  192  8  195  939  940  585  4  3  17  119  208  420  0  0 548  0  75  a Habitat variable codes given in Appendix 2. b  Range in variable measured across the 13 study sites.  56  79  70 60 50 40 .‘o o’  30 20 MOBL WEME EJVESP HOLA S Availability 0 S 0  S 0  S S S0 0 S Structure  Fig. 8.  Habitat structural availability and use by horned larks, vesper sparrows, western meadowlarks, and mountain bluebirds in the Chilcotjn study area, British Columbia, 1991/92. 57  5. Discussion 5.1 Bird Censuses Bird census results were typical for grassland habitats. Grassland bird communities are characteristically relatively simple.  Both intra— and inter—continental surveys have shown  that in general, grasslands provide habitat for two to six passerine species, and occasionally, as many nonpasserine species (Cody 1966, Wiens 1973b, Wiens 1974a, 1974b, Wiens and Dyer 1975, Cody 1985).  In this study, two passerine species were very  common (horned lark and vesper sparrow), while seven passerine species were relatively common (tree swallow, American crow, mountain bluebird, European starling, savannah sparrow, western meadowlark, and Brewer’s blackbird).  One nonpasserine species  the long—billed curlew, was also common. Within grassland bird communities, one or two widespread species tend to dominate (Graul 1980).  Wiens and Dyer (1975)  found that throughout North American grasslands, almost 50% of the birds recorded were of one species, while the two most abundant species comprised 75-88% of all observations.  In this  study, two species also dominated the bird community, but to a lesser extent than that found by Wiens and Dyer (1975).  Horned  larks and vesper sparrows, the dominant species in this study, comprised almost 34% and 26% of all observations, respectively, or almost 60% of all observations in total.  Differences in  proportions of the dominant bird species in this and Wiens and Dyer’s (1975)  study may be due to differences in bird censusing 58  —  Wiens and Dyer (1975) used spot-mapping or territory  techniques.  mapping techniques, whereas point—count censuses were used in In a comparison of spot-mapping and point-count  this study.  census techniques, Hooper and Savard (1991)  found that more  species, but fewer numbers of birds were detected with point— counts than with spot-mapping. Additional attributes of the bird communities in this study that were typical for grassland habitats included bird densities and species diversity.  Throughout North American grasslands,  bird densities typically average 0.5-2.0 pairs/ha (Wiens 1973b, Cody 1985)  and species diversity indices range from 0.44 to 1.43  (Wiens 1973b,  l974a, 1974b).  In this study, densities ranged  from 1.1 to 1.7 pairs/ha and species diversity indices ranged from 0.71 to 1.38. Characterization of the breeding bird communities in the study area also included records of the first occurrence and breeding of Sprague’s pipit, and the first breeding of upland sandpipers in British Columbia (McConnell Driessche  .  aj,. 1994, Van den  More recently, Roberts (1994)  in press).  recorded first occurrences for the Chilcotin grasslands of another three bird species  —  the American golden plover  (Pluvialis dominica), yellow-breasted chat (Icteria virens), and lark sparrow (Chondestes arammacus).  This suggests that the bird  communities of the Chilcotin grasslands may be more diverse than previously thought.  These communities, therefore, should  continue to be studied and monitored. 59  5.2 Long—billed Curlew Censuses  Breeding densities of curlews from 1990-1992 were fairly constant, but were higher on McDonald’s Ranch and the Toosey Indian Reserve in 1992 than in the previous two years.  This  suggests that either curlew numbers throughout the study area increased slightly in 1992, or that some curlews changed breeding sites between years.  More detailed and long—term breeding  density censuses throughout the study area are needed to clarify these trends. Most curlew breeding densities in this study were within the range found in other North American studies.  Densities in this  study were one pair/29—833 ha: those in other studies were one pair/12—40 ha in Idaho (Jenni et j. 1982), one pair/24 ha at Skookumchuck Prairie, British Columbia (Ohanjanian 1985), one pari/66—136 ha in Washington (Allen 1980), and one pair/600—700 ha in Saskatchewan (Sadler and Maher 1976). The relative stability in curlew numbers and breeding densities from 1990-1992 suggests that inconsistencies in survey methods, rather than a population decline, may have been responsible for the decrease in curlew breeding densities between this study and Ohanjanian’s (1987).  Ohanjanian (1987) did not  indicate when, or how many surveys she did.  If the 1987 surveys  were done during the pre-laying period in early April, counts of single males may have overestimated the number of breeding pairs, since not all males attract a female (Ohanjanian 1985, 1987). Similarly, if counts of males were made during the brood—rearing 60  period (mid-June through July), breeding pair nuibers may also have been overestimated since single males will fly more than half a kilometre to help with cooperative mobbing of predators (Redmond  .  1981, Ohanjanian 1987).  5.3 General Bird/habitat Associations Vegetation structure is considered to be th most important factor affecting grassland bird distribution (Tester and Marshall 1961, Hilden 1965, Wiens 1969, Whittaker and Woodwell 1972, Cody 1985).  In this study, the principal component analysis indicated  that vegetation structure accounted for most of the variability in the habitat characteristics.  The multiple correlations  indicated however, that topographic features and arthropod biomasses were more often associated with birds than was vegetation structure. The associations between birds and topographic features may have been partially due to correlations between topography and vegetation structure.  For example, multiple correlations showed  that in general, vegetation patchiness, shrub cover and bare ground cover decreased, and grass, litter, and tree cover increased as elevation increased (Appendix 6).  Steeper slopes  were correlated with taller, denser, patchier vegetation, more bare ground and shrub cover and less grass and litter cover than gently sloping sites.  South— and west—facing sites were  associated with taller, denser, patchier vegetation, less bare ground and grass cover, and more shrub and tree cover than north— 61  and east-facing sites (Appendix 6). Despite these associations, topographic features explained The  only 9-12% of the variability in vegetation structure.  associations of birds with topographic features then, remains somewhat unclear.  No other studies were found in which grassland  topography was characterized and correlated with bird communities.  It may be that birds cue—in on microsites  associated with different topographic features.  For example,  microsite characteristics such as rate of spring snow melt, amount of radiant light, air temperature intensity and fluctuation, and evapotranspiration rates could affect the quality of nesting sites and the reproductive success of breeding birds.  More research is needed to clarify the associations  between grassland birds and topography. Although arthropod biomasses in this study were associated with birds more than was vegetation structure, many of the bird/arthropod correlations (25 of 48) were negative.  Although  cause and effect can not be concluded from correlation analysis, it is unlikely that grassland birds were so selective in their food preferences that certain species avoided using sites due to the presence of certain arthropod types.  If the negative  correlations were excluded, then vegetation structure would be more often associated with birds than were arthropod biomasses. Other studies have concluded that guild structures of grassland birds were more likely associated with habitat structure than with food supply (Folse 1981). 62  The general lack of positive associations between bird species and total arthropod biomass suggests that strong habitat selection pressure based on overall food resourcs, did not occur among the birds in this study.  Although food resources for  breeding grassland birds may, at times, be extremely important, they are probably not a consistent limiting factor on an annual basis (Wiens 1974a).  Because primary productivity in grasslands  occurs within a short season, and because breeding grassland birds have low energy demands, it is likely that food resources are often superabundant (Wiens 1974a, 1977, Wiens and Rotenberry 1979).  Short—term studies like this one, however, could miss any  years when food may be limiting (Newton 1980).  The diets of  grassland birds can be highly variable between individuals, sites, and years (Wiens and Rotenberry 1979).  This too, suggests  that food resources are rarely limiting, and that individuals and populations exploit food resources opportunistically (Wiens and Rotenberry 1979). If grassland birds are limited at all by food resources, it may be due more to temporal or spatial availability than to abundance of arthropods (Wiens l974a).  The method used for  collecting arthropods in this study may also have contributed to the lack of clearly defined relationships between grassland birds and food resources.  For example, widely—dispersed arthropods may  not be adequately sampled with small pan traps, while other arthropods may be more easily caught by traps than by foraging birds (Wiens 1977). 63  The components of vegetation structure most often associated with grassland birds include grass height and density (Cody 1966, Creighton 1974, Ohanjanian 1985), litter and vegetation patchiness (Wiens 1969,  1973b, l974a, l974b, 1976, Wiens and Dyer  1975), and amount of ground and shrub cover (Bock  i. 1984).  Similar results were obtained in this study, but associations between birds and grass and tree cover were also identified. Wiens and Rotenberry (1981) suggested that complete understanding of bird/habitat relationships requires knowledge of vegetation floristics as well as structure  —  in some cases,  floristic data may contribute more to the ability to predict bird/habitat associations than does structural data. Unfortunately, the methods of floristic sampling used in this study, although consistent with those of the Ministry of Forests, did not provide data that produced easily interpreted or meaningful correlation analyses with the bird data.  More precise  measurements than the mid—points of the six cover classes may have provided more useful data, especially for the more uncommon plant species.  It should be noted though, that Wiens and  Rotenberry’s (1981) conclusions about the association of birds and vegetation floristics were based on studies of shrub—steppe bird communities.  In these habitats, bird species were  correlated with different shrub species, which clearly, have strong structural characteristics.  Cody (1968) concluded from  inter—continental studies of grasslands (i.e., non—shrub—steppe habitats) that although some bird species have specialized food 64  and habitat requirements, it is unlikely that most species recognize and exploit differences between species within a plant genus.  Consequently, because only one site in this study had  some characteristics of a shrub—steppe habitat, the characterization of the floristic component of bird habitats was probably not as important as that of the vegetation structural component. Of all the habitat characteristics, livestock grazing had the fewest associations with birds.  Correlations between birds  and grazing may have been due to the effects of brazing on vegetation structure (Wiens 1973b, Wiens and Dyer 1975).  In  general, cover of bare ground increased, but grass, litter, shrub, and tree cover, and vegetation height, cover, and patchiness decreased as AUMS increased (Appendix 7).  The amount  of variability in vegetation structure attributed to grazing however, was only 5-7% (Appendix 7).  This suggests that if birds  did respond to grazing levels, it may have been due to factors other than, or in addition to changes in vegetation structure. It is difficult to assess, however, to which factors birds may have responded.  For example, birds could have been affected by  trampling and disturbance due to grazers.  Significant nest  losses can occur at stocking densities greater than 2.5 AU/ha (Jensen  1990), and species such as the long-billed curlew  can experience serious nest losses and abandonments due to livestock trampling and harassment (Sugden 1933, Jenni 1982, Redmond and Jenni 1986).  The behavioural responses of 65  grassland birds to grazers however, were not investigated in this study. The impacts of grazing on birds can also be confounded by differences in climatic patterns, soil characteristics, and vegetation floristics and phenology between study sites. Additionally, the use of AUMs, although consistent with the Ministry of Forests methods, may not have adequately assessed grazing intensity.  Experiments on livestock trampling of  simulated ground nests have shown that more meaningful assessments of trampling damage are made when numbers of animals per hectare, rather than livestock weights and forage demands, were used as measures of grazing intensity (Jensen  j,. 1990).  Comparison of vegetation phenology between study sites at time of grazing, and calculations of AUMS on a per unit area basis may then, have given a more meaningful assessment of grazing influences throughout the study area.  Conclusions on the impacts  of grazing on grassland birds in this study then, should be cautious, especially since the effects of soil, site conditions, and precipitation regimes may be more important than grazing in affecting food, cover, and water for grassland birds (Ryder 1980).  5.4 Specific Bird/habitat Associations 5.4.1 Species Diversity The habitat variables measured in this study, explained much of the variability (85%)  in bird species diversity throughout the 66  study area.  Bird diversity is often positively correlated with  vegetation complexity (Roth 1977, Wiens and Rotenberry 1981, Cody 1985).  Similar results were found in this study, as diversity  was greatest on sites with the tallest, densest vegetation.  The  negative correlation between diversity and grass cover also suggests that diversity was greater on sites with more complex vegetation structure than where grasses dominated.  Diversity may  have been positively correlated with aspect since south—facing sites had greater vegetation height and vertical cover and less grass cover than east—facing sites.  Species diversity was also  negatively correlated with spring grazing, possibly because grazing reduced vegetation height and cover during the nesting season.  Species richness, a component of species diversity,  generally declines as grazing pressure increases (Owens and Myres 1973, Wiens l973b, Wiens and Dyer 1975, Kantrud 1981).  5.4.2 Horned Lark  Horned larks typically nest in bare, sandy, or stony ground with sparse grass cover (Harrison 1984); consequently, most studies on horned larks found negative associations with tall, dense vegetation, and forb and shrub cover, and positive associations with bare ground (Wiens l973b, Bock and Webb 1984, Wiens and Rotenberry 1985, Larson and Bock 1986). results were found in this study.  Similar  Horned larks were least  abundant on sites with tall, dense vegetation, shrub cover, and patchy vegetation height.  Larks may also have been least common 67  on steep, south—facing sites because vegetation cover and height, and shrub cover increased with slope and aspect.  Positive  associations between larks and elevation may have been due to reduced shrub cover at higher elevations. Horned larks’ affinity for short, open vegetation may be due, in part, to this species’ means of foraging.  Larks are  rapid feeders which pursue, rather than search for prey (Cody 1968).  Pursuing behaviour is often most efficient in  homogeneous, short—statured grasslands (Cody 1968).  Horned  larks’ inability to forage effectively in tall grass can result in chicks starving to death in the nest (Cody 1985). The diets of horned larks tend to be highly variable, seasonally and geographically, and in composition (Wiens and Rotenberry 1979, Rotenberry 1980).  Although horned larks are  omnivorous, during the breeding season, seeds can comprise up to 73% of the diet (Wiens and Rotenberry 1979).  This then, may  explain the lack of positive associations between horned larks and arthropods in this study. Although no association of horned larks with livestock grazing was found in this study, horned larks generally, are more common in more heavily than lightly grazed areas, presumably due to this species’ association with low, open vegetation, and bare ground (Maher 1973, Owens and Myres 1973, Wiens l973b, Karasiuk .  1977, Ryder 1980, Kantrud 1981, Kantrud and Kologiski  1983, Bock  j,. 1984, Renken and Dinsmore 1987).  Observations of habitat structural use revealed the 68  importance of rocks and roads to horned larks.  Rocks were used  more than other structures for singing or perching posts. Although this study did not find correlations between horned larks and bare ground, larks did use dirt roads for feeding and dust-bathing sites.  The importance of roadways to this species  was also noted at a site in Newfoundland, where horned lark territories were linearly distributed along a road that males used for dust-bathing, roosting, and singing (Cannings and Threfall 1981).  In this study, large numbers of horned larks  were also seen using dirt roads as evening roost sites.  Horned  larks are known to dig roost sites, often behind protective vegetation, to reduce radiative and convective heat losses at night (Trost 1972).  5.4.3 vesper Sparrow Vesper sparrows were most common on sites with tall, dense vegetation and low grass cover.  Sparrow numbers were also  greater on south— than east—facing sites, possibly because of taller, denser vegetation and less grass cover in those areas. The negative correlation between sparrows and grass cover in this study, suggests that sparrow abundance may have been greater on sites with more complex vegetation structure than where grasses dominated.  Other studies have found that vesper sparrows were  positively correlated with vegetation density, ahd litter and ground cover, but negatively correlated with cover of bare ground around nest sites (Wray and Whitmore 1979, Reed 1986). 69  Given the habitat associations for this species, vesper sparrows might be expected to be most common in ungrazed or lightly grazed grasslands.  In some studies this was true (Maher  1973, Kantrud and Kologiski 1983), in others, it was not (Owens Vesper sparrows use a range of  and Myres 1973, Kantrud 1981).  habitat types including grasslands, shrub-steppes, and grassland/shrub-steppe ecotones (Johnsgard 1979, Kantrud and Vesper sparrows also nest on or  Kologiski 1983, McNicholl 1988).  above the ground, and frequently defend territories as large as 0.8 ha (Johnsgard 1979, Kantrud and Kologiski 1983).  These  rather broad habitat associations could explain any differences in habitat descriptions and grazing results between studies. is difficult then, to determine what, if any, grazing has on vesper sparrows.  It  impacts livestock  In this study, the positive  correlations of sparrows with grazing is unclear, but could be a result of reduced grass cover in spring due to fall grazing. The data on habitat structure use indicated that vesper sparrows used shrubs for perching and displaying, more than any other species.  Similarly, Hooper and Savard (1991)  found  positive correlations between vesper sparrows and shrub cover. Vesper sparrows also used trees and fences in greater proportions than were available.  Vesper sparrows may be associated with  shrubs, trees, and fences, because of their use of elevated singing perches for territorial defense (Johnsgard 1979, Terres 1980).  Unlike horned larks, which sing from the ground or in  flight, vesper sparrows sing primarily from elevated perches 70  (Castrale 1983).  In the Okanagan Region of B.C., vesper sparrows  have also been found using shrubs (i.e., sagebrush bushes) for nesting cover (Cannings et al. 1987).  In such areas, livestock  grazing may have benefitted vesper sparrows by increasing the amount of available sagebrush cover (Cannings  i. 1987).  5.4.4 Long-billed Curlew More habitat associations were found using curlew breeding densities than curlew numbers from point—counts, and those associations explained much greater variability in curlew densities (96%) than in curlew numbers (38%).  This suggests that  studies which use breeding territory censuses may identify more detailed bird/habitat associations than were generally found in this study. Long—billed curlews were most common in short, open, grassy vegetation with low shrub cover.  Curlews were also most common  on gently sloping, high elevation sites with low aspects.  These  associations with topography may be due to low vegetation height and vertical cover, low shrub cover, and high horizontal cover of grass on those sites.  Long-billed curlews typiclly nest in  short, open grasslands, and may require these sites for communal predator detection, effective communication between nesting birds, and ease of movement of chicks when feeding (McCallum .  1977, Allen 1980, Renaud 1980, Bicak  .  1982, Ohanjanian 1986, 1987).  1982, Jenni  Curlews may also require  patchy grass cover for camouflage and thermal cover for chicks 71  (Allen 1980, Pampush 1980). The negative associations between curlews and grazing in this study were somewhat confusing, since grazing generally reduces vegetation height and density.  Grazing studies have  consistently found that curlews are more abundant in heavier— 1982,  than lighter-grazed grasslands (King 1978, Bicak  If curlews in this  Kantrud and Kologiski 1982, Ohanjanian 1987). study were responding negatively to grazing, disturbance effects from grazing animals.  it may be due to  In southwestern Idaho,  10% of long-billed curlew egg clutches were abandoned when nesting birds were harassed by grazing livestock (Jenni g 1982).  Curlew nest abandonments have been shown, to be influenced  by stocking rates, duration and frequency of grazing, and timing of grazing during the incubation period (Jenni  .  1982).  Greater insight into the potential influence of livestock grazing on long-billed curlews in the Chilcotin grasslands may be gained from more research on the behavioural responses of curlews to grazing animals, and on the reproductive success of curlews on sites with different grazing regimes.  5.4.5 Western Meadowlark In this study, western meadowlarks were commonly associated with shrub cover, and tall, dense, patchy vegetation cover.  An  increase in meadowlark numbers with slope and aspect may have been due to greater shrub cover and vegetation height, cover, and patchiness, on steeper, south—facing sites. 72  Meadowlarks may also  have been more common at lower elevations due to greater shrub cover and vegetation patchiness on those sites.  Observations of  habitat structural use indicated that trees, which were used for perching and displaying, were also important habitat components for meadowlarks. Nests  Western meadowlarks build their nests in tall grass.  are usually well hidden in grass clumps, and consist of a scraped bowl covered with a domed canopy of grasses and forbs (Johnsgard 1979, Harrison 1984).  Meadowlarks also use elevated singing  posts (Terres 1980, Cannnings  This use of tall  j,. 1987).  grass for nesting, and elevated structures for singing posts may explain why meadowlarks in this study were associated with tall dense vegetation, shrub cover, and trees.  The general lack of  association of meadowlarks with arthropods in this study, may be a result of the broad composition and geographically variable diets typical of western meadowlarks (Wiens and Rotenberry 1979). Although other studies have found positive correlations between western meadowlarks and shrub cover and vegetation vertical structure (Wiens and Rotenberry 1981), meadowlarks are considered habitat generalists that occupy a range of habitats from tall—grass prairies, wet meadows, hayfields, and weedy borders of croplands to short—grass and sage prairies (Johnsgard 1979, Rotenberry and Wiens 1981, Larson and Bock 1986).  Because  western meadowlarks tend to be habitat generalists then, grazing studies have shown that meadowlarks are associated both with grazed and ungrazed grasslands (Johnson 1972, 73  1973,  1974, Owens  and Myres 1973, Hopkins 1980, Kantrud 1981, Kantrud and Kologiski 1983, Renken and Dinsmore 1987).  In this study, western  meadowlarks generally decreased with increased fall grazing levels, possibly because fall grazing resulted in reduced spring vegetation height, cover, and patchiness on breeding sites.  5.4.6 Brewer’s Blackbird  Brewer’s blackbirds nest in a variety of habitats, but are most often associated with shrubs and trees near moist meadows and fields, which are used as feeding sites (Harrison 1984, Cannings  1987).  This may explain why blackbirds in this  study were most strongly associated with shrub cover.  Brewer’s  blackbirds were also most common on steeply sloping, low— elevation sites, possibly due to greater shrub cover on those sites.  The variability in nesting habitats of Brewer’s  blackbirds may explain why habitat associations for this species were otherwise, not well defined in this study.  5.4.7 Tree Swallow Although tree swallows are found in a variety of habitats in the Okanagan Region of B.C., they are most common around lakes and ponds that have open spaces for insect hunting, and structures with nest holes unobstructed by vegetation (Cannings 1987).  In this study, tree swallow numbers increased with  tree cover, presumably because of the potential nest sites afforded by trees.  The variability in nesting habitats of tree 74  swallows however, and the fact that point—counts were generally located away from water bodies, may explain why habitat associations for tree swallows were generally not well defined in this study.  5.4.8 Mountain Bluebird  Mountain bluebirds were most common on gently sloping, high— elevation sites with trees.  Observations of habitat structural  use indicated that fences were also important habitat features for bluebirds.  Although mountain bluebirds are associated with  open grasslands, scrublands, and treeless meadows, they require cavities in which to nest (Cannings  1987).  This explains  the association between bluebirds and trees in this study.  It  also explains the use of fences by bluebirds, since bluebird nest boxes have commonly been placed on fences by local ranchers and the Williams Lake Naturalists.  5.4.9 Savannah Sparrow Savannah sparrows numbers increased with amount of bare ground, and declined as grass cover increased.  These results  contradicted other studies of savannah sparrow habitat associations.  Savannah sparrow breeding territories are  characterized by vertically dense vegetation, grass cover, forb density and cover, and litter depth and patchiness (Wiens 1973a). Nests are usually built in dense ground cover where they are well-concealed by overhanging vegetation (Linsdale 1938, Tester 75  and Marshall 1961, Lein 1968, Wiens 1969, Potter 1972, Terres 1980). Savannah sparrows also tend to occupy wet meadow zones of mid— and tall—grass prairies (Johnsgard 1979).  General  observations suggested that savannah sparrows in this study were also most common in wet areas.  Because point—counts were  generally located away from large wet areas, it is more likely that savannah sparrow habitat associations were not adequately assessed in this study, rather than that sparrows had different habitat requirements in the study area. Savannah sparrows are most common in areas with little or no livestock grazing (Lincoln 1925, Rand 1948, Maher 1973, Owens and Myres 1973, Karasiuk  .  1978, Maher 1979,  1977, Page  Kantrud 1981, Kantrud and Kologiski 1983).  In this study,  savannah sparrows were positively associated with spring and fall grazing levels.  Again, the contradictions between this and other  studies may be because savannah sparrow habitat associations were not adequately assessed in this study.  5.4.10 Upland Sandpiper In B.C., upland sandpipers have been recorded using open, grasslands, overgrown fallow fields, bogs, burns, wet pastures, golf courses, .  1990).  lawns, meadows, dirt roads, and mudflats (Campbell No details on nesting habitat in B.C. were  available, however, before this study.  The nest site in this  study was a grassy alcove surrounded on three siçles by trees and 76  shrubs.  Grasses comprised 75—95%, while  bare soil comprised  only 5—25% of the horizontal ground cover (Van den Driessche j., in press).  This would explain why upland sandpipers in this  study were negatively associated with bare ground, and positively associated with grass and tree cover.  Conclusions about upland  sandpiper habitat requirements should be cautious though, because numbers of breeding sandpipers in the study area were so low (e.g.,  12 observations representing an estimated two breeding  pairs). Other studies have recorded the upland sandpiper’s association with mixed-grass and tall-grass habitats (Wiens 1973b, Rotenberry and Wiens 1980); consequently, this species tends to be most common in ungrazed to moderately grazed areas (Kantrud 1981, McNicholl 1988).  No associations of sandpipers  with grazing were found in this study, possibly due to the low numbers of this species within the study area. Arthropods accounted for more variability in upland sandpiper numbers than any other species.  Sandpipers also had  more positive correlations with different arthropod types than any other species.  This suggests that food resources may be  important factors in habitat selection for upland sandpipers in the study area.  Given the rather vague results of relationships  between the other bird species and food resources in this study, however, conclusions on the importance of arthropods to upland sandpiper habitat selection within the study area, should not be made without more detailed studies on upland sandpiper feeding 77  ecology.  5.4.11. Sprague’s Pipit Sprague’s pipits tend to be associated with extensive areas of grasslands dominated by grasses of medium height (Johnsgard 1979).  Pipits nest on the ground, in growing herbage, and nests  are well—concealed by overhanging vegetation (Harrison 1984). Similar nesting characteristics were found in this study (McConnell et al. 1994), and explain why pipits were positively associated with grass and litter cover, and negatively correlated with cover of bare ground.  Conclusions about Sprague’s pipit  habitat requirements based on this study should be cautious however, since pipit numbers were so low (e.g.,  16 observations  representing one breeding pair). Given this species’ association with tall grass habitats, Sprague’s pipits are generally most common in ungrazed to moderately areas (Maher 1973, Owens and Myres 1973, Kantrud and Kologiski 1983).  The lack of association between pipits and  grazing in this study may have been due to the low numbers of pipits recorded.  5.4.12 Brewer’s Sparrow Brewer’s sparrows are characteristic of sagebrush grasslands in British Columbia (Cannings  j,.  1987).  This may explain why  Brewer’s sparrows in this study, were most common on steeply sloping sites with patchy vegetation, and high shrub and tree 78  cover.  More detailed habitat associations for Brewer’s sparrows  may have been obtained if more sagebrush sites had been censused. These sites were under—represented in this study because they were often inaccessible by vehicle, and/or too small to accommodate a sufficient number of point—counts.  The  distribution of Brewer’s sparrow throughout the Chilcotin remains unclear however, as the species was not recorded in the area until 1992  (A. Roberts, pers. comm., Roberts 1994).  More surveys  are needed then, to characterize Brewer’s sparrow habitat associations throughout the study area.  5.4.13 Sharp—tailed Grouse  Sharp-tailed grouse occupy a variety of habitats, but common features of these habitats include open grasslands adjacent to brushy or scattered open woodlands (Campbell g 1990).  In the Chilcotin, open parklands adjacent to spruce,  Douglas—fir, or trembling aspen stands are characteristic sharp— tailed grouse habitat (Campbell  .  1990).  Although some  point—counts were located near the grassland/woodland ecotone, habitat measurements were generally made in open grassland.  This  may explain why strong habitat associations were not found for sharp—tailed grouse in this study. Additionally, Moyles (1981)  found that sharp—tailed grouse  used different sites within the grassland/woodland border during different seasons and different times of the day. mornings of spring,  In the early  (i.e., when point—counts were conducted), 79  grouse feed in trees and shrubby borders, as well as in open grasslands (Moyles 1981); consequently, censuses of the open grasslands may have underestimated sharp—tailed numbers in the study area. Sharp-tailed grouse habitat requirements would probably best be determined then, by sampling habitat characteristics at known lekking, nesting, and feeding sites.  In the interim, maintenance  of a mosaic of open grasslands associated with extensive shrub/tree ecotones, may provide optimal habitat for sharp-tailed grouse in the study area (Moyles 1981).  5.4.14 Short-eared Owl  Short—eared owls were most comnmon in shrubby areas, and on steeply sloping sites at low elevations.  Because most  observations were of hunting birds, however, little information about habitat requirements for this species was obtained from this study.  Behavioural observations of habitat use, and  detailed habitat measurements around nest sites are needed to identify true habitat requirements for short-eared owls in the study area.  5.5 Habitat Structural Use by Birds  Observations of habitat structural use by birds identified habitat associations that were not revealed in the correlation analyses.  This illustrates the importance of including  behavioural observations in grassland bird habitat studies to 80  identify meaningful bird/habitat associations.  6. Conclusions This study successfully met the research objectives of characterizing grassland breeding bird communities of the study area, and of identifying associations between grassland habitat characteristics and breeding bird diversity and species abundances.  The research hypothesis that bird diversity and  species abundances were most often associated with vegetation structure was not fully supported by this study. often associated with topographic features.  Birds were most  This may have been  due to correlations between topography and vegetation structure, or it may have been due to microsite differences associated with topography.  Nevertheless, vegetation structure was considered to  be the second factor of greatest influence on bird communities in this study. As predicted, species diversity was greater in more structurally complex habitats, given that complexity was considered to be based primarily on vegetation height, vertical cover, and patchiness.  Also as predicted, some species were more  strongly associated with structurally complex habitats than were other species.  For example, horned larks and long—billed curlews  were characteristic of short, open grass habitats, whereas vesper sparrows and western meadowlarks were associated with tall, dense grass sites. The research hypothesis that breeding bird diversity and 81  species abundances were also associated with food resources was not supported in this study.  This may have been due to sampling  methods that did not adequately sample types and numbers, and/or time and spatial distributions of arthropods, or it may have been due to a general lack of close coupling between grassland birds and food resources. This study did not support the hypothesis that bird diversity and species abundances were affected by livestock grazing.  The prediction that grazing affected birds by altering  habitat structure was supported somewhat, since vegetation height, vertical cover, and patchiness declined with increased grazing pressure.  The amount of variability in structural  components accounted for by grazing however, was very low.  Bird  diversity declined with grazing, but species characteristic of short—grass habitats were not more abundant at higher grazing levels, nor were the tall—grass species consistently more abundant at lower grazing levels. The inability to define trends between grassland birds and livestock grazing may mean that AUM5 did not adequately assess the impacts of grazing intensity on birds, or that behavioural interactions between birds and livestock were occurring.  Due to  the problems with defining associations between birds and food resources, the prediction. that livestock grazing affected grassland birds by altering food resources, was not examined.  82  7. Management Recommendations This study has provided preliminary information on grassland bird communities of some of the Chilcotin grasslands, and through the identification of species habitat associations and the creation of species management guidelines, has provided some direction in managing grasslands to maintain avian diversity. Based on this study, grassland habitats in the study area should be managed as a mosaic of habitat types ranging from short, open vegetation to tall, dense vegetation.  Maintenance of rocks,  shrubs, trees, and grass/shrub and grass/tree ecotones within these mosaics is also important.  It may be possible to use  livestock grazing to create and/or maintain these habitat mosaics. It should be noted however, that the bird/habitat associations and management guidelines in this study are specific to the study area, and are not necessarily applicable to other areas or other time periods.  Management and maintenance of avian  diversity throughout the Chilcotin-Cariboo grasslands should therefore, be based on more detailed information than was provided in this study.  A greater understanding of grassland  bird communities throughout the region could be achieved by undertaking the following procedures: 1.  Monitoring of grasslands should be done throughout a wider area and longer time period than was covered in this study. From 1991—1993, five species of birds previously unknown in the Chilcotin grasslands were recorded (McConnell 83  1994, Roberts 1994, Van den Driessche et flj.,  in press).  This suggests that the bird communities of these grasslands may be more diverse than previously thought.  Future bird  inventories should be made initially for five consecutive years, and then repeated one year in a five—year interval. These inventories should be made throughout the Cariboo and Chilcotin grasslands.  Also, despite the recent work by  Roberts (1994), detailed information on birds of the low elevation (i.e., sagebrush) grasslands is lacking in this region.  These sites were too inaccessible to be properly  censused in this study; 2.  Future bird censuses should be done using spot—mapping rather than by point—count censuses.  Point—counts were used  in this study because they are more efficient and provide more representative sampling over larger areas than does spot-mapping (Verner 1985).  Spot-mapping, however, provides  better estimates of bird densities (Verner 1985).  Because  spot-mapping is based on plotting of breeding territories, it would be easier to identify and measure the habitat variables most strongly associated with those territories. This may provide more detailed and accurate habitat associations than were found in this study; 3.  The correlation analyses in this study identified bird/habitat associations only.  Cause and effect of bird  habitat use can not be identified by these analyses.  Future  research should incorporate behavioural observations of 84  habitat use with bird censuses.  As this study has shown,  behavioural observations can identify impor.tant habitat requirements that may be overlooked by simply measuring habitat features around locations of bird sightings.  By  recording habitats used for such activities as mating, nesting, feeding, and roosting, and by noting the availability of those habitats versus their use, details of species habitat selection can be determined; 4.  The reproductive success of individual bird species in different grassland habitats should also be studied, as this could further identify and clarify bird/habitat associations;  5.  Given the variability in grassland bird diets and food resources, it is questionable whether further studies on food resources would clarify bird/habitat associations in the Chilcotin grasslands.  If such studies are considered  necessary, information on diets of individual species, and on prey presence, abundance, and accessibility through time and space should be collected; and 6.  Although the correlation analyses in this study identified some associations between birds and livestock grazing, the cause for those relationships remains unclear.  The  potential impacts of livestock grazing on grasslands birds may be best determined through long-term replicated grazing trials.  Such trials would account for natural variability  in bird populations, and would make statistical inferences 85  possible.  Where replicated grazing trials are not feasible,  livestock numbers, season and duration of grazing, and plant phenology and standing crop biomass on the study sites should be recorded and correlated with vegetation structure. Differences in climatic patterns and site conditions between study areas should also be noted, as these can influence the effects of grazing on vegetation.  In this  study, AIJM5 were used to quantify grazing intensity, as this is the method used by the Ministry of Forests.  A more  appropriate measure of grazing intensity may be the number of livestock/ha.  In addition to these recommendations,  behavioural observations of disturbance effects of grazing livestock on birds should be made.  Experiments of livestock  trampling of artificial ground nests, and studies of the reproductive success of birds in grasslands with different grazing regimes would help clarify the potential impacts of livestock grazing on birds.  86  6 Literature Cited Allen, J.N. 1980. The ecology and behavior of the Long-billed Wildl. Monogr. 73:3-67. Curlew in southwestern Washington. American Ornithological Union. 1983. Check-list of North American birds. Sixth ed. Allen Press, Inc., Lawrence, Kansas. 877pp. 1984. Report of the meeting of the committee on classification and nomenclature. Auk 101:348. 1985. Thirty-fifth supplement to the American Ornithologist’s Union Check-list of North American birds. Auk 102:680-686. 1987. Thirty-sixth supplement to the American Ornithologist’s Union Check-list of North American birds. Auk 104:591—596. 1989. Thirty-seventh supplement to the American Ornithologist’s Union Check-list of North American birds. Auk 106:532—538. Baldwin, P.H. 1971. Diet of the mountain plover at the Pawnee National Grassland, 1970—71. U.S. IBP Grassland Biome Tech. Rep. No. 134. 22pp. jjj R.A. Ryder 1980. Effects of grazing Management of western on bird habitats. Pages 51-64 forests and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT-86, Ogden, Utah. 1973. The feeding regime of granivorous birds in shortgrass prairie in Colorado, U.S.A. Pages 237-248 jn S.C. Kendeigh and J. Pinowski, eds. Productivity, population dynamics and systematics of granivorous birds. Polish Scientific Publishers, Warsaw. 4lOpp. j R.A. Ryder 1980. Effects of grazing on bird habitats. Pages 51—64 j Management of western forests and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT—86, Ogden, Utah. Bicak, T,K., R.L. Redmond, and D.A. Jenni. 1982. Effects of grazing on Long-billed Curlew breeding behavior and ecology Wildlife-livestock in southwestern Idaho. Pages 74-85 relationships symposium: Proc. 10. J.M. Peek and P.D. Dalke, eds. Univ. Idaho For. Wildi. Range Exp. Stn., Moscow. Bock, C. E., J.H. Bock, W.R. Kennedy, and V.M. Hawthorne. 1984. Responses of birds, rodents, and vegetation to livestock exciosure in a semidesert grassland site. J. Range Manage. 37:239—242. and B. Webb. 1984. Birds as grazing indicator species in southeastern Arizona. J. Wildi. Manage. 48:1045-1049. 87  Breymeyer, A.I., and G.M. van Dyne. 1980. Grasslands, systems analysis, and man. Cambridge University Press, New York. 950pp. British Columbia Ministry of Environment. 1991. Managing wildlife to 2001: a discussion paper. B.C. Mm. Environ., Wildi. Branch, Victoria, B.C. 152pp. British Columbia Ministry of Environment, Lands,, and Parks. 1993. Red and Blue Lists. B.C. Mm. Environ. Lands, and Parks, Wildl. Branch, Victoria, B.C. Burt, W. H., and R.P. Grossenheider. 1976. A field guide to the mammals. Third ed. Houghton Mifflin, Boston. 289pp. Cameron, E.S. 1907. The birds of Custer and Dawson counties, Montana. Auk 24:241-270. Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M. Cooper, G.W. Kaiser, and M.C.E. McNall. 1990. The birds of British Columbia. Vol. 2. Royal British Columbia Museum, Can. Wildi. Serv. 514pp. Cannings, R.A., R.J. Cannings, and S.G. Cannings. 1987. Birds of the Okanagan Valley, British Columbia. Royal British Columbia Mus., Victoria, B.C. 420pp. Cannings, R.J. 1981. Notes on the nesting of Horned Larks on the Chilcotin Plateau of British Columbia. Murrelet 62:21-23. and w. Threfall. 1981. Horned Lark breeding biology at Cape St. Mary’s, Newfoundland. Wilson Bull. 93:519—530. Castrale, J.S. 1983. Selection of song perches by sagebrush— grassland birds. Wilson Bull. 95:67—655. Cody, M.L. 1966. The consistency of intra- and inter-continental grassland bird species counts. Am. Nat. 100:371—376. 1968. On the method of resource division in grassland bird communities. Amer. Nat. 102:107—147. 1985. Habitat selection and open—country birds. Pages 191-226 j Habitat selection in birds. M.L. Cody, ed. Academic Press.  88  Creighton, P.D. 1974. Habitat exploitation by an avian groundforaging guild. Ph.D. Thesis, Colorado State Univ., Ft. Collins. 139pp. j R.A. Ryder. 1980. Effects of grazing on bird habitats. Pages 51-64 Management of western forests and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT-86, Ogden, Utah. Daubenmire, R. New York.  1978. Plant geography. Academic Press. New York, 338pp.  Demarchi, D.A. 1988. A regional wildlife ecosystem classification system for British Columbia. Pages 11—19 j H.A. Stelfox and G.R. Ironside, compilers. Land/Wildlife integration workshop No. 3, Mount Ste.—Marie, Quebec, 16-19 September 1985. Ecological Land Classification Series No. 22. Can. Wildl. Serv., Ottawa, Ont. Douglas, G.W., G.B. Straley, and D. Meidinger. 1989. The vascular plants of British Columbia. Part 1: Gymnosperms and dicotyledons (Aceraceae through Cucurbitaceae). Special Rep. Series 1. B.C. Mm. Forests, Victoria, B.C. 208pp. 1990. The vascular and plants of British Columbia. Part 2: Dicotyledons (Diapensiaceae through Portulaceae). Special Rep. Series 2. B.C. Mm. Forests, Victoria, B.C. 158pp. 1991. The vascular and plants of British Columbia. Part 3: Dicotyledons (Primulaceae through Zygophyllaceae and Pteridophytes). Special Rep. Series 3. B.C. Mm. Forests, Victoria, B.C. 177pp. Folse, L.J., Jr. 1981. Ecological relationships of grassland birds to habitat and food supply in East Africa. Pages 160166 in The use of iuultivariate statistics in studies of wildlife habitat. D.E. Capen, ed. USDA For. Serv. Gen. Tech. Rep. RN-87. Graul, W.D. 1980. Grassland management and bird communities. Pages 38—47 jfl Management of western forests and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT—86, Ogden, Utah. Harrison, C. 1984. A field guide to nests, eggs, and nestlings of North American birds. Second ed. Collins, Toronto. 416pp. Hewitt, G., E.W. Huddleston, R.J. Lavigne, D.N. Ueckert, and J.G. Watts. 1974. Rangeland entomology. Soc. Range Mgmt. Range Sci. Ser. No. 2. 127pp.  89  Hilden, 0. 1965. Habitat selection in birds. Ann.. Zool. Fenn. 2:53—75. jj J.A. Wiens. 1973. Pattern and process in grassland bird communities. Ecol. Monogr. 43:237-270. Hooper, T.D., and M.D. Pitt. 1994. Problem analysis for Chilcotin-Cariboo grassland biodiversity. B.C. Mm. Environ., Lands and Parks, Wildl. Branch, Williams Lake, B.C., 2lOpp. Hooper, T.D., and J.-P. Savard. 1991. Bird diversity, density, and habitat selection in the Cariboo—Chilcotin grasslands: with emphasis on the Long-billed Curlew. Technical Report Series No. 142. Canadian Wildlife Service, Pacific and Yukon Region, British Columbia. lO2pp. Hope, G.D., W.R. Mitchell, D.A. Lloyd, W.R. Erickson, W.L. Harper, and B.M. Wikeem. 1991. Interior Douglas-fir Zone. 3 D. Meidinger and J. Pojar, compilers and Pages 153-166 j eds. Ecosystems of British Columbia. B.C. Mm. For. Spec. Rep. Ser. 6, Victoria, B.C. H.A. Hopkins, R.B. 1980. Mixed prairie I. Am. Birds 34:67—68. Kantrud. 1981. Grazing intensity effects on. the breeding avifauna of North Dakota grasslands. Can. Field-Nat. 95:404417. Jenni, D.A., R.L. Redmond, and T.K. Bicak. 1982. Behavioral ecology and habitat relationships of Long-billed Curlews in western Idaho. Rep. Bur. Land Manage., Boise Idaho. 234pp. j l.A. Ohanjanian. 1985. The Long—billed Curlew, (Numenius status report and americanus), on Skookumchuck Prairie enhancement plan. B.C. Mm. Environ., Wildl. Branch Rep. —  Jensen, H.P., D. Rollins, and R.L. Gillen. 1990. Effects of cattle stock density on trampling loss of simulated ground nests. Wildi. Soc. Bull. 18:71—74. Johnsgard, P.A. 1979. Birds of the Great Plains. Univ. Nebr. Press, Lincoln, Nebr. 539pp. Johnson, D.H. 1972. Breeding bird populations of selected grasslands in east-central North Dakota. Am. Birds 26:971975. j H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. Field— Nat. 95:404—417. 1973. Breeding bird populations of selected grasslands in east-central North Dakota. Am. Birds 27:989990. jn H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. Field Nat. 95:404—417. 90  1974. Breeding bird populations of selected grasslands in east-central North Dakota. Am. Birds 28:1030 1031. .jfl H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. Field—Nat. 95:404—417. Kantrud, H.A. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. Faeld—Nat. 95:404— 417. and R.L. Kologiski. 1982. Effects of soils and grazing on breeding birds on uncultivated upland grasslands of the Northern Great Plains. USD1 Res. Pap. No. 15. J.fl K.D. DeSmet. 1989. Status report on the Long-billed Curlew (Numenius americanus) in Canada. COSEWIC Draft Rep., Dept.Res., Winnipeg, Man. and 1983. Avian associations of the northern Great Plains. J. Biogeo. 10:331—350. Karasiuk, D., H. Vriens, J.G. Stelfox, and J.R. McGillis. 1977. Study results from Suffield, 1976. Pages E33-E44 jfl Effects of livestock grazing on mixed prairie range and wildlife within PFRA pastures, Suffield Military Reserve. J.G. Stelfox, compiler. Range-Wildlife Study Committee, Can. Wildi. Serv., Edmonton, Alta. Kelly, G.D., and W.W. Middlekauff. 1961. Biological studies of Dissosteira surcata Saussure with distributional notes on related California species (Orthoptera: AcrLdidae). Hilgardia 30:395—424. King, R. 1978. Habitat use and related behaviors of breeding Long—billed Curlews. M.S. Thesis, Colorado State Univ., Ft. Collins, Cob. 69pp. Kbopateck, J.M., R.J. Olson, C.J. Emerson, and J.L. Jones. 1979. Land-use conflicts with natural vegetation in the United States. Environ. Sci. Div. Publ. No. 1333, 22pp. Natl. Tech. Inform. Ser., U.S. Dept. Commerce, Springfield, Virginia 22161. j W.D. Graul. 1980. Grassland management practices and bird communities. Pages 38—47 j3 Management of western forest and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT-86, Ogden, Utah. Larson, D.L., and C.E. Bock. 1986. Determining avian habitat preference by bird-centered vegetation sampling. Pages 37-43 .in Wildlife 2000: Modelling habitat relationships for terrestrial vertebrates. J.L. Verner, M.L. Morrison, and C.J. Ralph, eds. Univ. Wisconsin Press, Madison, Wis.  91  Lein, M.R. 1968. The breeding biology of the Savannah Sparrow Passerculus sandwichensis (Gmelin) at Saskatoon, Saskatchewan. M.A. Thesis, Univ. Saskatchewan, Saskatoon. 11 H.A. Kantrud. 1981. Grazing intensity effects on l7lpp. .j the breeding avifauna of North Dakota grasslands. Can. Field— Nat. 95:404—417. Lincoln, P.c. 1925. Notes on the bird life of North Dakota with particular reference to the si.umuer waterfowl. Auk 42:50—64. jfl H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. FieldNat. 95:404—417. Linsdale, J. 1938. Environmental responses of vertebrates in the Great Basin. Am. Midl. Nat. 19:1—206. .j D..E. Medin and W.P. Clary. 1990. Bird and small mammal populations in a grazed and ungrazed riparian habitat in Idaho. U.S.D.A. For. Serv. Intermountain Res. Stn. Res. Pap. INT-425. Little, E.L., Jr. 1977. Research in the pinyon-juniper woodland. Pages 8—19 j E.F. Aldon and T.J. Loring, tech. coord. Ecology, uses and management of pinyon—juniper woodlands: Proceedings of the workshop. USDA For. Serv. Gen. Tech. Pap. RM—39. Magurran, A.E. 1988. Ecological diversity and its measurement. Princeton Univ. Press, Princeton, N.J. l79pp. Maher, W.J. 1973. Birds: I. Population dynamics. Canadian committee for the International Biological Programme. Matador Project, Tech. Rep. 34. H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. Field—Nat. 95:404—417. Matador,  1979. Nestling diets of prairie passerine birds at Saskatchewan, canada. Ibis 121:437—452.  Martin, J.E.H. 1977. The insects and arachnids of Canada: Part 1: Collecting, preparing, and preserving insects, mites, and spiders. Canada Dept. of Agric. Pub. 1643. 182pp. McCallum, D.A., W.D. Graul, and R. Zaccagnini. 1977. The status of the Long-billed Curlew in Montana. Auk 94:599-601. Jn K.D. DeSmet. 1989. Status report on the Long-billed Curlew (Numenius americanus) in Canada. COSEWIC Draft Rep., Dept. Res., Winnipeg, Man. McConnell, S.D., R. Van den Driessche, T.D. Hooper, G.L. Roberts, and A. Roberts. 1994. First occurrence and breeding of Sprague’s Pipit Anthus spragueii, for British Columbia. Can. Field—Nat. 107:222—223. 92  McNicholl, M.K. 1988. Ecological and human influences on Canadian populations of grassland birds. Pages 1-25 Jj 1 Ecology and conservation of grassland birds. P.D. Goriup, ed. International Council for Bird Preservation Tech. Pub. No.7. Meidinger, D. 1987. Recommended vernacular names for common plants of British Columbia. B.C. Mm. For., Res. Branch, Victoria, B.C. 64pp. Moyles. D.L.J. 1981. Seasonal and daily use of plant communities by Sharp—tailed Grouse (Pediocetes Dhasianellus) in the parklands of Alberta. Can. Field—Nat. 95:287—291. Newton, I. 1980. The role of food in limiting bird numbers. Ardea 68:11—30. Nicholson, A., E. Hamilton, W.L. Harper, and B.M. Wikeem. 1991. Bunchgrass zone. Pages 125—137 Jfl D. Meidinger and J. Pojar, compilers and eds. Ecosystems of British Columbia. B.C. Mm. For. Spec. Rep. Ser. 6, Victoria, B.C. Ohanjanian, l.A. 1985. The Long-billed Curlew, (Numenius americanus), on Skookumchuck Prairie status report and enhancement plan. B.C. Mm. Environ., Wildi. Branch Rep. 52pp. —  1986. The Long-billed Curlew in the East Kootenay status report and enhancement schedule for Skookumchuck Prairie. B.C. Mm. Environ., Wildl. Branch Rep. l2pp. —  1987. Status report and management recommendations for the Long—billed Curlew (Numenius americanus) on the Junction. Mm. Environ, and Parks, Wildi. Branch, Williams Lake, B.C. 25pp. Owens, R.A., and M.T. Myres. 1973. Effects of agriculture upon populations of native passerine birds of an Alberta fescue grassland. Can. J. Zool. 51:697—713. Page, J.L., N. Dodd, T.O. Osborne, and J.A. Carson. 1978. The influence of livestock grazing on non—game wildlife. Cal— Neva. Wildl. 1978:159—173. Jj R.A. Ryder. 1980. Effects of Management of grazing on bird habitats. Pages 51-64 western forests and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT-86, Ogden, Utah. Pampush, G.J. 1980. Status report on the Long-billed Curlew in the Columbia and northern Great Basins. Unpub. USFWS Rep., Portland, Ore. j K.D. DeSmet. 1989. Status report on the COSEWIC Long-billed Curlew (Numenius americanus) in Canada. Draft Rep., Dept. Res., Winnipeg, Man. 93  Pepper, G.W. 1972. The ecology of the sharp-tailed grouse during spring and summer in the aspen parkiands of Saskatchewan. Sask. Dept. Nat. Res. Wildi. Rep. No. 1. Potter, P.E. 1972. Territorial behavior in Savannah Sparrows in southeastern Michigan. Wilson Bull. 84:48-59. .in H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. Field—Nat. 95:404417. Rand, A.L. 1948. Birds of southern Alberta. Nat. Mus. Can. Bull. 111. H.A. Kantrud. 1981. Grazing intensity effects on the breeding avifauna of North Dakota grasslands. Can. FieldNat. 95:404—417. Redmond, R.L., T.K. Bicak, and D.A. Jenni. 1981. An evaluation of breeding season census techniques for Long—billed Curlews (Numenius americanus). Pages 197-201 .jj Estimating numbers of terrestrial birds. C.J. Ralph, ed. Studies in avian biology. No. 6. 197—201. jfl I. A. Ohanjanian. 1985. The Long—billed Curlew, (Numenius americanus), on Skookumchuck status report and enhancement plan. B.C. Mm. Prairie Environ., Wildi. Branch Rep. —  and D.A. Jenni. 1985. Note on the diet of Longbilled Curlew chicks in western Idaho. Great Basin Nat. 45: 85—86. and 1986. Population ecology of the Long—billed Curlew (Numenius americanus) in western Idaho. Auk 103:755—767. Redpath, K. 1990. Identification of relatively undisturbed areas in the South Okanagan. Canadian Wildlife Service, Delta, B.C. jj 1 W.L. Harper, E.C. Lea, and R.E. Maxwell. 1992. Biodiversity inventory in the South Okanagan. B.C. Mm. Environ., Wildlife Branch, Victoria, B.C. l6pp. Reed, J.M. 1986. Vegetation structure and Vesper Sparrow territory location. Wilson Bull. 98:144—147. Renaud, W.E. 1980. The Long-billed Curlew in Saskatchewan: status and distribution. Blue Jay 38:221-237. .j K.D. DeSmet. 1989. Status report on the Long-billed Curlew (Numenius americanus) in Canada. COSEWIC Draft Rep., Dept. Res., Winnipeg, Man. Renken, R.B., and J.J. Dinsmore. 1987. Nongame bird communities on managed grasslands in North Dakota. Can. Field—Nat. 101:551—557.  94  Roberts, A. 1992. A report on the ecology of the Junction Wildlife Management Area. B.C. Mm. Environ., Wildl. Branch, Williams Lake, B.C. 63pp. 1994. Biodiversity. B.C. Mm. Environ., Lands, and Parks, Wildi. Branch, Williams Lake, B.C. Rogers, L., R. Lavigne, and J.L. Miller. 1972. Bioenergetics of the western harvester ant in the shortgrass plains ecosystem. Environ. Entomol. 1:763—768. Rotenberry, J.T. 1980. Dietary relationships among shrubsteppe passerine birds: competition or opportunism in a variable environment? Ecol. Monogr. 50:93—110. and J.A. Wiens. 1978. Nongame bird communities in northwestern rangelands. Pages 32—46 j Workshop on nongame bird habitat management in the coniferous forests of the western United States. R.M. DeGraff, ed. USDA For. Serv. Gen. Tech. Rep. PNW-64. and 1980. Habitat structure, patchiness, and avian communities in North American steppe vegetation: a multivariate analysis. Ecology 6:1228-1250. Roth, R.R. 1977. The composition of four bird communities in south Texas brush-grasslands. Condor 79:417-425. Ryder, R.A. 1980. Effects of grazing on bird habitats. Pages 5164 .j Management of western forests and grasslands for non— game birds. U.S. For. Serv. Gen. Tech. Rep. INT—86, Ogden, Utah. Sadler, D.A.R. and W.J. Maher. 1976. Notes on the long—billed curlew in Saskatchewan. Auk 93:382—384. Sas Institute, Inc.  1989. SAS. Cary, N.C.  Shotwell, R.L. 1958. The grasshopper your sharecropper. Univ. Missouri Agr. Exp. Stn. Bull. 714. l6pp. Skinner, R.M. 1975. Grassland use pattern and prairie bird populations in Missouri. Pages 171—180 .jfl M.K. Wali, ed. Prairie: A multiple review. Univ. North Dakota Press, Grand Forks, N.D. Smith, C.C. 1940. The effect of overgrazing and erosion upon the biota of the mixed-grass prairie of Oklahoma. Ecol. 21:381397.  95  Springfield, H.W. 1976. Characteristics and management of southwestern pinyon—juniper ranges: the status of our USDA For. Serv. Res. Pap. RM—160. knowledge. Southwood, T.R.E. 1978. Ecological methods: with particular reference to the study of insect populations. Second ed. Chapman and Hall, London. 524pp. Sugden, J.W. 1933. Range restriction of the Long-billed Curlew. Condor 35:3-9. Systat, Inc. IL.  1991. SYSTAT: The system for statistics. Evanston,  Taylor, R.L., and B. MacBryde. 1977. Vascular plants of British Columbia: a descriptive resource inventory. Univ. B.C. Tech. Bull. No. 4. Univ. B.C. Press, Vancouver, B.C. 754pp. Terres, J.K. 1980. The Audubon Society encyclopedia of North American birds. Alfred A. Knopf, New York. llo9pp. Tester, J.R., and W.H. Marshall. 1961. A study of certain plant and animal interrelationships on a native prairie in northwestern Minnesota. Occas. Pap. Minn. MUS. Nat. Hist. 8:1—51. in R.A. Owens and M.T. Myres. 1973. Effects of agriculture upon populations of native passerine birds of an Alberta fescue grassland. Can. J. Zool. 51:697—713. Townsend, J.E., and P.J. Smith. 1977. Proceedings of the seminar on improving fish and wildlife benefits in range management. USD1 Fish and Wildl. Serv. Prog., Washington, D.C. FWS/OBS 77/1. Ji R.A. Ryder 1980. Effects of grazing on bird habitats. Pages 51—64 ilL Management of western forests and grasslands for non—game birds. USDA For. Serv. Gen. Tech. Rep. INT—86. Trost, C.H. 1972. Adaptations of Horned Larks (Eremohila alpestris) to hot environments. Auk 80:506-527. Van den Driessche, R., S.D. McConnell, and T.D. Hooper. In Press. First breeding record of the Upland Sandpiper Bartramia loncicauda, for British Columbia. Can. Field—Nat. Verner, J. 1985. Assessment of counting techniques. Pages 247-302 Current ornithology. R.P. Johnston, ed. Vol. 2. Plenum Pub. Co., New York. Whittaker, R.H., and G.M. Woodwell. 1972. Evolution of natural communities. Pages 137—159 j Ecosystem structure and function. J.A. Wiens, ed. Oregon State Univ. Press, Corvallis, Ore. Jj J.A. Wiens. 1973. Pattern and process in grassland bird communities. Ecol. Monogr. 43:237—270. 96  Wiens, J.A. 1969. An approach to the study of ecological relationships among grassland birds. Ornith. Monogr. 8:1-93. .jfl J.A. Wiens. 1973. Pattern and process in grassland bird communities. Ecol. Monogr. 443:237—270. 1973a. Interterritorial habitat variation in Grasshopper and Savannah Sparrows. Ecology 54:877—884. 1973b. Pattern and process in grassland bird communities. Ecol. Monogr. 443:237-270. l974a. Climatic instability and the “ecological saturation” of bird communities in North American grasslands. Condor 76:385—400. 1974b. Habitat heterogeneity and avian community structure in North American grasslands. Am. Midland Nat. 91:195—213. 1975. Avian communities, energetics, and functions in coniferous forest habitats. Pages 146-182 .jn Proceedings of the symposium on management of forest and range habitats for nongame birds. Dixie R. Smith, tech. coord. USDA For. Serv., Wash., D.C. 1976. Population responses to patchy environments. Ann. Rev. Ecol. Syst. 7:81-120. .jfl R.A. Ryder 1980. Effects Management of of grazing on bird habitats. Pages 51-64 western forests and grasslands for non—game birds. U.S. For. Serv. Gen. Tech. Rep. INT-86, Ogden, Utah. .  1977. Model estimation of energy flow in North American grassland bird communities. Oecologia 31:135—151. and M.I. Dyer. 1975. Rangeland avifauna: their composition, energetics and role in the ecosystem. Pages 146—181 jj Symposium on management of forest and range habitats for nongame birds, Tucson, Arizona. USDA For. Serv. Gen. Tech. Rep. WO-l. and J.T. Rotenberry. 1979. Diet niche relationships among North American grassland and shrubsteppe birds. Oecologia 42:253—292. and 1981. Habitat associations and community structure of birds in shrubsteppe environments. Ecol. Monogr. 51: 21—41. and 1985. Response of breeding passerine birds to rangeland alteration in North American shrubsteppe locality. J. Applied Ecol. 22:655—668. 97  World Wildlife Fund Canada. 1989. Prairie conservation action plan: 1989—1994. World Wildlife Fund Canada, Toronto, Ontario. 38pp. Wray, T., and R.C. Whitiuore. 1979. Effects of vegetation on nesting success of Vesper Sparrows. Auk 96:802—805.  98  Appendix 1.  Bird species censused in the Chilcotin study area, British Columbia, 1991/92.  Common Name  Taxonomic Name  Common Loon Great Blue Heron Canada Goose Green-winged Teal Mallard Northern Pintail Blue-winged Teal Northern Shoveler Gadwal 1 Lesser Scaup White-winged Scoter Barrow’ s Goldeneye Bufflehead Common Merganser Bald Eagle Northern Harrier Sharp-shinned Hawk Northern Goshawk Red-tailed Hawk American Kestrel Merlin Gyrfalcon Blue Grouse Ruf fed Grouse Sharp-tailed Grouse Virginia Rail Sora Sandhill Crane Killdeer Greater Yellowlegs Lesser Yellowlegs Spotted Sandpiper Upland Sandpiper Long-billed Curlew Common Snipe Black Tern Mourning Dove Great Horned Owl Short-eared Owl Calliope Hummingbird Rufous Hummingbird Lewis’ Woodpecker Red-naped Sapsucker Downy Woodpecker Hairy Woodpecker Northern Flicker Olive-sided Flycatcher  Gavia iimiier Ardea herodias Branta canadensis Anas crecca Anas platyrhynchos Anas acuta Anas discors Anas clveata Anas strepera Aythva affinis Melanitta fusca Bucehala islandica Bucehala albeola Mergus merganser Hal iaeetus leucocephalus Circus cyaneus Accipiter striatus Accipiter qentilis Buteo lamaicensis Falco sparverius Falco columbarius Falco rusticolus Dendracrapus obscurus Bonasa u!nbellus Tympanuchus phasianellus Rallus limicola Porzana carolina Grus canadensis Charadrius vociferus Trincra melanoleuca Tringa flavipes Actitis inacularia Bartramia lonciicauda Numenius americanus Gallinago crallinago Chlidonias niger Zenaida macroura Bubo vircrinianus Asio flammeus Stellula calliope Se1ashorus rufus Melanerpes lewis Sphyrapicus ruber Picoides pubescens Picoides villosus Colates auratus Contous borealis 99  Appendix 1. cont. Common Name  Taxonomic Name  Western Wood—pewee Alder Flycatcher Willow Flycatcher Least Flycatcher Dusky Flycatcher Pacific-slope Flycatcher Say’s Phoebe Western Kingbird Horned Lark Tree Swallow Violet-green Swallow Northern Rough-winged Swallow Cliff Swallow Barn Swallow Black-billed Magpie American Crow Common Raven Black-capped Chickadee Mountain Chickadee Red-breasted Nuthatch House Wren Marsh Wren Ruby-crowned Kinglet Mountain Bluebird Veery Hermit Thrush American Robin Sprague’s Pipit European Starling Warbling Vireo Orange—crowned Warbler Yellow Warbler Yellow-rumped Warbler Northern Waterthrush Wilson’s Warbler Western Tanager Lazuli Bunting Chipping Sparrow Clay—coloured Sparrow Brewer’s Sparrow Vesper Sparrow Savannah Sparrow Lincoln’s Sparrow Golden—crowned Sparrow White—crowned Sparrow Red-winged Blackbird Western Meadowlark Yellow—headed Blackbird  Contopus sordidulus EmDidonax alnorum Empidonax traillii EmDidonax minimus Empidonax oberholseri Empidonax difficilis Savornis sava Tyrannus verticalis Eremophila alpestris Tachycineta bicolor Tachycineta thalassina Stelcridopteryx serriennis Hirundo pvrrhonota Hirundo rustica Pica pica Corvus brachvrhvnchos Corvus corax Parus atricapillus Parus qambeli Sitta canadensis Troglodytes aedon Cistothorus palustris Regulus calendula Sialia currucoides Catharus fuscescens Catharus cruttatus Turdus micrratorius Anthus spracrueii Sturnus vuicTaris Vireo gilvus Vermivora celata Dendroica petechia Dendroica coronata Seiurus noveboracensis Wilsonia pusilla Pirancra ludoviciana Passerina amoena Spizella passerina Spizella pallida Spizella breweri Pooecetes crramineus Passerculus sandwichensis Melospiza lincolnii Zonotrichia atricapilla Zonotrichia leucophrvs Acrelaius phoeniceus Sturnella necriecta Xanthocephalus xanthocehalus 100  Appendix 1. cont. Common Name  Taxonomic Name  Brewer’s Blackbird Brown-headed Cowbird Red Crossbill Pine Siskin  EuDhagus cyanoceha1us Molothrus ater Loxia curvirostra Carduelis minus  101  Appendix 2. Bird species and habitat variable codes.  Bird species HOLA VESP LBCU WEME BRBL TRES MOBL SAVS UPSA SPPI BRSP STGR SEOW  horned lark vesper sparrow long-billed curlew western meadowlark Brewer’s blackbird tree swallow mountain bluebird savannah sparrow upland sandpiper Sprague’s pipit Brewer’s sparrow sharp-tailed grouse short-eared owl  — — — — — -  Habitat variables MAYVGCOV vegetation cover in May MAYVGHT vegetation height in May JUNVGCOV vegetation cover in June JUNVGHT vegetation height in June BAREGRND % cover of bare ground GRASS % cover of grass LITTER % cover of litter SHRUBS % cover of shrubs TREES % cover of trees TREES_O number of trees in the point—count area BGRNDHI heterogeneity index for % cover of bare ground MAYCOVHI heterogeneity index for % vegetation cover in May MAYHTHI heterogeneity index for vegetation height in May JUNHTHI heterogeneity index for vegetation height in June ELEV elevation SPRNGAUM number of spring grazing AUM5 SMMERAUM number of summer grazing AUMs FALLAUM number of fall grazing AUMS -  -  -  -  -  -  -  -  — -  -  -  -  -  -  102  Appendix 3.  Plant species recorded in the Chilcotin study area, British Columbia, 1992.  Taxonomic Name  Common Name  Achillea millefolium Aqoseris alauca var. dasycephala Aaropvron cristatum Aarovron sicatum Acrropvron trachycaulum Allium cernum Androsace septentrional is Anemone multifida Antennaria dimorpha Antennaria microphylla Antennaria parviflora Antennaria umbrinella Arabis holboellii Artemisia campestris Artemisia dracunculus Artemisia friciida Astragalus acirestis Astracialus miser Astragalus tenellus Balsamorhiza sagittata Bromus inermis Bromus tectorum Calochortus macrocarpus Carex spp. Cerastium arvense Chrysothamnus nauseosus var. albicaulis Cirsium undulatum Comandra umbellata Crepis atrabarba Distichlis stricta Erigeron compositus var. cilabratus Erigeron flaciellaris Erigeron linearis Erigeron speciosus var. sieciousus Erioqonum heracleoides Festuca saximontana Gaillardia aristata Galium boreale Geranium viscosissimum var. viscosissimum Grindelia squarrosa Hedysarum boreale ssp. mackenzii Koeleria macrantha Lappula redowskii var. redowskii Linum perenne ssp. lewisii Lithospermum ruderale  yarrow short—beaked agoseris crested wheatgrass bluebunch wheatgrass slender wheatgrass nodding oflion northern fairy—candelabra cut—leaved anemone low pussytoes rosy pussytoes Nuttall ‘S pussytoes umber pus sytoes Hoelboell’s rockcress northern wormwood tarragon prairie sagewort field milk—vetch timber milk-vetch pulse milk-vetch arrow—leaved balsamroot smooth brome cheatgrass sagebrush mariposa lily sedge spp. field chickweed  103  rabbit-brush wavy-leaved thistle pale comandra slender hawksbeard alkali saltgrass cut—leaved daisy trailing fleabane line-leaved daisy showy daisy parsnip—flowered buckwheat Rocky Mountain fescue brown—eyed Susan northern bedstraw sticky purple geranium curly—cup gumweed northern hedysarum 5 unegrass western stickseed western blue flax lemonweed  Appendix 3. cont.  Taxonomic Name  Common Name  Lomatium macrocarpum Opuntia fragilis Orthocarus luteus Penstemon procerus var. procerus compressa Poa iuncifolia £2 pratensis Poa sandbergii Potentilla gracilis Potentilla hippiana Rosa acicularis Rosa nutkana Senecio canus Silene drummondii var. drummondii Sisyrinchium montanum Sd idacio spathulata Spartina ciracilis Sorobolus cryptandrus Stipa comata Stipa occidentalis Stipa richardsonii Stipa spartea Symphoricarpos occidental is Tracioocion dubius Tracioocion pratens is Z ipadenus venenosus  large-fruited desert-parsley brittle prickly-pear cactus yellow owl—clover small flowered penstemon Canada bluegrass alkali bluegrass Kentucky bluegrass Sandberg’ s bluegrass graceful cinquefoil woolly cinquefoil prickly rose Nootka rose woolly groundsel Drummond’s ,ampion mountain blue—eyed—grass spike-like goldenrod alkali cordgrass sand dropseed needle—and—thread grass stiff needlegrass spreading needlegrass porcupine grass western snowberry yellow salsify meadow salsify meadow death—camas  104  —  kppendix 4.  : 0 H Ha:  Chi-square analysis of habitat structural use among horned larks, vesper sparrows, western meadowlarks, and mountain bluebirds in the Chilcotin study area, British Columbia, 1991/92.  There is no difference in habitat structural use among the four bird species. Habitat structural use is different among the four bird species.  Species  Total  Habitat structure type Rocks  Shrubs  Trees  Fences  Logs  Roads  HOLA 8 1 f b 1 F  690 358  17 142  9 245  9 68  24 19  214 132  963  VESP f. F.  277 454  321 179  347 311  114 86  20 24  142 167  1221  WEME f. F.  72 183  61 72  303 125  15 34  9 10  32 68  492  MOBL f. 1 F  32 76  24 30  74 52  64 14  4 4  7 28  205  1071  423  733  202  57  395  2881  Total 1)  Observed frequency Expected frequency = 1530.6 2 X 5 )=1530.6<0.001) 1 ( 2 P(X  0 Therefore, reject H  105  Chi-square analyses of habitat structural use by horned larks, vesper sparrows, western meadowlarks, and mountain bluebirds in the Chilcotin study area, British Columbia, 1991/92.  Appendix 5.  There is no difference between proportions of habitat structures available and those used by each bird species. Proportions of habitat structures available and used by each bird species are different.  : 0 H Ha:  Total  Habitat structure type (proportion available)  Species  Trees Rocks Shrubs (0.503) (0.329) (0.118)  Roads Logs Fences (0.003) (0.028) (0.017)  HOLA fa  690 484.4  b 1 F  2 x  2862.1  =  VES P f1 F  2 x  WEME 1 f 1 F  2 x  MOBL f. F.  = 2 x 8  I)  1530.6  321 401.7  114 3.7  347 144.1  61 161.9  303 58.1  24 67.4  15 1.5  )=1530.6<0.001) 5 ( 2 P(X  Observed frequency Expected frequency  106  142 20.8  for  H0  1221  9 13.8  492  32 8.4  0 Therefore, reject H Western Meadowlarks  64 0.62  74 24.2  20 34.2  963  214 16.4  0 for Therefore, reject H Vesper Sparrows  )=l409.1<0.001) 5 ( 2 P(X  32 103.1  24 30.0  Therefore, reject Horned Larks  )=4487.2<0.001) 5 ( 2 P(X  72 124.4  1409.1  =  9 2.9  9 113.6  )=2862.l<0.OO1) 5 ( 2 P(X  277 614.2  4487.2  =  17 316.8  4 5.7  205  7 3.5  Therefore, reject Mountain Bluebirds  for  H0  for  Appendix 6.  Multiple correlations between vegetation structure and topographic features for the Chilcotin study area, British Columbia, 1991/92.  Topographic Features Vegetation Structure MAYVGCOV MAYVGHT JUNVGCOV JUNVGHT BAREGRND GRASS LITTER SHRUBS TREES TREES_O MAYCOVHI MAYHTHI JUNHTHI BGRNDHI variability explained  Elevation  Slope  Aspect  0.11 0.02 —0.05 —0.14 —0.27 0.18 0.26 —0.80 0.15 0.07 —0.47 —0.36 —0.41 0.14  0.15 0.22 0.31 0.31 0.15 —0.19 —0.22 0.80 —0.11 0.16 0.48 0.45 0.45 —0.04  0.48 0.46 0.43 0.32 —0.01 —0.36 0.20 0.17 0.42 0.12 0.05 005 0.15 0.39  10%  12%  9%  107  Appendix 7.  Multiple correlations between vegetation structure and seasonal grazing (AUMs) for the Chilcotin study area, British Columbia, 1991/92. Grazing Levels  Vegetation Structure MAYVGCOV MAYVGHT JUNVGCOV JUNVGHT BAREGRND GRASS LITTER SHRUBS TREES TREES_O MAYCOVHI MAYHTHI JUNHTHI BGRNDHI variability explained  SPRING-AU!’!  SUNNER-AUM  FALL-AUM  —0.24 —0.27 —0.22 —0.21 0.42 —0.49 —0.35 0.05 —0.20 —0.06 0.01 —0.13 —0.05 —0.30  —0.15 —0.18 —0.20 —0.24 0.41 —0.34 —0.26 —0.22 —0.12 0.02 —0.13 —0.23 —0.22 —0.17  —0.10 —0.14 —0.12 —0.19 0.37 —0.39 —0.28 —0.20 —0.12 0.13 —0.13 —0.22 —0.22 —0.18  7%  5%  5%  108  

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.831.1-0087683/manifest

Comment

Related Items