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Environmental contaminants, disturbance and breeding failure at a great blue heron colony on Vancouver… Moul, Ian E. 1990

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ENVIRONMENTAL CONTAMINANTS, DISTURBANCE AND BREEDING FAILURE AT A GREAT BLUE HERON COLONY ON VANCOUVER ISLAND By IAN E. MOUL B.Sc.(agr), University of B r i t i s h Columbia, 1987 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTERS OF SCIENCE i n THE FACULTY OF GRADUATE STUDIES (Department of Animal Science) we accept t h i s thesis as conforming to the required standard THE UNIVERSITY OF BRITISH COLUMBIA September 13, 1990 ® Ian E. Moul, 1990 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. Department of The University of British Columbia Vancouver, Canada DE-6 (2/88) i i ABSTRACT Great Blue Herons (Ardea herodias) breeding near a pulp m i l l at Crofton B . C . f a i l e d to r a i s e young i n 1987 and 1988. Elevated l e v e l s of po lych lor inated dibenzo-p-dioxins and po lych lor inated dibenzo-furans were detected i n t h e i r eggs. The highest 2 ,3 ,7 ,8 - t e t rach lorod ibenzo-p-d iox in (TCDD) t o x i c equivalent l e v e l observed was 496 ng/kg (wet weight) i n 1987 ( E l l i o t t et al. 1989). I compared the Crofton colony with a l ess contaminated colony on Sidney Is land i n 1988 and 1989. I examined three poss ib le explanations for nest ing f a i l u r e : (i) abnormal nest ing behaviour by parents because of contamination, ( i i ) disturbance by human a c t i v i t i e s , and ( i i i ) predat ion by Bald Eagles (Haliaeetus leucocephalus), Northwestern Crows (Corvus caurinus) and Common Ravens (Corvus corax). The Crofton colony was successful i n 1989 and 1990. Within the TCDD t o x i c equivalent range of 34 - 257 ng/kg (1989), I observed no abnormal heron nest ing behaviour or reduct ion i n numbers of chicks f ledged. In 1988 the herons at Crofton were disturbed repeatedly by human a c t i v i t i e s . Bald Eagles were observed d a i l y at both Crofton and Sidney I s land . The heron colony on Sidney Is land f a i l e d i n 1989 and 1990. The f a i l u r e s on Sidney Is land were thought to involve a disturbance by eagles followed by rapid removal of eggs and young chicks at unattended nests by crows and ravens. I t i s l i k e l y that disturbance and predation played a part i n the f a i l u r e at Crofton i n 1988, but there remains the p o s s i b i l i t y that environmental contaminants may have increased the s e n s i t i v i t y of herons to disturbance and predation. i v Abstract L i s t of Tables L i s t of Figures Acknowledgements Introduct ion Methods Results Discuss ion L i t e r a t u r e Ci ted TABLE OF CONTENTS PAGE i i v v i v i i 1 9 22 44 52 V L I S T OF TABLES T A B L E PAGE 1) P r o d u c t i o n o f y o u n g h e r o n s a t C r o f t o n , 23 Hammond B a y , H o l d e n L a k e a n d S i d n e y I s l a n d h e r o n c o l o n i e s f r o m 1986 t o 1 9 9 0 . 2) N e s t a t t e n d a n c e d u r i n g t h e i n c u b a t i o n p e r i o d a t 29 t h e C r o f t o n a n d S i d n e y I s l a n d h e r o n c o l o n i e s . 3) P r o d u c t i o n o f e g g s a n d y o u n g , i n f i v e h e r o n n e s t s 33 a t C r o f t o n i n 1 9 8 9 , c o m p a r e d w i t h l e v e l s o f 2 , 3 , 7 , 8 TCDD a n d TCDD t o x i c e q u i v a l e n t s f o u n d i n t h e i r e g g s . 4) O c c u r r e n c e o f B a l d E a g l e s a t C r o f t o n a n d S i d n e y 36 I s l a n d h e r o n c o l o n i e s , p e r h o u r o f o b s e r v a t i o n , M a r c h t h r o u g h J u l y 1988 a n d 1 9 8 9 . 5) F r e q u e n c i e s o f h e r o n - e a g l e i n t e r a c t i o n s , a n d 37 e a g l e p r e s e n c e a t G r e a t B l u e H e r o n c o l o n i e s . 6) R e s p o n s e s o f h e r o n s t o t h e p r e s e n c e o f e a g l e s 39 n e a r t h e C r o f t o n a n d S i d n e y I s l a n d h e r o n c o l o n i e s . 7) F r e q u e n c y o f c r o w a n d e a g l e o c c u r r e n c e s a t t h e 41 C r o f t o n h e r o n c o l o n y i n 1 9 8 9 . 8) F r e q u e n c y o f c r o w a n d r a v e n s i g h t i n g s a t t h e 42 C r o f t o n h e r o n c o l o n y d u r i n g i n c u b a t i o n a n d c h i c k s t a g e s . v i L I S T OF F I G U R E S FIGURE PAGE 1) Location of Great Blue Heron breeding colonies 11 studied. 2) Locations of Great Blue Heron breeding colonies 12 at each study s i t e . 3) Levels of 2378 TCDD and TCDD to x i c equivalents i n 28 Great Blue Heron eggs c o l l e c t e d at Crofton and on Sidney Island 1986 - 1989. 4) Percent of time Great Blue Herons spent incubating 30 at Crofton and on Sidney Island i n 1988 and 1989. 5) Percent of time Great Blue Herons i n f i v e nests at 32 Crofton i n 1989, spent incubating, compared to TCDD tox i c equivalent l e v e l s i n a sample of t h e i r eggs. v i i ACKNOWLEDGMENTS I wish t o thank my t h e s i s committee, Kimberly M. Cheng, L e s l i e E. Hart and James N.M. Smith f o r a s s i s t a n c e and ad v i c e throughout t h i s p r o j e c t . Very s p e c i a l thanks go t o Robert W. B u t l e r f o r u n l i m i t e d encouragement, a d v i c e and a s s i s t a n c e i n a l l aspects o f t h i s r e s e a r c h . Major fun d i n g f o r t h i s p r o j e c t was p r o v i d e d by the World W i l d l i f e Fund Canada - W i l d l i f e T o x i c o l o g y Fund. Support i n k i n d was r e c e i v e d from Canadian W i l d l i f e S e r v i c e (R.W. B u t l e r and P.E. Whitehead), B.C. F o r e s t Products and F l e t c h e r Challenge Canada (Arvind Thakore and D e r i k H i l l ) . I a l s o r e c e i v e d support from the Anne V a l l e e E c o l o g i c a l Fund, the Cowichan V a l l e y N a t u r a l i s t s S o c i e t y , and G.E. Moul. B.C. F o r e s t P r o d u c t s / F l e t c h e r Challenge k i n d l y p r o v i d e d p e r m i s s i o n t o observe the C r o f t o n heron colony. B.C. P r o v i n c i a l Parks p r o v i d e d p e r m i s s i o n t o study herons a t the Sidney S p i t Marine Park. Thanks t o Jack Knighton, Stan Thomas and the s t a f f a t Tamagawa Gakuen f o r p e r m i s s i o n t o v i s i t heron c o l o n i e s on t h e i r p r o p e r t i e s . A s s i s t a n c e i n f i e l d s t u d i e s were made by A.M. B r e a u l t , R.W. B u t l e r , C. Maurice, L.M. N i c h o l , T.M. S u l l i v a n and K. Tremaine. R.J. Norstrom and P.E. Whitehead p r o v i d e d data on contaminant l e v e l s . 1 I N T R O D U C T I O N Southern Vancouver Island i s separated from mainland B r i t i s h Columbia by the S t r a i t of Georgia, which supports a diverse ecosystem, including 2,000 - 3,000 Great Blue Herons (Butler 1989; P.E. Whitehead pers. comm.)- The shores of the s t r a i t also have one of the highest concentrations of forest product industries i n Canada ( E l l i o t t et al. 1989). In 1987 the Canadian W i l d l i f e Service (CWS) analyzed eggs from four heron colonies i n the S t r a i t of Georgia and found polychlorinated dibenzo-p-dioxin (PCDD) and polychlorinated dibenzo-furan (PCDF) contamination ( E l l i o t t et al. 1989). Eggs from a colony near the town of Crofton, and a k r a f t pulp and paper m i l l , contained higher l e v e l s of PCDDs than eggs from other heron colonies i n the S t r a i t . The mean l e v e l of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) i n the Crofton eggs was three times higher i n 1987 (210 ng/kg or 210 ppt) than i n 1986 (66 n g / k g ) ( E l l i o t t et al. 1989). The Crofton heron colony f a i l e d to produce any young i n 1987 although some were successful i n 1986 (P.E. Whitehead, pers. comm.). 2 PCDD and PCDF contamination i n the S t r a i t of Georgia PCDDs and PCDFs are organochlorines, a group of organic , fa t so luble , synthet ic chemicals containing one or more ch lor ine atoms (Bumb et al. 1980). Organochlorines that occur i n r i n g s tructures , such as d i c h l o r o d i p h e n y l -tr i ch loroethane (DDT), po lych lor inated biphenyl (PCB), PCDD and PCDF, are s table , pers i s t ent i n the environment and can i n t e r a c t with enzymes i n b i o l o g i c a l systems to cause adverse e f fec ts (Kubiak et al. 1983; Mineau et al. 1984; Risebrough 1986). PCDDs and PCDFs are formed during the bleaching of wood pulp by the k r a f t process and are released i n pulp m i l l e f f luent (Swanson et al. 1988). Chlorophenols, used as a wood preservat ive by the forest industry , a l so contain trace amounts of PCDDs and PCDFs and are a d d i t i o n a l sources of environmental contamination (Miles et a l . 1985). Another s i g n i f i c a n t source of PCDDs i s the f l y ash from municipal refuse inc inera tors (Karasek and Dickson 1987). The most b i o l o g i c a l l y t o x i c , and one of the most s table of these compounds, i s TCDD (Courtney and Moore 1971)(see a lso review on page 4) . In the S t r a i t of Georgia, s i x pulp and paper m i l l s discharge p o t e n t i a l l y contaminated waste. In a d d i t i o n , the Fraser River flows into the s t r a i t containing the e f f luent 3 of four i n t e r i o r pulp m i l l s . Added to t h i s are the combined e f f luent of numerous saw m i l l s , wood treatment p lant s , small i n d u s t r i e s , a g r i c u l t u r a l runoff and the municipal o u t f a l l of several c i t i e s and m u n i c i p a l i t i e s . When organochlorines enter the aquatic environment they are e i t h e r destroyed, dispersed or concentrated. Of a l l known organochlorines , PCDDs are among the l eas t so luble and the most r e s i s t a n t to degradation (Schroy et al. 1985). Geochemical accumulation occurs when hydrophobic chemicals become p o s i t i v e l y adsorbed to s i l t and c lay p a r t i c l e s i n the water (Haque et al. 1911; Leidy 1980). Suspended sediments scavenge organochlorines from water, concentrat ing them many times over t h e i r aqueous s o l u b i l i t y l i m i t (Duke 1977). As fresh water enters an estuary, suspended p a r t i c l e s f l o c c u l a t e and s e t t l e (Hobbie and Copeland 1980). The net r e s u l t i s an accumulation of organochlorines along with the nutr ients which support the abundance of p lants and animals usua l ly found i n e s tuar ies . PCDD, PCDF and other organochlorines enter the biosphere by adhering to the surfaces of algae and p lant secret ions (Matsumura 1977). This p lant matter i s then consumed by invertebrates and f i s h (Matsumura 1977; Hobbie and Copeland 1980). Great Blue Herons, being near the top of the food chain , receive organochlorines that have been 4 concentrated through successive t roph ic l e v e l s . Woodwell et al. (1967) reported that tox in l e v e l s i n f i s h - e a t i n g b i r d s concentrated more than one and a h a l f m i l l i o n times compared to the surrounding environment. Fa t - so lub le t o x i c compounds may concentrate to even greater l eve l s (Hunt and Bischof f 1960). E l l i o t t et al. (1989) reported high concentrations of PCDDs and PCDFs i n heron eggs from colonies near the Fraser River estuary and t i d a l mudflats adjacent to the e f f luent discharge from the Crofton pulp m i l l . Eggs from heron co lonies near Boundary Bay and Sidney I s land , locat ions r e c e i v i n g very l i t t l e i n d u s t r i a l discharge, had very low contaminant l e v e l s . Organochlorines and Avian Reproduction Previous to the 1987 f a i l u r e of the Crofton heron colony ( E l l i o t t et al. 1989; Whitehead 1989) there has been no report i n the l i t e r a t u r e l i n k i n g PCDDs or PCDFs with heron reproduct ion. Corre la t ions between egg s h e l l th inn ing , embryonic mor ta l i t y and heron reproductive success, with other organochlorines and by heavy metals have been we l l documented ( M i l s t e i n et al. 1970; Pres t t 1970; Vermeer and Reynolds 1970; Faber et al. 1972; Blus et a l . 1980; Laporte 1982; Blus et al. 1985; Henny et a l . 1985; F indhol t and 5 Trost 1985; F i t z n e r et al. 1988). While heron eggs from Crofton contained a v a r i e t y of contaminants ( E l l i o t t et al. 1989; Whitehead 1989), when compared with contaminants l e v e l s found i n eastern Canada, only the l e v e l s of PCDDS and PCDFs were at concentrations high enough to c u r r e n t l y cause concern ( P . E . Whitehead, pers . comm.). There i s evidence that PCDDs and PCDFs may cause reproduct ive f a i l u r e i n some avian species . Poor reproductive success i n Herring G u l l (Larus argentatus) populations i n the Great Lakes i n the ear ly 1970s was suspected to be the r e s u l t of high concentrations of d ich loro-d iphenyld ich loroethy lene (DDE), PCB and TCDD (Fox et al. 1978, Gilman et al. 1978 and Mineau et al. 1984). These g u l l s had reduced nest attentiveness (nest defence and amounts of time spent incubat ing) , high embryonic m o r t a l i t y and egg-she l l th inn ing . Hoffman et al. (1987) a r t i f i c i a l l y incubated F o r s t e r ' s Tern (Sterna forsteri) eggs c o l l e c t e d i n Green Bay, Lake Michigan. This colony had a h i s t o r y of poor reproduct ive success and was known to be contaminated with r e l a t i v e l y high l eve l s of PCDDs, PCDFs and PCBs (see Kubiak et al. 1989). The t ern eggs had a 50% lower hatching rate i n the laboratory and showed a higher rate of mutations (17% for hatchl ings and embryos) compared to uncontaminated eggs. In England, M i l s t e i n et al. (1970) observed aberrant behaviours i n one adult male Grey Heron (Ardea cinerea) from 6 a populat ion contaminated with DDE and d i e l d r i n . This heron repeatedly stabbed and destroyed the eggs wi th in i t s nest . This same heron was extremely ina t tent ive i n both guarding i t s nest and incubating the eggs. However, the l e v e l s of toxins i n t h i s b i r d were not determined. Because minute quant i t i e s of organochlorines (parts per b i l l i o n or parts per t r i l l i o n ) cause b i o l o g i c a l problems, and a large v a r i e t y of man-made chemicals pervade the environment, i t i s extremely d i f f i c u l t to assign cause and e f fec t to a s ing le chemical or chemical isomer. Laboratory s tudies have demonstrated the disparate e f fec t s of s p e c i f i c organochlorines on b i r d s . For example, Ring Doves (Streptopelia risoria) fed a d i e t containing PCB ( a r o c l o r ® 1254) had increased embryonic morta l i ty and reduced incubat ion behaviour (Peakall and Peakal l 1973). Brunstrom (1988) in jec ted eggs of four species; s i x s t r a i n s of Domestic Chickens (Gallus gallus), Domestic Goose (Anser anser), Mal lard (Anas platyrhynchos) and Herr ing G u l l , with 3 , 3 1 , 4 , 4 1 - t e t r o c h l o r o b i p h e n y l (TCB) a compound of s i m i l a r s tructure and binding propert ies as TCDD. Chicken embryonic m o r t a l i t y was s i g n i f i c a n t l y higher than contro l chickens i n f i v e out of s ix s t r a i n s . Examination of the chicken embryos revealed subcutaneous edema, microphthalmia and shortened beaks. However, no abnormalit ies were noted i n geese and g u l l s with dosages 50 times greater and ducks dosed 250 7 times greater than the chickens. Thus, avian species can have v a s t l y d i f f e r e n t tolerances to environmental contamination. The F a i l u r e of Heron Colonies The f a i l u r e of heron colonies i n any one breeding season i s common and i s not i n i t s e l f cause for alarm. Parker (1980) studied 22 Great Blue Heron colonies i n northwestern Montana. She reported abandonments and re loca t ions of a l l or port ions of 11 co lonies i n a 10 year p e r i o d . Parker impl icated recrea t iona l or logging a c t i v i t y , as being the cause of disturbance i n a l l 11 cases. Simpson (1984) reported p a r t i a l or complete abandonment at f i v e out of 15 heron colonies on the east s ide of the S t r a i t of Georgia i n 1978 and 1979. At two of these co lonies the forests adjacent to the colony had been logged j u s t p r i o r to abandonment. At four co lonies , Bald Eagle incurs ions were e i t h e r observed by Simpson or reported by l o c a l res idents . In the case of the Crofton herons however, colony f a i l u r e co inc ided with a sudden increase i n PCDD and PCDF contamination, prov id ing the stimulus for t h i s study. 8 Hypotheses and pred ic t ions My g o a l was t o determine i f PCDD and PCDF contamination causes abnormal n e s t i n g behaviour, l e a d i n g t o n e s t f a i l u r e and abandonment i n Great Blue Herons. I proposed two hypotheses: 1) There i s a n e g a t i v e r e l a t i o n s h i p between a d u l t herons a t t e n t i v e n e s s t o t h e i r eggs and c h i c k s , and PCDD/PCDF l e v e l s found i n t h e i r eggs; and 2) There i s a p o s i t i v e r e l a t i o n s h i p between the number of f l e d g e d c h i c k s a t heron c o l o n i e s and nest behaviour o f a d u l t herons. From h y p o t h e s i s 1, I p r e d i c t e d : 1) C r o f t o n herons (high contaminant l e v e l ) s hould be l e s s a t t e n t i v e t o t h e i r n e s t s than Sidney I s l a n d herons (low contaminant l e v e l s ) ; and t h a t 2) C r o f t o n herons w i l l be d i s t u r b e d more e a s i l y than herons a t l e s s contaminated c o l o n i e s ; Hypothesis 2 l e d t o a t h i r d p r e d i c t i o n : 3) C r o f t o n herons w i l l l o s e more eggs and c h i c k s t o p r e d a t o r s than herons a t l e s s contaminated c o l o n i e s w i t h s i m i l a r p r e d a t i o n p r e s s u r e . 9 METHODS Study Species and i t s Biology Great Blue Herons are widely d i s t r i b u t e d i n North America (Palmer 1978). I s tudied the subspecies A. h. fannini, found i n coas ta l Washington State , B r i t i s h Columbia and southwestern Alaska (Palmer 1978). This subspecies has been used as a biomonitor of chemical contaminants i n the S t r a i t of Georgia s ince 1977 (Whitehead 1989). These herons are res idents and near the top of the food chain . Great Blue Herons eat invertebrates , amphibians, r e p t i l e s , f i s h , small mammals and b i r d s (Kushlan 1978). Herons i n the S t r a i t of Georgia feed on t i d a l estuarine mudflats and eelgrass (Zosterea marina) beds, moving in land during adverse weather. They consume a v a r i e t y of invertebrates , small f i s h and small mammals (see review by Verbeek and But ler 1989). Most Great Blue Herons nest i n co lon ies . P . E . Whitehead (pers. comm.) surveyed 22 heron colonies on the west s ide the S t r a i t of Georgia i n 1988. While some herons nested s i n g l y , most were i n colonies ranging up to 162 nests . 10 Herons i n coastal B.C. b u i l d t h e i r nests i n the canopy of deciduous and coniferous trees (Simpson 1984). The Great Blue Herons of the S t r a i t of Georgia begin t h e i r breeding season i n mid-March (Paine 1972, Butler 1989). The males return to the colonies f i r s t , followed one to two weeks l a t e r by the females (R.W. Butler, pers. comm.). Courtship and nest rep a i r / r e b u i l d i n g l a s t s between one and two weeks. By mid-April the f i r s t of three to s i x eggs are l a i d (Butler 1989; pers. obs.). The most l i k e l y i n t e r v a l between egg laying i s two days (Vermeer 1969, Pratt 1970). Incubation l a s t s between 25 and 29 days, (Vermeer 1969, Pratt 1970). Heron eggs hatch asynchronously, with the in t e r v a l between f i r s t and l a s t eggs hatched being between f i v e and eight days (Pratt 1970). Both males and females incubate eggs and feed the young. At lea s t one of the p a i r remains at the nest u n t i l the chicks are three to four weeks old (pers. obs.). Heron chicks leave the nest between seven and ten weeks a f t e r hatching. Study s i t e s Great Blue Herons were observed at breeding colonies at Crofton, Hammond Bay, Holden Lake, and on Sidney Island (Figures 1 and 2). These colonies were chosen on the basis of known l e v e l s of PCDD and PCDF contamination, Figure 1. Location of Great Blue Heron breeding colonies studied. 12 F i g u r e 2. L o c a t i o n s o f G r e a t B l u e Heron b r e e d i n g c o l o n i e s a t each s tudy s i t e . 13 o b s e r v a b i l i t y , s i z e , and a v a i l a b l e records on t h e i r breeding h i s t o r y . The Crofton heron colony had 60 ac t ive nests i n 1987 (Butler 1989) and was located on a small i s l a n d , c a l l e d Shoal I s land , at the end of a causeway about 300 m from a dry land log sort and 1 km from a k r a f t pulp m i l l . The herons nested i n Arbutus (Arbutus menziesii), Douglas F i r (Pseudotsuga menziesii), Garry Oak (Quercus garryana), and Western Hemlock (Tsuga heterophylla). Observations at Crofton were made from a b l i n d atop a 7 m high tower (nest height) about 35 m from the nearest nest . The heron colony on Sidney Is land had 85 ac t ive nests i n 1987 (Butler 1989) and was located i n Red Alders (Alnus rubra) w i th in the Sidney Sp i t P r o v i n c i a l Park. There i s no major i n d u s t r i a l a c t i v i t y wi th in 15 km. Observations were made from a b l i n d on the forest f l o o r 15-30 m from the nests . Both the Crofton and Sidney Is land Colonies were with in 1 km of large areas of t i d a l mudflats and eelgrass beds where most herons fed. The heron nests at Hammond Bay and Holden lake were located i n both Red Alder and Douglas F i r . Observations were 14 made from the forest f l o o r 15-30 m from the heron nests . At Holden Lake observations were a lso made from a h i l l s i d e at nest l e v e l about 200 m from the nests . The Holden Lake colony (approximately 100 nests) i s located 3.5 km south of the Harmac (kraft) pulp m i l l , Hammond Bay (approximately 20 nests) i s 15 km to the north-west of the m i l l . The p r i n c i p a l foraging areas of the Hammond Bay and Holden Lake herons are not v i s i b l e from these co lon ie s . P . E . Whitehead (pers. comm.) attempted to determine feeding areas by not ing the f l i g h t d i r e c t i o n s of herons a r r i v i n g and depart ing the co lon ies . The Hammond Bay herons appeared to feed along rocky shores and i n shallow sandy bays north and south of the colony. Holden Lake herons fed at the lake , i n the Nanaimo River estuary adjacent to the Harmac pulp m i l l , and along the rocky shores of several nearby i s l a n d s . Experimental design I compared nest behaviour and reproduct ive success of Great Blue Herons at d i f f e r e n t co lon ies , with chemical contaminant l eve l s i n t h e i r eggs. Concurrently I observed and recorded the response of herons to human a c t i v i t y , predators and any other obvious phenomena l i k e l y to a f fec t heron behaviour and breeding success. 15 Observation protocol Herons were observed at Crofton and on Sidney Is land from February through J u l y i n 1988 and i n 1989, and at Hammond Bay and Holden Lake from May through J u l y i n 1989. I measured the herons' attentiveness to t h e i r eggs and chicks at Crofton and on Sidney Is land by scor ing nest attendance and the percent of time herons spent incubat ing . Nest attendance was defined as the presence of an adult heron incubating or standing on or d i r e c t l y adjacent to i t s nest . By noting the a r r i v a l s and departures of herons from a l l nests under observation, I had a record of the proport ion of time during each three hour per iod when an adult was present at i t s nest . This gave a measure of nest attendance. At the same time, I scored the numbers of herons incubat ing , by scan samples (Altmann 1974) of the e n t i r e study group every 10 min. I considered an adult heron to be incubat ing eggs i f i t sat down r i g h t i n the centre of i t s nest . The percent time of incubation for each nest i s expressed as the proport ion of scans when a heron was incubat ing over the t o t a l number of scans for that nest . The study group consisted of a l l nests v i s i b l e from the locat ions of the b l i n d s . 16 In 1988 I observed nest ing herons one day each week from 0600 to 2000 hours P a c i f i c Dayl ight Time (PDT). No s i g n i f i c a n t changes i n the percent time incubating occurred across the day or due to t ides (P<0.05), so i n 1989 I sampled from 0600 to 0900 hours PDT with spot samples at other times. I chose 0600 to 0900 hours because of l o g i s t i c a l convenience, and because i t was the time of day with l eas t disturbances by human a c t i v i t i e s around the colony. In addi t ion to d i r e c t observations, i n 1989 I set up two JVC Super GFS550 video cameras, one at Crofton and the other a l t e r n a t i n g weekly between Hammond Bay and Holden Lake. The cameras recorded a view of the whole colony. E l e c t r o n i c timers (Commercial E l e c t r o n i c s , Vancouver) turned the cameras on to record for 30 s each 4 min. At Crofton, the t imer was adjusted each week to turn on near dawn, to record throughout the day and then shut o f f near dusk. The camera and timer were set to run each day while I was not present. By recording at a rate of 30 s i n each 4 min, a standard 2-h VHS video cassette was used each day of tap ing . At Hammond Bay and Holden Lake, tapes were changed twice each week. The cameras were set to run for 3 h each morning and for two 1 h periods each afternoon, when the sun was not fac ing the camera lens . 17 The primary purpose of the cameras was to record events leading up to a colony abandonment should i t occur. I estimated that any disturbance great enough to cause colony abandonment should be longer than 4 min. (pers. o b s . ) . A secondary purpose of the camera was to record ra tes , durat ion and causes of minor disturbance at the heron co lon ie s . Production of young i n the heron colonies at Hammond Bay and Holden Lake (1988 - 1990) was ca l cu la ted from data c o l l e c t e d by CWS b i o l o g i s t s P . E . Whitehead and A . M . Breau l t . Egg analysis C o l l e c t i o n of eggs for PCDD and PCDF ana lys i s was c a r r i e d out by a profess iona l tree cl imber under the superv i s ion of P . E . Whitehead. Two eggs were c o l l e c t e d from each c l u t c h sampled, one egg for contaminant a n a l y s i s , the other for a study on embryonic development (Bellward et al. 1990; Hart et al. i n pres s ) . Eggs for contaminant ana lys i s were transported to a nearby r e f r i g e r a t o r , cooled and held for transport to the Nat ional W i l d l i f e Research Centre i n H u l l , Quebec. Techniques for contaminant ana lys i s of these eggs can be found i n Norstrom et al. (1986). 18 I received egg analys i s data d i r e c t l y from CWS ( R . J . Norstrom or P . E . Whitehead), some of these data have been publ ished i n E l l i o t t et al. (1989) and Bellward et al. (1990). For the unpublished PCDD values , I c a l c u l a t e d TCDD t o x i c equivalents (TEQs) by m u l t i p l y i n g the ac tua l PCDD and PCDF concentrations by the t o x i c equivalence fac tors (TEFs) used by E l l i o t t et al. (1989). Data analysis Nesting Behaviour - I compared nest attendance and percent of time incubating at Crofton and Sidney Is land i n 1989 with values from 1988. To standardize incubation periods among nests i n each colony and between colonies i n the two years , I used the hatching date of the f i r s t ch ick i n the study group as a reference po in t . Hatching dates were estimated by the f i r s t c a l l s of a chick and/or the f ind ing of an egg s h e l l beneath a nest . The date that the f i r s t egg was l a i d was estimated by backdating, assuming a 28 d incubat ion p e r i o d . I compared TEQ l eve l s i n f i ve eggs, c o l l e c t e d from f ive nests at Crofton i n 1989, with the percent of time adult herons spent incubating i n those same nests . 19 Scores of the percent time of incubation d i d not f i t a normal d i s t r i b u t i o n curve and were of unequal variance ( B a r t l e t t ' s t e s t P< 0.001). For s t a t i s t i c a l comparison, I compared Rank Sums, using nonparametric K r u s k a l - W a l l i s one-way ana lys i s of variance (Wilkinson 1988). For comparison of incubat ion behaviour and TEQs at Crofton i n 1989, I c a l c u l a t e d a Pearson's c o r r e l a t i o n . Response to disturbance - I c l a s s i f i e d heron responses to Bald Eagles into f i ve categories , represent ing sequent ia l responses to p o t e n t i a l l y increas ing threat . In increas ing order , I scored: 1) NO RESPONSE: herons made no apparent behavioral changes i n response to p o t e n t i a l l y d i s turb ing s t i m u l i . 2) SUDDEN SILENCE: sudden cessat ion of voca l and behavioral a c t i v i t y i n the colony, often accompanied by herons r a i s i n g t h e i r heads and necks but continuing to incubate. 3) CHORTLE: a low nasal c l u c g h . . . . c l u c g h . . . . , described as go-go-go by C o t t r i l l e and C o t t r i l l e (1958) and Bayer (1984). During t h i s v o c a l i z a t i o n , herons e i ther remained incubating or stood up i n t h e i r nests . 4) ROAR: a loud roar ing c a l l often given by most herons i n the colony. Herons on nests would stay i n place but those perched i n the trees would usua l ly f l u s h . Bayer (1984) termed t h i s an "Awk" c a l l , composed of chort l e s repeated so r a p i d l y they merge into a s ing le sound. 20 5) FLUSH: large numbers of herons leaving t h e i r nests and f l y i n g e i t h e r to nearby tree tops or i n short c i r c l e s before re turning to nest . For s t a t i s t i c a l comparison (by ch i - square ) , I pooled the c l a s s i f i c a t i o n s of: SUDDEN SILENCE; CHORTLE; and ROAR, in to one broader category. I f the herons reacted to a stimulus by d i s p l a y i n g SUDDEN SILENCE or a more severe response, I considered that the colony was d i s turbed . I compared the types and frequencies of response to disturbance from: (i) human a c t i v i t i e s ; ( i i ) the presence of one or more eagles near the colony (defined as an eagle wi th in my f i e l d of view from the tower or b l i n d , and within approximately 50 m of the co lony); ( i i i ) Heron - Eagle in terac t ions (defined as an eagle f l y i n g into the heron colony and e l i c i t i n g a behavioral response from the herons). At Crofton and Sidney I s land , I a l so ca l cu la ted the r a t i o s between t o t a l disturbance and disturbances caused by eagles . Due to the small sample s izes (rare occurrences) from Hammond Bay and Holden Lake, these data were not compared s t a t i s t i c a l l y . Frequency of predation and disturbance - I viewed 14,744 -30 s segments of video tape, and scored p o t e n t i a l or actual disturbances to the heron colonies by e i t h e r seeing or hearing a d i s t u r b i n g st imulus. I recorded: heron disturbances , loud trucks or low f l y i n g a i rp lanes , heron -eagle in terac t ions and the presence of eagles, crows and ravens at the co lon ies . I d iv ided the nest ing stage of the colony into f i ve two-week per iods . The f i n a l two weeks of incubat ion and, 0-2, 2-4, 4-6 and 6-8 weeks post hatch. The frequency of presence, of eagles, crows, and ravens, are expressed as the number of segments of tape where the predator was heard or seen over the t o t a l number of segments screened. I used mul t ip le pairwise chi -square t es t s (1 df) to t e s t the n u l l hypothesis that the frequency of occurrences was the same i n the f i ve per iods . I der ived the expected values by d i v i d i n g the t o t a l observations of eagles, crows and ravens, by the t o t a l number of f i l m segments, then m u l t i p l i e d by the ac tua l number of segments for each time p e r i o d . To t e s t the co-occurrence of crows and eagles, I used a 2 x 2 chi-square contingency t a b l e . 22 RESULTS Reproductive Success In the past f i ve years , the Crofton and Sidney Is land heron colonies each have had three successful years and two f a i l u r e s (Table 1). When looking for l i n k s between colony f a i l u r e and environmental contamination, a l l events preceding both successful and f a i l e d nest ing attempts become important. In t h i s sect ion I report a chronology of key events at the four heron colonies studied i n 1988 and 1989. Later , i n a sect ion on disturbance and predat ion I w i l l present a d d i t i o n a l information. Crofton - In 1988, herons at the Crofton colony made four nest ing attempts (Table 1). Between 10-15 March, construct ion workers b u i l t the heron observation tower on Shoal I s land . In the l a s t two weeks of March, herons returned each evening to roost on several small i s lands near the Shoal Is land colony. On 30 March, I f i r s t not iced droppings beneath nests on Shoal I s land. I considered t h i s as t h e i r f i r s t nest ing attempt. On 31 March, I observed herons f l y i n g from feeding grounds near Shoal Is land to a point on the east shore of S a l t s p r i n g Is land (a 4-km Table 1. Production of young herons at Crofton, Hammond Bay, Holden Lake and Sidney Island colonies form 1986 to 1990. Colony Year # Active % Nests # Fledged per Reference nests/attempt successful successful nest Crofton 86 87 88 89 90 64 60 19,35,15 25 32 ND 1 0 0 84 ND 2.0 0 0 2.6 2.9 2 Butler 1989 Butler 1989 This study This study Breault pers. comm w Hammond Bay 88 89 22 13 59 62 1.6 2.0 CO Whitehead pers. comm. Whitehead pers. comm. Holden Lake 88 89 100 162 93 94 1.8 2.4 3 3 Whitehead pers. comm. Whitehead pers. comm. Sidney Island 86 87 88 89 90 75 85 99 89,43 27 ND 54 77 0 0 2.2 2.3 2.3 0 0 Butler pers. comm. Butler 1989 This study This study Butler pers.comm. 1. not documented 2. sample size = 13 3. sample size, 44 i n 1988, 35 i n 1989 di s tance ) . I considered t h i s t h e i r second nest ing attempt. On 13 A p r i l a t h i r d colony s i t e was located near Arthur Street i n the town of Crofton. At t h i s time herons were not observed to f l y towards S a l t s p r i n g , but would gather on Shoal Is land before f l y i n g the 2-km distance to Arthur S tree t . On 15 A p r i l , tree cl imbers c o l l e c t e d eggs from the Arthur Street colony. The colony was abandoned between 23-26 A p r i l ( P . E . Whitehead, pers . comm.). Between 3-11 May, herons returned to Shoal I s land, made a fourth nest ing attempt and l a i d eggs. On 8 June the f i r s t ch ick hatched. On 18 June, the colony was p a r t i a l l y abandoned, and by 28 June, the e n t i r e colony was abandoned. During the i n i t i a l heron a c t i v i t y around Shoal I s land, no egg l a y i n g was evident . However, I do consider these n i g h t l y congregations near and i n the colony as an attempt to nest . Since no eggs were l a i d , no data from t h i s attempt appears i n Table 1. Following the second attempt, on S a l t s p r i n g I s land , P. E . Whitehead (pers. comm.) located fragments of egg s h e l l beneath 19 ac t ive nests . The colony appeared to have been abandoned before c lutches were complete. The t h i r d attempt, near Arthur Street had 38 ac t ive nests . At the time of egg c o l l e c t i o n 17 nests contained eggs, nine of the 17 nests had a s ing l e egg suggesting c lutches were incomplete (A.M. Breaul t , pers . comm.). The f i n a l attempt, back at Shoal I s land , involved 15 act ive nests . I examined egg s h e l l s c o l l e c t e d beneath the colony, 12 of the 3 0 eggs c o l l e c t e d had hatched. Of the remaining eggs: 8 had been punctured and contained yolk m a t e r i a l ; 10 were too badly damaged to ass ign a fa te . In 1989, herons were f i r s t observed i n the colony on Shoal Is land on 26 March. Herons appeared to be incubating by 13 A p r i l . On 11 May tree cl imbers c o l l e c t e d eggs. The f i r s t chicks hatched on 13 May. In t h i s year, 21 out of 25 nests were success fu l , and produced an average of 2.6 young per successful nest (Table 1). In 1989, there was no heron a c t i v i t y at the Arthur Street or S a l t s p r i n g Is land colony s i t e s ( P . E . Whitehead, pers . comm.). Sidney Island - In 1988, droppings were f i r s t seen below heron nests on 17 March. By 19 A p r i l , herons were incubat ing . On 10 May the f i r s t chicks were heard. On 11 May tree cl imbers c o l l e c t e d eggs from four nests . In a l l , 76 out of 99 ac t ive nests were success fu l , with an average of 2.3 young per successful nest (Table 1). In 1989, herons were f i r s t observed i n the colony on 30 March. By 17 A p r i l herons were incubat ing . On 15 May the f i r s t chicks were heard. On t h i s same day, at 1620 hours PDT, R.W. But ler and I heard loud roars from the heron colony and observed many herons c i r c l i n g overhead. On 26 enter ing the forest we found a Bald Eagle beneath the colony-consuming an adult male heron. As we approached at 1624 hours, the eagle departed. By 1626 hours herons began to re turn to the colony and a l l was quiet by 1629 hours. On 22 May, I found a l l 66 ac t ive nests abandoned. Crows and ravens were c a l l i n g and f l y i n g about the colony. I c o l l e c t e d 162 broken egg s h e l l s from the forest f l o o r wi th in 150 m of the colony, 49 of which had a large puncture at i t s equator and contained remnants of yo lk . Later t h i s same day, two people on b i c y c l e s rode "hooting and h o l l e r i n g " through the heron colony. The next day, 23 May, several p a i r s of herons were on nests i n the colony. On 5 June I counted 43 ac t ive nests i n t h i s new breeding attempt. On 12 June the colony was again abandoned, no herons were observed on Sidney Is land on 13 June. Hammond Bay and Holden Lake - These heron colonies were successful i n both 1988 and 1989 (Table 1) . At Hammond Bay, 13 out of 22 nests were successful i n 1988, and 8 out of 13 nests i n 1989. At Holden Lake there were 100 ac t ive nests i n 1988; 41 of the 44 nests surveyed were success fu l . In 1989 there were 162 ac t ive nests , and 33 out of the 35 surveyed were success fu l . 27 Nest Attentiveness and PCDD Contamination In t h i s sec t ion I c o r r e l a t e the behaviour of both male and female adult herons with tox in l e v e l s found i n t h e i r eggs. PCDD contamination - PCDD and PCDF l e v e l s i n heron eggs from Crofton dropped from 1987 to 1989 (Figure 3) . The l e v e l s recorded i n 1989 were not s i g n i f i c a n t l y d i f f e r e n t from those i n 1986, the l a s t year the colony was success fu l . However, the 1989 l e v e l was s t i l l f i ve times as high as that at the Sidney Is land colony, s i tuated far from the nearest m i l l . Nest attendance - Nest attendance at Crofton and Sidney Is land was between 95 and 100 % at 52 nests sampled during the incubat ion per iod i n 1988 and 1989 (Table 2) . Incubation behaviour - The mean percent times of incubation at Crofton i n 1988 and 1989, and on Sidney Is land i n 1988 were not s i g n i f i c a n t l y d i f f e r e n t (Kruskal -Wal l i s chi -square approximation)(Figure 4) . Of greatest i n t e r e s t i s how the amounts of time herons incubated at i n d i v i d u a l nests were s i g n i f i c a n t l y more v a r i a b l e ( B a r t l e t t ' s t e s t P<0.001) at Crofton i n 1988, a year of both elevated PCDD l e v e l s (Figure 3) and f a i l u r e of breeding attempts. 28 500 r .? 400 5 300 O) v. O) c I 200 a> O a o 100 a. i 2 3 7 8 - T C D 0 0 T C D D e q u i v a l e n t s 1986 1987 1988 Crofton 1989 1986 1988 Sidney Island Figure 3. Levels of 2378 TCDD and TCDD t o x i c equivalents i n Great Blue Heron eggs c o l l e c t e d at Crofton (1986 and 1987 N=10, 1988 N=7, 1989 N=5) and on Sidney Island (1986 N=4, 1988 N=5 pooled). Horizontal l i n e s indicate the geometric mean, boxes depict the 95% confidence i n t e r v a l , and v e r t i c a l l i n e s indicate the range. Table 2. Nest attendance during the incubation per iod at the Crofton and Sidney Is land heron co lonies . hours attendance N 1 colony year hours observation X SD Crofton 1988 50 47.6 5.4 8 1989 35 34.5 1.5 16 Sidney Island 1988 68 68.0 0 14 1989 21 21.0 0 14 1. number of nests observed 30 c cu E 100 80 ro n =} o c 60 40 - E 3 -- E 3 -c cu o v-a 20 1988 1989 Crofton 1988 1989 Sidney Island Figure 4. Percent of time Great Blue Herons spent incubating at Crofton (1988:N=8; 1989:N=16) and on Sidney Island (1988 & 1989:N=14). Horizontal l i n e s indicate the mean, boxes depict the 95% confidence i n t e r v a l , and v e r t i c a l l i n e s indicate the range. In 1989, eggs were c o l l e c t e d at Crofton from f i v e nests that were observed. The percent time herons incubated at these nests were p lo t t ed against l e v e l s of TEQs (Figure 5) . The ac tua l TEQ l e v e l s were a lso compared with c l u t c h s i z e and numbers of successful f l edg l ings (Table 3) . There was no s i g n i f i c a n t c o r r e l a t i o n between TEQ l e v e l s and percent time spent incubating or with reproductive success. However, i t should be pointed out that the non-s igni f icance could be due to a small sample of only f i ve data po in t s . In summary, these data suggest a p o s i t i v e r e l a t i o n s h i p between PCDD/PCDF l eve l s and both colony f a i l u r e and v a r i a t i o n i n incubation behaviour at Crof ton . Disturbance and Fredation Human activities near the heron colonies - Herons nest ing at both Crofton and on Sidney Is land were d is turbed by human a c t i v i t i e s as described above. A l s o , At Crofton i n 1988, I often saw foo tpr in t s on the beach near the heron colony. Aside from one m i l l employee walking during h i s lunch break, and a l o c a l reporter intercepted on h i s way in to the colony (A.M. Breaul t , pers . comm.), the o r i g i n s of these footpr int s and the intent ions of those making them were not determined. In 1989, m i l l s t a f f and the l o c a l media were informed of the video camera monitoring the colony. In 1989 I found no 32 100 c 13 80 CO n O c CD E 60 + 1 + 40 c cu o £ 20 a 50 100 150 200 250 TCDD toxic equivalents (ng/kg) 300 Figure 5. Percent of time Great Blue Herons i n f i v e nests at Crofton i n 1989, spent incubating, compared to TCDD to x i c equivalent l e v e l s i n a sample of t h e i r eggs. Horizontal l i n e s indicate the mean, v e r t i c a l l i n e s depict one standard deviation. Table 3. Production of eggs and young, i n f ive heron nests at Crofton i n 1989, compared with l eve l s of 2 ,3 ,7 ,8 TCDD and TCDD t o x i c equivalents found i n t h e i r eggs. # eggs # eggs # eggs # chicks PCDD l e v e l (ng/kg) nest in removed that fledged c lutch hatched TCDD TEQs 3 5 2 3 2 255 291 4 5 2 2 2 93 109 5 5 2 3 3 117 138 7 5 2 3 2 30 34 11 6 1 4 1 3 34 40 1. I d i d not observe a f i f t h ch ick , presumably the f i n a l egg d id not hatch or the ch ick was k i l l e d before i t was large enough for me to see i t 34 evidence of unexplained human a c t i v i t i e s i n or near the colony. The Sidney Is land colony i s located i n the fores t about a 30 min from the centre of human a c t i v i t i e s i n the p r o v i n c i a l park (Figure 2) . In terms of o v e r a l l v i s i t o r s to the park, very few reach the colony. Each year as the weather warms, the park receives more and more v i s i t o r s , e s p e c i a l l y on the weekends. In l a t e A p r i l and ear ly May v i s i t o r s a r r i v e by pr iva te boat. In ear ly May, the park wharf i s i n s t a l l e d , increas ing access to the park. In mid-May, passenger f e r r y serv ice begins. In 1989, a new park boundary fence funnel led park v i s i t o r towards the colony. Although actua l counts of v i s i t o r s were not made, they appeared to have increased i n 1989. Human a c t i v i t i e s at or near the heron colony increased through the season. Not a l l human a c t i v i t i e s e l i c i t e d a response from the herons. For example, on 30 May 1989 between 1330 and 1420 hours, a group of about 30 c h i l d r e n , aged 10 to 12 passed twice wi th in 10 m of the colony edge. The c h i l d r e n were y e l l i n g and screaming, and chasing each other, but the herons d i d not appear to reac t . Fol lowing the two abandonments i n 1989, I searched the fores t around the colony for any evidence ( f i r e p i t s , beer b o t t l e s , broken 35 trees) that could l i n k human a c t i v i t i e s to the colony-abandonment, but found nothing. The heron colonies at Hammond Bay and Holden Lake are on p r i v a t e property . The land owners are very pro tec t ive of "their" herons. There was no evidence of d i s t u r b i n g human a c t i v i t i e s i n e i t h e r of the study years . Disturbance and predation by eagles - Bald Eagles were observed r e g u l a r l y throughout the breeding season at both the Crofton and Sidney Is land heron colonies (Table 4) . In 1989, the year Crofton was success fu l , o v e r a l l eagle s i gh t ing at the colony were double that of 1988, the year the colony f a i l e d (Chi-square P< 0.01)(Tables 4 and 5) . During t h i s same time, eagle incurs ions at Crofton increased by almost four-t imes (P< 0.05)(Table 5) . There were no s i g n i f i c a n t changes i n eagle a c t i v i t y or incurs ions at the Sidney Is land colony over the two years of t h i s study. At Crofton i n 1988 eagles were s ighted at the colony s i g n i f i c a n t l y more often (P< 0.05) i n June, the time of the f i n a l abandonment, compared to the res t of the nest ing season. At Crofton i n 1989, there were s i g n i f i c a n t l y (P< 0.05) fewer eagle s ight ings i n March than expected (that the frequency of eagle s ight ings would be equal from March to Table 4. Frequency of Bald Eagle s ightings at the Crofton and Sidney Is land heron co lon ies , March through Ju ly 1988 and 1989. Crofton Sidney Island Month 1988 Obs.\Exp. 1989 Obs . \Exp. 1988 Obs . \Exp. 1989 Obs. \Exp. March 2\5.3 (46h)1 0\6.5 (23h) 0\0.5 (4h) 0\2. 6 (26h) A p r i l 1\1.7 (15h) 41\20. 5 ** (72h) 5\5.4 (42h) 4\3. 9 (40h) May 2\3.6 (32h) 32\39. 6 (139h) 7\9.7 (75h) 9\5. 9 (60h) June 11\5.4 * (7h) 36\34. 3 (120.5h) 11\10.3 (80h) 4\4. 6 (47h) J u l y NA2 20\28. 0 (98.5h) 11\8.1 (63h) NA T o t a l 16 (140h) 129 (453h) 34 (264h) 17 (173h) * P <0.05 ** P <0.01 1. hours of observation 2. colony abandoned 37 Table 5. Frequencies of Heron - Eagle interactions and eagle presence at Great Blue Heron colonies. Frequencies / h of observation hours colony year of H - E 1 eagles observation interactions present Crofton 1988 140 0.04 0.11 1989 456 0.16 0.28 Hammond Bay 1989 78 0.01 0.10 Holden Lake 1989 79 0 0.10 Sidney Island 1988 270 0. 09 0.13 1989 186 0.05 0.10 Overall 1209 0.09 0.17 1. Sum of silence, Chortle, roar, and fl u s h responses (see Table 6). 38 J u l y ) . In A p r i l , eagle a c t i v i t y near the colony increased to nearly twice expected l eve l s (P< 0.01) given the same c r i t e r i a . Eagle s ight ings at the Sidney Is land colony were very constant i n both 1988 and 1989. Comparing the types and frequencies of responses to Bald Eagles , there were 2.8 times (P< 0.01) more eagle s ight ings per hour of observation (Table 4) , and three times (P<0.01) more Heron - Eagle in terac t ions at Crofton than on Sidney Is land i n 1989 (Table 5) . According to my c r i t e r i a there was no s i g n i f i c a n t d i f ference (P> 0.05) i n sever i ty of response to eagles at Crofton i n 1988, compared to 1989, or to Sidney Is land i n e i ther year (Table 6) . During the successful year of 1989, herons at Crofton f lushed 3.3 times more often (P< 0.05) than herons on Sidney Is land i n 1989, the year Sidney f a i l e d . In contrast , herons on Sidney Is land f lushed 5.8 times more often (P< 0.01) during the f a i l u r e year of 1989 when compared to 1988. In 1989, Bald Eagles were observed at Hammond Bay and Holden Lake though no predation events were witnessed. Stan Thomas, the land owner at Hammond Bay, reported "frequent" eagle incurs ions into the heron colony. Bald Eagles were nest ing approximately 300 m from the heron colony. At Holden Lake on s i x occasions herons were observed to f lush from Table 6. Responses of herons to the presence of eagles near the Crofton and Sidney Is land heron co lonies . Hours Response to eagle presence colony year of t o t a l observation none s i l ence chort l e roar f lush Crofton 1988 140 11 1 0 3 1 16 1989 456 58 12 3 28 28 129 Sidney Island 1988 270 9 9 4 9 3 34 1989 186 8 0 1 2 7 18 O v e r a l l 1209 86 22 8 42 39 197 40 t h e i r nests or to stand up and make alarm c a l l s as a Red-t a i l e d Hawk (Buteo jamaicensis) flew overhead. Predation by crows and ravens - Casual observations i n 1988 suggested that crows f l y to the heron colonies when eagles a r r i v e . In 1989 at Crofton, I found the observed co-occurrence of crows and eagles to be three times the expected occurrences (P< 0.01) given chance alone (Table 7) . I f crows and ravens represent a s i g n i f i c a n t threat to heron eggs and nes t l ings , t h e i r occurrence at the co lonies should be most frequent i n the egg and ear ly n e s t l i n g stages. Beyond t h i s stage, the s i z e , weight, and defensive a b i l i t y of the growing heron chicks would prevent crows and ravens from ca rry ing them of f . Examination of video tape recorded at Crofton i n 1989 supports t h i s p r e d i c t i o n . Compared to my expectat ion, crow s ight ings would be equal ly frequent i n a l l stages of the nest ing per iod , there were s i g n i f i c a n t l y (chi-square P< 0.01) fewer s ight ings i n the egg stage (Table 8) , and twice as many s ight ings (P<0.01) during l a t e incubat ion , and the f i r s t three weeks post hatch. Ravens were observed at the heron colony most often during the egg (P< 0.01) and hatching stages. Once heron chicks reached 2-4 weeks of age, ravens were seldom observed at the colony. 41 Table 7. Frequency of crow and eagle occurrences at the Crofton heron colony i n 1989 Number of tape segments Observed Expected Crows alone 448 467.3 Crows with eagles 29 9.7 Eagles alone 239 258. 3 No crows or eagles 12,440 12,420.7 Total # of tape segments 13,156 X2 = 38.5, d.f.= 1 42 Table 8. Frequency of crow and raven sightings at the Crofton heron colony during incubation (30 A p r i l - 13 May) and chick stages (14 May - 8 July) i n 1989. Bold type face indicates more sightings than expected. Nesting stage Crows Obs.\Exp. P Ravens Obs.\Exp. P Total # tape segments Egg 47\107.1 <0. 01 23\8.3 <0.01 2953 Chick < 2 weeks 152\100.2 <0.01 12\7.8 NS 1763 2 - 4 weeks 183\95.7 <0.01 1\7.4 <0.01 2639 4 - 6 weeks 53\89.2 <0.01 0\6.9 <0.01 2461 6 - 8 weeks 42\84.8 <0.01 1\6.6 <0.01 2338 Total 477 37 13,119 43 I d i d not observe ravens at the Hammond Bay and Holden Lake co lon ie s . Crow s ight ings at these two colonies was very low (three out of 1,618 f i l m segments with c a l l s ) . DISCUSSION During t h i s study, the Crofton heron colony f a i l e d i n 1988 and was successful i n 1989, the reverse was true for the Sidney Island colony. Of p a r t i c u l a r i n t e r e s t i s whether the f a i l u r e at Crofton could be linked to environmental contamination. I w i l l f i r s t discuss evidence supporting and opposing my hypotheses l i n k i n g heron behaviour and colony f a i l u r e , with PCDD and PCDF contamination. I then discuss heron colony f a i l u r e i n general, by looking at human disturbance and predation. Reproductive F a i l u r e and PCDD\PCDF Contamination Supporting evidence - There are two pieces of evidence that l i n k the Crofton f a i l u r e to PCDD and PCDF contamination: (1) During the two years (1987 and 1988) when PCDD l e v e l s were high, the colony f a i l e d (Table 1 & Figure 3); and (2) during the two study years, (1988 and 1989), there was s i g n i f i c a n t l y higher v a r i a t i o n i n incubation frequencies (P< 0.001) when PCDD\PCDF l e v e l s were high and lower v a r i a t i o n when PCDD\PCDF l e v e l s were low (Figures 3 & 4). In both the above cases there i s a d e f i n i t e association, but causal rela t i o n s h i p cannot be assigned. However, there i s additional supportive evidence from Bellward et al. (1990) and Hart et al. (in press). These studies compared embryonic development i n a sample of 13 heron eggs c o l l e c t e d at Crofton i n 1988 with two l e s s e r contaminated colonies. A l l the Crofton eggs were f e r t i l e and 12 out of the 13 hatched i n an incubator. Bellward et al. (1990) found a s i g n i f i c a n t c o r r e l a t i o n (P< 0.001) between the induction of hepatic d e t o x i f i c a t i o n enzymes i n heron hatchlings and toxin l e v e l s i n s i b l i n g eggs. Hart et a l . (in press) report: (i) a c o r r e l a t i o n between toxins and reduced growth of bones and organs; and ( i i ) signs of subcutaneous edema i n four out of 12 heron hatchlings. Together these studies indicate that at the 1988 l e v e l s of exposure, the pair-bonding and mating behaviour were probably not affected by PCDDs and PCDFs to r e s u l t i n lowered f e r t i l i t y . Although there was abnormal embryonic development, such as reduced growth c h a r a c t e r i s t i c s and subcutaneous edema, we do not know i f these abnormalities contributed to colony abandonments. Opposing evidence - There are two pieces of evidence that suggest PCDDs and PCDFs were not the major cause of the 1988 f a i l u r e of the Crofton heron colony: (1) There was no c o r r e l a t i o n between egg TEQ l e v e l s and performance of f i v e heron nests (accepting that the extremely small sample was representative)(Table 3 & Figure 5); and (2) Heron colonies f a i l without p o t e n t i a l l y t o x i c l e v e l s of chemical contaminants. The Sidney Island colony known to have low contamination l e v e l s , f a i l e d i n 1985, 1989 and again i n 1990 (R.W. Butler, pers. comm.). In 1988, P.E. Whitehead (unpub.) observed f a i l u r e s at many heron colonies both near and f a r from i n d u s t r i a l a c t i v i t y . At most of these colonies, disturbance by human a c t i v i t i e s or predation by eagles was eithe r observed by researchers or reported by l o c a l residents. The frequencies of disturbance and predation at Crofton i n both 1988 and 1989, suggest contaminants were not s o l e l y responsible for the 1988 f a i l u r e . I w i l l discuss disturbance and predation again l a t e r . When making correlations between contaminant l e v e l s and heron behaviour there are several p o t e n t i a l sources of error. I assumed that toxin concentrations i n eggs were correlated to the contaminant burdens i n female herons as demonstrated by Vermeer and Reynolds (1980) and Mineau et al. (1984). I could f i n d no report i n the l i t e r a t u r e describing the contaminant concentrations i n avian sperm, so consider i t s contribution to contaminants i n the egg as n e g l i g i b l e . I made no e f f o r t to determine contaminant l e v e l s i n male herons. I observed heron nesting behaviour during daylight hours. Paine (1972); Brandman (1976) and R.W. Butler (pers. comm.) suggest female herons incubate more often at night. I was unable to sex herons on the nest, though I d i d observe herons exchanging at a l l hours of the day. Therefore, my data are a sample of male and female behaviours at i n d i v i d u a l nests. In summary, there were too many constraints (e.g. unmarked birds, i n a b i l i t y to sex adults from a distance, incursions into the colonies by researchers, small numbers of eggs analyzed for contaminants, due to the cost of analysis) on the c o l l e c t i o n of data to enable me to e s t a b l i s h a d e f i n i t e causal r e l a t i o n s h i p between contaminant l e v e l s and the incubation behaviour of Great Blue Herons at the Crofton colony. Colony F a i l u r e i n General Aside from environmental contaminants, the two most important factors contributing to heron colony f a i l u r e i n coastal B r i t i s h Colombia seem to be human disturbance, and predation (Simpson 1984; Forbes 1987; P.E. Whitehead pers. comm.) . 48 Human disturbance - The adverse e f f e c t s of human a c t i v i t i e s on heron colonies i s well documented (Parker 1980; Simpson 1984; Vos et al. 1985). But, human a c t i v i t i e s do not always r e s u l t i n colony abandonment. Herons are known to habituate and to breed normally under conditions of human disturbance. A colony i n Stanley Park i s located i n trees i n and around a parking l o t and Zoo heavily used by people (Simpson 1984). S i m i l a r l y , a colony near the Nicomekl River, situated over a dog kennel and horse paddock i s exposed to constant human a c t i v i t i e s (pers. obs.). The Crofton colony i s located less than 100 m from a causeway used extensively by heavy logging trucks. In a l l these instances the disturbance l e v e l i s r e l a t i v e l y constant. I suggest that sudden changes i n disturbance pattern are more detrimental to breeding herons than disturbance per se. For example, on Sidney Island, a f t e r the park boundary fence was b u i l t i n 1989, thus changing the human t r a f f i c pattern near the colony, the herons abandoned two years i n a row. The timing of disturbances i s also very important. At Crofton i n 1988, herons were disturbed repeatedly by: (i) the tower construction, ( i i ) egg c o l l e c t i o n , and ( i i i ) human a c t i v i t y i n and around the colony (as evidenced by fo o t p r i n t s ) . I do not know the extent of human a c t i v i t y at Crofton i n 1987, another year the colony f a i l e d . But i n 1989, when i t was common knowledge that a video camera was 49 recording events at the colony, disturbance by m i l l workers and other human a c t i v i t i e s were reduced to a minimum, and the colony succeeded. On Sidney Island, the absence of human a c t i v i t i e s early i n the breeding season was broken by disturbances on sunny weekends and following the onset of the f e r r y service. Predation - The occurrence of Bald Eagles at Great Blue Heron colonies has been reported by several authors (Krebs 1974; Parker 1977; Bayer 1979; K e l s a l l and Simpson 1980; Forbes 1987; Butler 1989; Norman et al. 1989). Heron remains have been found beneath eagle nests both on the west and east coasts of North America (Cash et al. 1985; Vermeer 1989). I have observed eagles preying upon heron chicks (see Norman et al. 1989), fledglings and adults. As mentioned above, Bald Eagles were observed frequently at both the Crofton and Sidney Island heron colonies. I t i s most in t e r e s t i n g that the Crofton herons, while being disturbed more frequently, would often not respond to the presence of eagles perched d i r e c t l y above and i n c l e a r view of the colony. Eagles on Sidney Island could normally be observed perched i n trees next to t h e i r nest, out of view and about 300 m from the heron colony. I suggest that the Crofton herons habituated to the presence of eagles. The greater number of reactions by the herons on 50 Sidney I s land , may be due to the surpr i se e f fec t of eagles suddenly passing over the colony. Whether or not Bald Eagles represent a s i g n i f i c a n t threat to breeding Great Blue Herons i s unknown, but i t s impl i ca t ions for the evolut ion of c o l o n i a l nest ing has been discussed by Forbes (1987, 1989). I f eagles are a threa t , I would expect the herons to nest i n locat ions d i s tan t from eagles i f pos s ib l e . But ler (1990) found no r e l a t i o n s h i p between numbers of successful nests , brood s i z e , and spacing of co lonies and eagle nests . I t would appear that s ince both herons and eagles are drawn to s i m i l a r coas ta l feeding areas, the herons must accept some eagle predat ion . Stalmaster (1987) describes Bald Eagles defending exc lus ive feeding t e r r i t o r i e s . Presumably i f a heron colony i s located wi th in such a t e r r i t o r y , the herons may rece ive protec t ion from the greater eagle populat ion i n exchange for some losses to the home p a i r of eagles. The s i g n i f i c a n c e of eagle a c t i v i t y near heron colonies l i e s i n i t s e f fec t on colony p r o d u c t i v i t y . While the loss of i n d i v i d u a l herons or nests may not s i g n i f i c a n t l y a f fec t colony p r o d u c t i v i t y , a severe response by herons to a predator could r e s u l t i n colony f a i l u r e . Heron nests abandoned even temporari ly leave eggs or chicks vulnerable to opportun i s t i c predat ion . I be l i eve that opportun i s t i c 51 predation and scavenging by crows and ravens i s a much more s i g n i f i c a n t threat to colony success than eagle predation alone. Butler (1989) observed ravens carrying heron eggs from the Sidney Island colony i n 1987 and estimated egg losses of 11.2%. The presence of both crows and ravens i n the Sidney Island colony, and the numerous punctured heron eggs i n the surrounding forest i n 1989, suggested that corvids contributed to colony f a i l u r e . In 1990 on Sidney Island, T.M. Su l l i v a n (pers. comm.) observed an immature Bald Eagle i n the heron colony. During the r e s u l t i n g disturbance, ravens quickly entered the colony and removed heron eggs. The herons, a f t e r returning to empty nests, abandoned the colony. Punctured heron eggs c o l l e c t e d from beneath the Crofton colony i n 1987 (P.E. Whitehead and R.W. 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