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Factors affecting reproduction in great blue herons (Ardea herodias) Simpson, Keith 1984

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FACTORS AFFECTING REPRODUCTION IN GREAT BLUE HERONS (Ardea  herodlas)  By KEITH SIMPSON B.Sc,  Simon F r a s e r U n i v e r s i t y , 1 9 7 ^  A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in THE FACULTY OF GRADUATE STUDIES (Department o f Zoology)  We accept  t h i s t h e s i s as conforming  to the r e q u i r e d  standard /7  THE UNIVERSITY OF BRITISH COLUMBIA September 1 9 8 ^ ©  K e i t h Simpson, 1 9 8 ^  In p r e s e n t i n g  t h i s t h e s i s i n p a r t i a l f u l f i l m e n t of  requirements f o r an advanced degree a t the  the  University  o f B r i t i s h Columbia, I agree t h a t the L i b r a r y s h a l l make it  f r e e l y a v a i l a b l e f o r reference  and  study.  I  further  agree t h a t p e r m i s s i o n f o r e x t e n s i v e copying o f t h i s t h e s i s f o r s c h o l a r l y purposes may department o r by h i s or her  be  granted by  the head o f  representatives.  my  It i s  understood t h a t copying or p u b l i c a t i o n of t h i s t h e s i s f o r f i n a n c i a l gain  s h a l l not be  allowed w i t h o u t my  permission.  Department o f  2-QO  t-06^  The  U n i v e r s i t y o f B r i t i s h Columbia  1956  Main  Mall  Vancouver, Canada V6T  1Y3  written  ii ABSTRACT Reproductive monitored  success and  from 1 9 7 7  s i z e o f 15 h e r o n r i e s were  to 1 9 8 0 i n south c o a s t a l B r i t i s h  Columbia.  My main o b j e c t i v e s were to i n v e n t o r y e x i s t i n g c o l o n i e s , assess changes i n colony s t a t u s from h i s t o r i c a l i n f o r m a t i o n , and document f a c t o r s important on banded herons a t one  to r e p r o d u c t i o n .  I collected  data  colony to d e s c r i b e the movement o f  herons between and w i t h i n h e r o n r i e s , and  to i d e n t i f y  the  c h a r a c t e r i s t i c s o f i n d i v i d u a l s t h a t r e l a t e d to r e p r o d u c t i v e success.  Many h e r o n r i e s f o r m e r l y i d e n t i f i e d were no  present w h i l e o t h e r s were a t new size.  longer  l o c a t i o n s o r much l a r g e r i n  Heronry movements f o l l o w e d d e s t r u c t i o n o f the nest  trees or reproductive l o s s e s i n s e v e r a l cases.  Relocation  normally o c c u r r e d i n the f i r s t or second year f o l l o w i n g heavy l o s s e s o f young or a d u l t s .  Disturbances by people  f o r c e d herons to l e a v e t h e i r n e s t s and eggs and young to p r e d a t o r s .  increased losses of  Severe p r e d a t i o n continued  human d i s t u r b a n c e had stopped. s u c c e s s f u l nest was  sometimes  after  The number o f young r a i s e d  per  not a u s e f u l measure o f r e p r o d u c t i v e  success, s i n c e i t v a r i e d l i t t l e among c o l o n i e s .  The  percentage  o f nests that succeeded, or numbers o f young r a i s e d per  breed-  i n g p a i r , p r o v i d e d b e t t e r measures o f r e p r o d u c t i v e s u c c e s s . Marked herons a t one  colony were not a t t a c h e d to s p e c i f i c  n e s t s or mates, and many a d u l t s p r o b a b l y switched c o l o n i e s each year.  U n s u c c e s s f u l p a i r s d i d not r e n e s t i n the same colony  d u r i n g the same b r e e d i n g season.  Although  herons i n c e n t r a l  n e s t s were more s u c c e s s f u l than those near the edge o f the  iii colony, c e n t r a l n e s t s were not occupied by b i r d s which were dominant on f e e d i n g a r e a s .  Herons a r e probably a t t r a c t e d to  c o l o n i e s to f i n d new mates each year, and to reduce the v u l n e r a b i l i t y o f t h e i r young to p r e d a t o r s .  Although  7 8 percent  o f the herons i n one colony f e d i n the n e a r e s t f e e d i n g a r e a s , many chose to t r a v e l f u r t h e r to f e e d .  These d i s t a n t  feeders  s u f f e r e d h i g h e r nest l o s s e s to p r e d a t o r s , probably because they l e f t  t h e i r nests unattended  l o c a l l y feeding b i r d s .  more o f t e n than o t h e r  Some evidence  suggested  t h a t males  t r a v e l l e d f u r t h e r than females, and were l e s s a t t e n t i v e a t the n e s t .  Males may p l a y a dominant r o l e i n i n i t i a t i n g  relocations.  The l a c k o f attachment o f herons to nest  colony sites  o r mates h e l p s to e x p l a i n the changes i n s i z e and frequent movements o f h e r o n r i e s i n c o a s t a l B.C.  iv Table o f Contents PAGE Abstract Table o f Contents L i s t o f Tables L i s t o f Figures Acknowledgements  i i iv vi viii ix  General I n t r o d u c t i o n  1  CHAPTER I — L o c a t i o n , S i z e , H i s t o r y and Reproductive Success o f H e r o n r i e s i n South C o a s t a l B.C.  3  Introduction  4  Methods  5  Results Heronry l o c a t i o n s , s i z e s and general descriptions H i s t o r i c a l and p r e s e n t colony data Reactions to human d i s t u r b a n c e Reproductive success  8 11 25 25  Discussion Colony s i z e s R e a c t i o n s to human d i s t u r b a n c e Predation Reproductive success  30 3^ 35 38  Conclusions  42  CHAPTER II—Movements, Behavior and Breeding Success o f Banded Herons a t Pender Harbour  44  Introduction  45  Methods  47  Results Capture and banding R e s i g h t i n g s and movements o f banded herons Feeding areas and n e s t i n g s t a t u s Nest s i t e s , mates and f e e d i n g areas  5  2  52 53 58  V  PAGE R e s u l t s (Cont.) Feeding on t i d a l areas Feeding a t the b a i t tanks Aggressive I n t e r a c t i o n s Sex and r e p r o d u c t i v e success  General  61 6k 64 67  Discussion Colony formation P r e d a t i o n , r e p r o d u c t i v e success and a d u l t s u r v i v a l C o l o n i a l n e s t i n g and i n f o r m a t i o n exchange Sex and r e p r o d u c t i v e success  71  Conclusions  7$  D i s c u s s i o n and Recommendations  79  68  73 75  Literature Cited  81  Appendix  86  vi L i s t o f Tables PAGE 1-1  1-2  Number o f s u c c e s s f u l nests i n heron c o l o n i e s surveyed i n south c o a s t a l B r i t i s h Columbia. Comparison o f p a s t and present  10  sizes  o f f o u r c o l o n i e s In the lower mainland.  11  1-3  D e s c r i p t i o n s o f the study c o l o n i e s .  12  1-4  S i z e and l o c a t i o n s o f the S t a n l e y Park colony from 1 9 2 1 to 1 9 8 0 . Number o f nests abandoned and newlyo c c u p i e d between survey dates a t e i g h t c o l o n i e s i n 1 9 7 8 and two i n 1 9 7 9 .  1-5  1-6  1- 7  2- 1  2-2  2-3  2-4  22 28  Mean numbers o f young f l e d g e d per succ e s s f u l nest and per breeding p a i r a t e i g h t c o l o n i e s i n 1 9 7 8 and two i n 1 9 7 9 .  29  Number and % o f nest p l a t f o r m s o c c u p i e d d u r i n g the breeding season a t e i g h t heronries.  31  Number o f s i g h t i n g s o f banded herons a t Pender Harbour from 1 9 7 8 to I 9 8 O c a t e g o r i z e d by frequency o f o b s e r v a t i o n , s i g h t i n g l o c a t i o n and presence i n the colony.  55  Comparison o f the r e p r o d u c t i v e success o f l o c a l f e e d i n g (LF) and d i s t a n t f e e d i n g (DF) herons a t Pender Harbour i n I 9 7 8 and 1 9 7 9 .  56  Comparison o f the number o f s i g h t i n g s o f d i s t a n t f e e d i n g (DF) herons to determine i f u n s u c c e s s f u l b i r d s were seen l e s s o f t e n than s u c c e s s f u l b i r d s a f t e r t h e i r young were l o s t .  57  Mean d i s t a n c e s (m) o f s u c c e s s f u l and u n s u c c e s s f u l nests from the c e n t e r o f the colony i n 1 9 7 8 and 1 9 7 9 a t Pender Harbour.  59  vii PAGE 2-5  2-6  2-7  2-8  2-9  2-10  2-11  T o t a l number o f banded herons from each s e c t o r o f the Pender Harbour colony seen f e e d i n g together on f o u r d i f f e r e n t days i n 1 9 7 9 .  59  The number o f s i g h t i n g s f o r each member o f 11 banded p a i r s a t f i v e f e e d i n g l o c a t i o n s i n Pender Harbour i n 1 9 7 9 .  60  F a c t o r s a f f e c t i n g the weight (gm) o f prey caught by herons on t i d a l f e e d i n g areas.  62  Comparison o f the weight o f prey caught by herons which s u c c e s s f u l l y r a i s e d young and those that f a i l e d to r a i s e young i n 1 9 7 9 .  64  Comparison o f the dominance o f banded herons with d i f f e r e n t r e p r o d u c t i v e success and f e e d i n g areas a t Pender Harbour i n 1 9 7 9 .  66  Comparison o f the t o t a l number o f a g g r e s s i v e i n t e r a c t i o n s f o r banded herons i n r e l a t i o n to r e p r o d u c t i v e success and f e e d i n g areas a t Pender Harbour i n 1 9 7 9 .  66  Changes i n r e p r o d u c t i v e success f o r e i g h t males and s i x females from 1 9 7 8 to 1 9 7 9 .  67  viii  L i s t o f Figures PAGE 1-1  1-2  1-3  1- 4  2- 1 2-2  2-3  Heron c o l o n y l o c a t i o n s i n t h e l o w e r m a i n l a n d and Sunshine Coast a r e a s o f B r i t i s h Columbia.  9  Mean numbers o f young f l e d g e d p e r s u c c e s s f u l n e s t a t 10 h e r o n r i e s from 1977 to 1 9 8 0 .  27  The r e l a t i o n s h i p between t h e p e r c e n t a g e of nest platforms occupied a t fledging and t h e p e r c e n t a g e o f u n s u c c e s s f u l p a i r s a t e i g h t c o l o n i e s i n 1 9 7 8 and two i n 1 9 7 9 .  32  The r e l a t i o n s h i p between t h e p e r c e n t a g e of nest platforms occupied a t f l e d g i n g and t h e p e r c e n t a g e o f u n s u c c e s s f u l p a i r s at c o l o n i e s i n Quebec and _ Montana.  4.1  Locations of traps, observation blinds and s e i n i n g s i t e s a t Pender Harbour.  48  Frequency d i s t r i b u t i o n o f t h e number o f s i g h t i n g s o f 41 l o c a l and 2 5 d i s t a n t f e e d i n g banded herons a t Pender Harbour.  54  C o r r e l a t i o n between t h e mean weight o f p r e y caught by herons (N = 9 0 7 ) and t h e mean weight caught by s e i n i n g (N = 244) f o r f i v e months i n 1 9 7 9 .  63  ix  ACKNOWLEDGEMENTS The Canadian W i l d l i f e S e r v i c e p r o v i d e d f i n a n c i a l support f o r t h i s s t u d y and I e s p e c i a l l y Dr. Don F l o o k , R i c k McKelvey  w i s h t o thank Dr. John K e l s a l l ,  and Pam Whitehead, a l l o f C.W.S.,  f o r a s s i s t a n c e and a d v i c e d u r i n g t h i s s t u d y .  Rhonda M a r k e l ,  M a r g r l e t Wyborne, S c o t t F o r b e s , B i l l Harper and Tony W i d e s k i assisted  w i t h summer f i e l d w o r k and c h e e r f u l l y  l o n g and u n u s u a l w o r k i n g h o u r s . locating  tolerated  Many i n d i v i d u a l s  some  assisted i n  c o l o n i e s o r a l l o w e d a c c e s s t o t h e i r p r o p e r t y where  c o l o n i e s were l o c a t e d .  S p e c i a l thanks a l s o go t o t h e Cameron's  a t Pender Harbour, p a r t i c u l a r l y B i l l , Don and J i m , who a l l o w e d us a c c e s s t o t h e i r b a i t ponds a t a l l hours o f t h e day and n i g h t to c a p t u r e and observe h e r o n s .  F i n a l l y ^ I w i s h t o thank my  a d v i s o r s a t U.B.C., p a r t i c u l a r l y Dr. Jamie S m i t h , f o r a d v i c e and d i r e c t i o n  i nwriting  this thesis.  a l l o f t h e above f o r t h e i r a s s i s t a n c e .  I am v e r y g r a t e f u l t o  1 GENERAL INTRODUCTION Great b l u e herons (Ardea h e r o d l a s ) a r e a l a r g e , ous  b i r d d i s t r i b u t e d across North America.  and  feed on a wide v a r i e t y  mammals a n d b i r d s .  conspicu-  Herons a r e p r e d a t o r s  o f f i s h e s , amphibians,  reptiles,  T h e i r h a b i t o f f e e d i n g i n marshes, open  f i e l d s a n d t i d a l a r e a s makes them e a s i l y o b s e r v a b l e , a n d t h e y are a f a m i l i a r sight  i n a r e a s where t h e y o c c u r .  Great  blue  herons n o r m a l l y n e s t i n groups and, once l o c a t e d , h e r o n c o l o n i e s c a n be e a s i l y o b s e r v e d . easy o b s e r v a b i l i t y ,  Because o f t h e i r wide d i s t r i b u t i o n ,  and t h e i r p o s i t i o n near  the top o f the food  c h a i n , h e r o n s were c o n s i d e r e d a p o t e n t i a l l y good species f o r monitoring environmental W i l d l i f e Service 1971).  contamination  (Canadian  T h i s s t u d y was i n i t i a t e d b y t h e  Canadian W i l d l i f e S e r v i c e i n 1977 p r i m a r i l y  t o i d e n t i f y and  enumerate h e r o n c o l o n i e s i n t h e l o w e r m a i n l a n d Columbia  indicator  (Simpson and K e l s a l l 1978).  incorporated into a nation-wide  of British  My s u r v e y s w e r e l a t e r  program t o monitor  great  h e r o n p o p u l a t i o n s (Des G r a n g e s 1980) and t o d e v e l o p t i o n and abundance a t l a s  f o r B.C. ( F o r b e s  In Chapter  a distribu-  et a l . 1983).  T h e r e h a v e b e e n many s t u d i e s o f h e r o n s , t h e i r nesting o r feeding habits^in  blue  most r e l a t i n g t o  t h i s and o t h e r  areas.  I , d a t a c o l l e c t e d a t 15 h e r o n r i e s i n s o u t h  coastal  B.C. i s c o m p a r e d t o h i s t o r i c a l d a t a f o r t h e a r e a a n d t o r e s u l t s of studies i n other areas.  The e f f e c t s o f c o l o n y movements a n d  c h a n g e s i n s i z e , p r e d a t i o n a n d human d i s t u r b a n c e a r e a s s e s s e d by  comparing the r e p r o d u c t i v e performance o f c o l o n i e s s u b j e c t  2 to v a r y i n g i n f l u e n c e s from 1 9 7 7 to I 9 8 O .  In Chapter I I ,  I document the behavior, movements and r e p r o d u c t i v e success o f marked herons w i t h i n one colony i n 1 9 7 8 and 1 9 7 9 * unexpected  Some  c h a r a c t e r i s t i c s o f I n d i v i d u a l s w i t h i n t h i s colony  are r e l a t e d to r e s u l t s from Chapter  I and a i d i n e x p l a i n i n g  some o f the s i z e f l u c t u a t i o n s and movements o f o t h e r heron colonies.  S e v e r a l f a c t o r s c o n s i d e r e d important  to r e p r o -  d u c t i v e success were assessed and o t h e r unforeseen were i d e n t i f i e d .  factors  CHAPTER I  L o c a t i o n , S i z e , H i s t o r y and R e p r o d u c t i v e Success o f H e r o n r i e s i n South C o a s t a l B.C.  4  INTRODUCTION G r e a t b l u e herons (Ardea h e r o d l a s ) have been s t u d i e d i n many a r e a s o f N o r t h A m e r i c a .  Many a u t h o r s r e p o r t t h e l o c a t i o n s ,  numbers o f n e s t s and r e p r o d u c t i v e success i n h e r o n r i e s w i t h i n a g e o g r a p h i c a l a r e a (Des Granges 1 9 8 1 , Werschkul e_t a l . 1 9 7 7 , Vermeer 1 9 7 3 • Benning I 9 6 9 ) .  Heron n e s t s have been found i n a  v a r i e t y o f t r e e s p e c i e s , on man-made s t r u c t u r e s , i n shrubs and even on the ground ( B l u s e t a l . 1 9 8 0 , Des Granges 1 9 7 9 t Vermeer 1970).  Comparison o f h i s t o r i c a l and a n n u a l l y c o l l e c t e d d a t a has  shown t h a t , a l t h o u g h  t h e r e a r e many l o n g - s t a n d i n g h e r o n r i e s ,  c o l o n i e s f l u c t u a t e d r a m a t i c a l l y i n s i z e , a r e abandoned o r r e l o cate f r e q u e n t l y .  The s u s p e c t e d r e a s o n s f o r t h i s  instability  have i n c l u d e d h a b i t a t d e s t r u c t i o n , d i s t u r b a n c e from nearby human a c t i v i t y o r a v i a n predators n e s t i n g i n o r near the h e r o n r i e s . Egg and n e s t l i n g l o s s e s t o p r e d a t o r s and a d u l t I n t e r a c t i o n s w i t h a v i a n p r e d a t o r s have been r e p o r t e d i n many a r e a s 1982,  F r y 1 9 8 0 , Koonz I 9 8 O , Bayer 1 9 7 9 , Werschkul 1 9 7 9 , T a y l o r  and M i c h a e l 1 9 7 1 , The  (Hjertaas  Temple 1 9 6 9 , D u s i and D u s i 1 9 6 8 , Santy 1 9 6 4 ) .  e f f e c t s o f p r e d a t i o n have v a r i e d from minor l o s s e s o f a d u l t s  o r broods t o complete d e s t r u c t i o n and abandonment o f c o l o n i e s . The  response o f herons t o p r e d a t o r s has g e n e r a l l y been i n c o n -  s i s t e n t and u n p r e d i c t a b l e .  The r o l e o f p r e d a t o r s i n a f f e c t i n g  h e r o n r y movements and r e p r o d u c t i o n has, t h e r e f o r e , been d i f f i c u l t to  determine.' A l l r e s e a r c h e r s r e p o r t t h e number o f young r a i s e d p e r  s u c c e s s f u l p a i r and some i n c l u d e an e s t i m a t e o f t h e p e r c e n t a g e o f s u c c e s s f u l p a i r s (see r e v i e w s by P a r k e r 1980, Quinney and  5 Smith 1979, 1.9  McAloney 1973).  young p e r b r e e d i n g  Most h e r o n r i e s produced a t l e a s t  p a i r p e r y e a r , the number b e l i e v e d  s u f f i c i e n t t o m a i n t a i n a s t a b l e heron p o p u l a t i o n i n the n o r t h ern U.S.A. (Henny 1972).  A l t h o u g h t h e r e i s some g e o g r a p h i c  v a r i a t i o n i n the numbers o f young f l e d g e d p e r s u c c e s s f u l n e s t , few d i f f e r e n c e s have been found between c o l o n i e s i n the same a r e a , between y e a r s o r between d i s t u r b e d and colonies.  undisturbed  I n f a c t , the number o f young r a i s e d p e r s u c c e s s f u l  p a i r i s a s u r p r i s i n g l y s t a b l e s t a t i s t i c w i t h " s u r p l u s " young r e p o r t e d f o r the m a j o r i t y o f c o l o n i e s .  The l a c k o f s e n s i t i v i t y  o f t h i s s t a t i s t i c t o v a r y i n g c o n d i t i o n s i n h e r o n r i e s makes i t a poor c h o i c e f o r a s s e s s i n g the r e p r o d u c t i v e h e a l t h o f a heron population. Using d a t a c o l l e c t e d a t 15 c o l o n i e s from 1977  t o 1980,  I have i n v e s t i g a t e d some o f the f a c t o r s t h a t have been suggested to cause h e r o n r y r e l o c a t i o n s and f l u c t u a t i o n s i n s i z e . examined the r e l a t i o n s h i p between p r e d a t o r s I propose a b e t t e r method o f a s s e s s i n g heron  I also  and h e r o n r i e s , and reproductive  success.  METHODS I s t u d i e d 15 c o l o n i e s , 11 o f which were shown t o me by n a t u r a l i s t c l u b s o r i n d i v i d u a l s , and f o u r which were found by ground o r a e r i a l s e a r c h e s . 162 t i m e s from 1977  t o 1979.  I v i s i t e d the 15 study 31 times  {2.2%)  colonies  p r i o r t o the a d u l t  h e r o n s ' a r r i v a l , 66 times (41$) d u r i n g egg l a y i n g and i n c u b a t i o n , and 64 times (40$) d u r i n g the p r e - f l e d g i n g p e r i o d when  6 a d u l t s were seldom p r e s e n t .  In 1980, three persons who had  a s s i s t e d me p r e v i o u s l y d i d the colony surveys.  V i s i t s were  timed to minimize the d i s t u r b a n c e to the colony w h i l e i n g data.  collect-  I questioned r e s i d e n t s and landowners i n the a r e a  o f each colony r e g a r d i n g i t s h i s t o r y , p e r i o d s o f abandonment, l o c a l movements, i n c i d e n c e s o f p r e d a t i o n o r human harassment, and changes i n s i z e . I counted  the t o t a l number o f nest p l a t f o r m s  (unoccupied  nest s i t e s ) and the number o f occupied n e s t s i n each colony i n A p r i l p r i o r to the development o f dense deciduous  foliage.  I Judged p l a t f o r m s to be o c c u p i e d i f there were Incubating a d u l t s present o r i f there were obvious  s i g n s o f a c t i v i t y on  or under the n e s t ( i . e . droppings, h a i r p e l l e t s , food broken branches,  eggshells).  items,  I c o n s i d e r e d n e s t s to be success-  f u l i f there were one o r more young p r e s e n t on the nest i n l a t e June o r e a r l y J u l y , j u s t p r i o r to f l e d g i n g .  At t h a t time young  b i r d s were about two-thirds o f a d u l t s i z e and were r e a d i l y v i s i b l e from the ground.  The number o f young b i r d s was recorded  f o r each n e s t where they c o u l d be a c c u r a t e l y counted. that the numbers o f young counted on these more v i s i b l e were r e p r e s e n t a t i v e o f a l l nests i n each colony.  I assumed nests  I calculated  the mean number o f young f l e d g e d per s u c c e s s f u l nest (MYSN) based on t h i s sample. In two c o l o n i e s , l o c a t e d i n cottonwoods (Populus t r l c h o c a r p a ) , many n e s t s were no l o n g e r v i s i b l e a t f l e d g i n g , so the number o f occupied n e s t s i n A p r i l was used as an estimate o f the number o f s u c c e s s f u l n e s t s each year  (see " R e s u l t s " ) .  The Haney colony  7  was  surrounded by dense c o n i f e r o u s f o r e s t so o n l y a minimum  n e s t count was p o s s i b l e and no f l e d g l i n g counts were made. I mapped e i g h t c o l o n i e s i n I978 and 1979 d u c t i v e I n f o r m a t i o n on i n d i v i d u a l n e s t s .  to o b t a i n r e p r o -  I n a i l e d numbered  aluminum t a g s t o the t r u n k o f each t r e e c o n t a i n i n g one o r more n e s t p l a t f o r m s , whether these were o c c u p i e d o r n o t .  The  loca-  t i o n o f each t r e e was p l o t t e d on graph paper by t a k i n g compass b e a r i n g s and p a c i n g the d i s t a n c e between t r e e s . whether each p l a t f o r m was  s t i l l p r e s e n t , and i f i t was  o r o c c u p i e d on each s u r v e y . l a b e l l e d and mapped.  I recorded vacant  Newly c o n s t r u c t e d n e s t s were a l s o  I n the l a r g e P o i n t R o b e r t s c o l o n y , the  number o f o c c u p i e d n e s t s was  r e c o r d e d i n A p r i l 1978  and a sample o f 40 t r e e s was  l a b e l l e d , mapped and checked  fledging.  and  1979 at  The change i n numbers o f o c c u p i e d n e s t s i n those  40 t r e e s was  used to e s t i m a t e the change i n the e n t i r e c o l o n y  between A p r i l and June.  A s i m i l a r e s t i m a t e was made i n the  C o q u i t l a m c o l o n y u s i n g 17 o f the 35 n e s t t r e e s I n  1979.  The number and c o n d i t i o n o f dead young found on the ground i n each c o l o n y was  r e c o r d e d and some specimens were c o l l e c t e d .  Evidence o f p r e d a t o r s o r scavengers w i t h i n the c o l o n i e s such s c a t s , t r a c k s , owl p e l l e t s , broken eggs and remains o f herons was a l s o r e c o r d e d .  S i g n s o f human a c t i v i t y such as  t r a c k s and f a l l e n t r e e s were a l s o n o t e d .  trails,  as  8  RESULTS Heronry L o c a t i o n s , S i z e s and G e n e r a l D e s c r i p t i o n s F i g u r e 1-1  shows t h e l o c a t i o n s o f t h e 15 s t u d y c o l o n i e s .  I searched f o r nine a d d i t i o n a l c o l o n i e s o f u n c e r t a i n s t a t u s which were r e p o r t e d by Mark ( 1 9 7 6 ) .  I found no e v i d e n c e o f an  a c t i v e c o l o n y a t those s i t e s i n 1977, d e s p i t e e x t e n s i v e ground and a e r i a l s e a r c h e s and c o n v e r s a t i o n s w i t h i n t e r e s t e d n a t u r a l i s t s and persons who had r e p o r t e d t h e c o l o n i e s . t h a t some may have moved t o d i s t a n t , u n r e p o r t e d  I t i spossible locations.  Three o f t h e c o l o n i e s ( M c G l l l i v r a y , Gibsons and C h e h a l i s ) were abandoned t h e y e a r I l o c a t e d them.  The c o l o n i e s I l o c a t e d on  the Sunshine Coast r e p r e s e n t t h e f i r s t * ; w r i t t e n r e c o r d s o f h e r o n r i e s i n t h a t a r e a a l t h o u g h many l o c a l r e s i d e n t s were aware o f them.  I b e l i e v e that the study c o l o n i e s represented a l l o f  the l a r g e r h e r o n r i e s w i t h i n t h e p o p u l a t e d p o r t i o n o f t h e l o w e r mainland.  S m a l l e r c o l o n i e s , and those i n remote a r e a s , may  w e l l have been o v e r l o o k e d . C o l o n i e s v a r i e d from 10 t o 240 s u c c e s s f u l n e s t s i n t h e lower mainland  (Table 1-1)  compared t o a range o f t h r e e t o 130  f o r c o l o n i e s r e p o r t e d by Mark (1976) i n t h e same a r e a s .  The  average s i z e o f t h e f o u r c o l o n i e s r e p o r t e d p r e v i o u s l y by Mark (1976) was 62$ l a r g e r d u r i n g t h i s s t u d y ( T a b l e  1-2).  Herons n e s t e d i n stands o f a l d e r ( A l n u s r u b r a ) , b r o a d l e a f maple (Acer macrophyllum),  cottonwood (Populus  trlchocarpa),  Douglas f i r (Pseudotsuga m e n z l e s i l ) and S i t k a spruce ( P l c e a sitchensls).  Some n e s t s were a l s o found i n w e s t e r n hemlock  (Tsuga h e t e r o p h y l l a ) , l o d g e p o l e p i n e ( P l n u s c o n t o r t a ) and  FIGURE l - l .  Heron colony locations in the lower mainland and Sunshine areas of British Columbia.  Coast  10 T a b l e 1-1.  Number o f s u c c e s s f u l n e s t s i n heron c o l o n i e s surveyed i n south c o a s t a l B r i t i s h Columbia. Number of s u c c e s s f u l nests  Colony name  1977  1978  1979  1980  169  162  31  26  Crescent  37  46  42  22  Edgewater  16  31  38  30  Haney  10*  10*  10*  10*  Mclvor  8  8  5  6  25  33  0  240  236  222  Coquitlam  Pender Harbour Point  Roberts  216  6  Powell R i v e r Salwein  96  Sechelt  "  101 28  .  19  109  91  36  35  S t a n l e y Park  19*  43  38  33  U.B.C.  82  103  118  130  * Minimum count due to v i s i b i l i t y i o r see t e x t .  other l i m i t a t i o n s —  11  Table 1-2.  Comparison o f past and present s i z e s o f f o u r c o l o n i e s In the lower mainland. Before  Colony name  1977- 1980  1976  Mean % increase  mean no. successful nests  N  mean no. successful nests  N  Coquitlam  63  2  97  4  54  McGillivray  27  1  46*  1  70  120  4  228  4  90  80  3  108  4  35  Point  Roberts  U.B.C..  62  Mean * Refers to o c c u p i e d nests l a t e r abandoned, cedar one  (Thuja p l l c a t a ) .  1977.  I n 11 c o l o n i e s ^ h e r o n s nested i n o n l y  t r e e s p e c i e s (Table 1-3), although  o f s i m i l a r h e i g h t i n the same a r e a .  there were o t h e r t r e e s  In a l l c o l o n i e s , most  s u c c e s s f u l nests were i n the same t r e e s p e c i e s (Table  1-3)  and  sites  i n two cases, Coquitlam  i n the primary trees. evidence  and S t a n l e y Park, l i m i t e d  s p e c i e s may have f o r c e d herons to use o t h e r  I have used t h i s c h a r a c t e r i s t i c o f herons as i n d i r e c t t h a t h e r o n r i e s a t d i f f e r e n t l o c a t i o n s , but i n the  same t r e e s p e c i e s , r e p r e s e n t l o c a l movements o f one p o p u l a t i o n . H i s t o r i c a l and P r e s e n t Colony To assess long-term  Data  trends i n the heron p o p u l a t i o n , I  compared p a s t and present d a t a .  Mark (1974,  1976)  summarized  h i s t o r i c a l i n f o r m a t i o n on heron colony l o c a t i o n s and s i z e s .  12 Table  1-3.  Colony name  D e s c r i p t i o n s o f the study No. o f Year s u c c e s s f u l nests*  Tree  colonies •  species  No. o f nest trees  Chehalis  1979  47 31 5 1  B r o a d l e a f maple Cottonwood Douglas f i r Cedar  18  Coquitlam  1978  151 7 4  S i t k a spruce Lodgepole pine Western hemlock  27 5 3  Crescent  1977  37  Douglas f i r  5  Edgewater  1977  16  Cottonwood  3  Gibsons  1978  !;42  ' 1977  Haney  12  B r o a d l e a f maple Red a l d e r  10  Douglas f i r Cottonwood  7 2 1  14 11  2 10  McGillivray  1977  46  Mclvor  1977  8  Pender Harbour  1978  25  Red  alder  23  P o i n t Roberts  1977  216  Red  alder  192  Powell R i v e r  1978  6  Salwein  1977  96  Cottonwood  19  Sechelt  1978  28  Red  28  1978  32 9 2  Douglas f i r Cedar Western hemlock  1977  82 •  Red  Stanley  U.B.C.  Park  Sitka  spruce  Douglas f i r  alder  alder  1  2  3 5 2 61  * R e f e r s to occupied nests f o r c o l o n i e s abandoned p r i o r to f l e d g i n g ( C h e h a l i s , Gibsons, M c G i l l i v r a y ) .  13 I used t h i s and a d d i t i o n a l d a t a from o t h e r p u b l i c a t i o n s and v e r b a l r e p o r t s t o a s s e s s t h e h i s t o r y o f t h e study c o l o n i e s . I assume t h a t v a r i e d l o c a t i o n s o f a c o l o n y w i t h i n 10 k i l o meters i n d i f f e r e n t y e a r s r e p r e s e n t l o c a l movements o f one population. Chehalis  Colony  T h i s c o l o n y was a c t i v e from 1957 t o i960 (Mark 1976). The c o l o n y had been abandoned s h o r t l y b e f o r e my f i r s t on A p r i l 19» 1979•  visit  E g g s h e l l s found on t h e ground had been  broken by p r e d a t o r s o r scavengers and no a d u l t herons were observed.  I found f e a t h e r s o f one dead a d u l t b i r d .  Residents  c o n f i r m e d t h a t the c o l o n y was a c t i v e i n 1978 and t h a t the herons had a r r i v e d , as u s u a l , i n March 1979. ( H a l l a e e t u s l e u c o c e p h a l u s ) which congregate  Bald eagles i n the area to  f e e d on salmon (Oncorhynchus sp.) c a r c a s s e s n o r m a l l y r o o s t i n the f o r e s t e d a r e a where t h e herons n e s t and l e a v e s h o r t l y b e f o r e t h e herons a r r i v e . abandoned t h e i r nests.due l e f t l a t e i n 1979.  R e s i d e n t s s p e c u l a t e d t h a t t h e herons t o harassment by t h e e a g l e s  which  My o b s e r v a t i o n s o f abandoned eggs and one  dead a d u l t support t h a t c o n c l u s i o n . Coquitlam  Colony  Two c o l o n i e s were r e c o r d e d i n C o q u i t l a m .  The Newberry Road  c o l o n y had 78 n e s t s i n spruce t r e e s i n 1971 b u t was abandoned, p r o b a b l y i n 1972, e i t h e r because o f an a d j a c e n t  subdivision  development (Mark 1976), o r because o f a j u v e n i l e banding gram c a r r i e d o u t by a heron r e s e a r c h group w o r k i n g a t t h e  pro-  14 In 1971.  U n i v e r s i t y o f B.C.  94 o f 190  n e s t l i n g s were banded  et a l . 1 9 7 3 ) .  (Campbell  The other colony, on the Essondale 1-1)  (Fig.  , was  f i r s t recorded i n 1973  l e a s t 48 nests (Jerema 1973)•  Indian Reserve when i t contained at  Evidence  i n d i c a t e d t h a t there  had been herons a t t h a t l o c a t i o n f o r many years (Mark 1976) Judging by the s i z e o f the Coquitlam in  1977  and  1978,  Table 1-1),  colony (over 160  and apparent  1979  In  and  1980  existing  1972.  the e a r l i e r n e s t i n g s i t e was  abandoned.  B a l d eagles were n e s t i n g i n the center o f the v a c a t e d T h i r t y - o n e occupied n e s t s were l o c a t e d about one north o f the o l d l o c a t i o n .  nests  overcrowding, i t  i s l i k e l y t h a t the Newberry Road colony j o i n e d an colony at t h i s l o c a t i o n i n  .  Reproduction  colony.  kilometer  i n those n e s t s appeared  to  be normal, but most young had f l e d g e d p r i o r to the census  in  1979.  in  1978  The  s t a t u s o f the remaining  130  p a i r s that nested  i s unknown.  Crescent  Colony  The Crescent colony was  r e f e r r e d to by Urhahn ( 1 9 6 8 ) ,  but no s i z e o f exact l o c a t i o n was r e s i d e n t s , the Crescent colony was f i r s i n Crescent Park but was were f e l l e d .  given.  A c c o r d i n g to l o c a l  o r i g i n a l l y located i n large  f o r c e d to move when the t r e e s  The b i r d s occupied two more s i t e s on p r i v a t e  p r o p e r t y , where they were unwelcome and the t r e e s were f e l l e d , before they found sanctuary a t t h e i r present l o c a t i o n about 1970.  The nest t r e e s are a l l w i t h i n 20 meters o f a p r i v a t e  residence.  T h i s l o c a t i o n was  abandoned f o r two  years about  15 1972-73 when a p a i r o f g r e a t horned owls (Bubo v l r g l n i a n u s ) occupied one o f the n e s t s (R. N i t s c h , p e r s . comm.). The N i t s c h ' s observed three occasions.  eagles c a p t u r i n g young herons on  One eagle landed on a heron nest i n 1978 and  c a r r i e d two young away.  The eagle dropped one young heron i n  the N i t s c h ' s back yard as i t flew away.  The N i t s c h ' s d e t e r r e d  eagle a t t a c k s by f i r i n g a s t a r t e r p i s t o l when eagles approached. Edgewater  Colony  Mark (I976) r e c o r d e d t h i s colony as p r e s e n t i n 197^. Mrs. M. P a s t r l c k  (pers. comm.) i n d i c a t e d t h a t the colony was  o c c u p i e d from 1975 to 1976 and was v i s i t e d r e g u l a r l y by the Langley N a t u r a l i s t s Club.  Many crows (Corvus  present i n t h i s colony a t each v i s i t .  caurlnus) were  The s h e l l s o f s e v e r a l  eggs, a p p a r e n t l y eaten by crows, were found i n A p r i l o f both  1977  and 1978.  Gibson's The  Colony colony was s i t u a t e d about 200 meters from a proposed  sawmill s i t e .  The m i l l s i t e was c l e a r e d to the outermost nest  and e x t e n s i v e e x c a v a t i n g began i n 1978 and continued i n 1979. The  colony was occupied i n A p r i l  but was abandoned i n both y e a r s . colony.  1978 and a g a i n i n May 1979 Many crows were seen i n t h i s  Eggs l a i d i n 1978 were eaten on the nest  probably a f t e r the a d u l t s l e f t , on the n e s t s .  platforms  judging by the s h e l l s  found  A p o s s i b l e p r e v i o u s nest s i t e nearer the Gibson's  town s i t e was not r e o c c u p i e d d u r i n g t h i s time.  Two n e s t s were  16 occupied and s u c c e s s f u l i n 1980, i n d i c a t i n g t h a t more herons may r e t u r n to t h i s s i t e i n the f u t u r e . Haney Colony Mark (1976) r e p o r t e d t h a t t h i s colony was f i r s t i n 1974.  I t was a l s o a c t i v e from  U.B.C. Research  Forest s t a f f .  formed  1975 to 1976, a c c o r d i n g to  Accurate nest and f l e d g l i n g  counts i n t h i s colony a r e impossible due to the dense c o n i f erous f o l i a g e surrounding the n e s t s . A r e d - t a i l e d hawk (Buteo  jamaicensis) buzzed the colony  in April  1977. and v i s i t o r s r e p o r t e d t h a t eagles harassed the  colony.  I found^a d e c a p i t a t e d young heron under the n e s t s i n  June 1977. c o n f i r m i n g p r e d a t i o n by eagles o r owls. McGillivray  Colony  The M c G i l l i v r a y colony was present s i n c e a t l e a s t (Mark 1976).  1974  L o c a l n a t u r a l i s t s i n d i c a t e d t h a t i t was a c t i v e  u n t i l 1977. although no systematic r e c o r d s were kept.  On  March 10, 1977. 46 nests were occupied, although I d e s c r i b e d the b i r d s ' behavior as "very spooky and e a s i l y d i s t u r b e d . " Many n e s t s were abandoned by May 6 and most (43) by May 18, 1977.  An occupied e a g l e s ' nest was found 200 meters east o f  the colony i n A p r i l  1978  1978.  The colony was not r e o c c u p i e d i n  o r 1979.  Mclvor  Colony  The Mclvor colony c o u l d be one o f s e v e r a l r e f e r r e d to by Mark (1976)  i n the P i t t Meadows a r e a .  Residents s a i d i t had  been a t t h i s l o c a t i o n s i n c e 1970 and averaged  10 n e s t s a year.  17 Eagles f r e q u e n t l y harassed taken.  the nests but no young were seen  A t l e a s t f i v e young f e l l  from the nests i n 1977.  The nest t r e e was three meters from a p r i v a t e r e s i d e n c e b u i l t i n 1976. Pender Harbour  Colony  The Pender Harbour heronry was found on a p r o p e r t y b e i n g s u b d i v i d e d f o r r e s i d e n t i a l l o t s 200 meters south o f Gunboat Bay.  The colony had been a t that l o c a t i o n s i n c e a t l e a s t  when i t was estimated to c o n t a i n 75 nests comm.).  1963  (A. J o s s , p e r s .  I t contained 43 o c c u p i e d nests i n 1978 and 45 occu-  p i e d nests i n 1979. The  colony was bounded on the east and n o r t h by s u b d i v i s i o n  l o t s and a new access road r e s p e c t i v e l y , while the southernmost nests were exposed to view from Highway 101 by removal o f the trees.  The s u b d i v i s i o n work began i n the summer o f 1977 and  continued through  the s p r i n g and summer o f 1978.  Extensive  e x c a v a t i n g and some b l a s t i n g were r e q u i r e d to i n s t a l l water mains i n A p r i l and May and two water w e l l s were d r i l l e d i n June 1978.  The work was completed i n the s p r i n g o f 1979 and  there was no f u r t h e r road work o r house c o n s t r u c t i o n a f t e r A p r i l o f 1979.  During the c o n s t r u c t i o n work i n 1978, a d u l t  herons were f r e q u e n t l y f r i g h t e n e d from t h e i r n e s t s . I observed  eagles t a k i n g young herons from t h e i r nests  w i t h a d u l t s present on two o c c a s i o n s i n 1978 and three o t h e r eagle a t t a c k s were r e p o r t e d (M. Wise, p e r s . comm.). (Corvus  Ravens  corax) were commonly present i n the colony and I  18  o b s e r v e d them t a k i n g s i x young from u n p r o t e c t e d n e s t s i n 1978 and 1 9 7 9 .  Ravens p u l l e d young herons from t h e i r n e s t s , i n the  absence o f a d u l t s , and a t e them on the ground. e v i s c e r a t e d young on the ground i n 1 9 7 8 . of  three adult k i l l s  (A83)  i n 1978.  I found  I a l s o found  14 evidence  ( f e a t h e r s ) i n c l u d i n g one banded a d u l t  E a g l e s n e s t i n g i n a l a r g e f i r o v e r l o o k i n g the  c o l o n y appeared to use the herons as a c o n v e n i e n t f o o d s u p p l y . I found heron bones and f e a t h e r s under the e a g l e s E a g l e s d i d not n e s t t h e r e i n 1979  1978.  when the h e r o n r y was In  1  nest i n  but r e t u r n e d i n I 9 8 O  abandoned.  1979 a t o t a l o f 12 p a i r s , which attempted n e s t i n g ,  f a i l e d to f l e d g e any young.  Three n e s t s were o c c u p i e d by  a d u l t s and abandoned p r i o r to egg l a y i n g .  Four o t h e r n e s t s  c o n t a i n e d s m a l l young, j u d g i n g by s h e l l s found on the ground, but the young were l o s t and the n e s t s abandoned s h o r t l y a f t e r hatching.  I n such cases i t i s i m p o s s i b l e t o t e l l i f l o s s o f  the young i s the cause o r the r e s u l t o f the abandonment. Two  n e s t s , each c o n t a i n i n g t h r e e l a r g e young, were robbed,  p r o b a b l y by raccoons  (Procyon l o t o r ) , between June 17 and  24.  The n e s t s were covered w i t h f e a t h e r s and chewed bones and r a c c o o n t r a c k s were found on the ground under the n e s t s . I found f o u r dead young under two o t h e r empty n e s t s from ravens had attempted  to p u l l young on e a r l i e r d a t e s .  I n one  o t h e r n e s t t h r e e l a r g e young d i s a p p e a r e d between June 20 24 p r i o r to f i r s t f l e d g i n g .  I s u s p e c t e d e a g l e s but no  a t t a c k s were o b s e r v e d i n 1 9 7 9 »  which  and  eagle  19 A d u l t herons In the Pender Harbour area were banded i n 1978 and  1979 a t f e e d i n g a r e a s .  observed  i n the colony (see Chapter I I ) .  P o i n t Roberts  Many o f the banded b i r d s were  Colony  A colony o f 165 nests (1948) and  I85 nests (1949)  was  o r i g i n a l l y l o c a t e d near R a l t t Road i n D e l t a M u n i c i p a l i t y and was  d i s p l a c e d a s h o r t d i s t a n c e by power l i n e  (E. T a y l o r , p e r s . comm.). same area was  In 1959 a 100-nest  clearing colony i n the  destroyed by c l e a r i n g o f the cottonwood and  a l d e r nest t r e e s f o r a r e s i d e n t i a l development (Mark 1974). Another colony o f unknown s i z e i n south P o i n t Roberts recorded as destroyed by development about 1970 In 1973 a colony o f 30 nests was  was  (Mark 1974).  l o c a t e d o f f C h u r c h i l l Road  j u s t south o f the Canada-U.S.A., boundary (Mark 1974).  The  P o i n t Roberts  1-1)  was  colony c o n t a i n i n g over 200 nests (Table  at t h i s l o c a t i o n from  1977 to I98O.  I f the nest  counts  from p r e v i o u s years are c o r r e c t , i t i s l i k e l y t h a t the colony s p l i t up from  1958  to 1973 and has r e c e n t l y re-congregated  a t the C h u r c h i l l Road l o c a t i o n .  I b e l i e v e t h a t a l l the herons  n e s t i n g i n South D e l t a - P o i n t Roberts are now  a t the one l a r g e  colony. Judging from t r a c k s , domestic v i s i t e d the heronry.  dogs and c a t s f r e q u e n t l y  Some t r e e s near the edge o f the colony  were felled"<by woodcutters  and two nest t r e e s had been chopped  but not f e l l e d , probably by c h i l d r e n p l a y i n g with an  axe.  20 Powell R i v e r  Colony  The Powell R i v e r colony was l o c a t e d i n a dense f o r e s t o f immature Douglas f i r and western hemlock behind S t r e e t Elementary (Table 1-1) .  Abbotsford  School i n 1978 and contained s i x nests  Three former n e s t i n g s i t e s were l o c a t e d , i n c l u d -  i n g one which c o n t a i n e d 16 n e s t s i n 1974 (C. Burton, comm.).  pers.  Dense second growth f o r e s t i n the P o w e l l R i v e r area  and l i m i t e d access prevented l o c a t i o n o f o t h e r a c t i v e  heron-  The colony contained 19 a c t i v e nests i n 1980 (Table  ries. Salwein  1-1).  Colony  The Salwein colony was l o c a t e d i n l a r g e cottonwoods about 100 meters from the Canadian Forces wet b r i d g i n g p r a c t i c e area ( F i g . 1-1). euvers.  The a r e a i s a s i t e o f frequent mock combat man-  The colony was f i r s t recorded i n the B.C. Nest Record  Scheme i n 1976 and had an estimated 50 n e s t s . s i z e i n 1977 to 96 n e s t s  (Table 1-1)  The i n c r e a s e d  c o i n c i d e d with the  abandonment o f the M c G i l l l v r a y colony about e i g h t k i l o m e t e r s away.  I b e l i e v e t h a t many o f the M c G i l l l v r a y herons  shifted  to the Salwein colony i n the s p r i n g o f 1977. A p a i r o f great horned owls nested i n the colony i n 1979. A r e d - t a i l e d hawk harassed  the herons i n A p r i l and May 1977.  F i v e dead and one l i v e young were found on the ground on May 3 0 , 1978. Sechelt  Colony  I l o c a t e d the S e c h e l t colony i n March 1978 about k i l o m e t e r s north-west o f P o r p o i s e Bay.  1.5  The h i s t o r y o f the  21 colony i s unknown; but o t h e r r e p o r t e d l o c a t i o n s i n c l u d e Four M i l e P o i n t on the n o r t h shore o f P o r p o i s e Bay, Marsh a t the head o f the bay.  and S e c h e l t  Dense undergrowth i n the l o g g i n g  s l a s h through which the colony i s reached makes access c u l t so i t i s u n l i k e l y that the colony s u f f e r s any d i s t u r b a n c e from  direct  people.  I found s i x dead young on the ground and saw hanging  diffi-  from n e s t s i n 1 9 7 8 .  No crows were observed  three o t h e r s  A l l o f the dead b i r d s were i n t a c t .  i n the c o l o n y but I saw a r e d - t a i l e d  hawk h a r a s s i n g a d u l t s on two o f the f o u r v i s i t s 1 9 7 9 I r e c o r d e d two nest f a i l u r e s a t S e c h e l t .  in 1978. No  In  dead young  were found under those n e s t s although, under o t h e r t r e e s , s i x dead young were found, o f which one had been eaten. S t a n l e y Park  Colony  There has been a heron least  colony i n S t a n l e y Park s i n c e a t  1 9 2 1 when 3 9 n e s t s were recorded a t Brockton P o i n t .  Table 1-4  shows the l o c a t i o n s and numbers o f n e s t s i n the  colony from  1921  to I 9 8 O .  The  exact date o f the move from  Brockton P o i n t to the zoo a r e a c o u l d not be A newspaper a r t i c l e  determined.  i n 1 9 2 8 s t a t e d t h a t the dead spruce t r e e  a t Brockton P o i n t , where the b i r d s nested, was  to be removed.  A photograph o f the t r e e showed 2 7 n e s t s and 81 young d u r i n g the " l a s t " n e s t i n g season.  I t i s probable t h a t the colony  has moved a t l e a s t twice s i n c e 1 9 2 1 . was  p r o b a b l y an underestimate  The nest count  in  1977  s i n c e I d i d not check o t h e r  t r e e s i n the v i c i n i t y o f the two  l a r g e " f i r s used that y e a r .  22 Table 1-4.  S i z e and l o c a t i o n s o f the S t a n l e y Park colony from 1921 to 1980.  Date  Successful nests  Location  1921  39  Brockton P o i n t  Mark (1976)  1923  23  Brockton P o i n t  Mark (1976)  1928  27  Brockton P o i n t  Vancouver Sunday P r o v i n c e June 17, 1928  1959  25  Brockton P o i n t  Mark (1976)  1961  25+  Exact l o c a t i o n not s p e c i f i e d  Mark (1976)  1966  28  Exact l o c a t i o n not s p e c i f i e d  Mark (1976)  1967  40  Exact l o c a t i o n not s p e c i f i e d  Mark (1976)  1968  25  Exact l o c a t i o n not s p e c i f i e d  Mark (1976)  1969  Active  Exact l o c a t i o n not s p e c i f i e d  Mark (1976)  1970  40  Exact l o c a t i o n not s p e c i f i e d  Mark (1976)  1971  30  Zoo a r e a  Paine  1974  21  Zoo a r e a  Mark (1976)  1977  19  Zoo a r e a  Simpson and K e l s a l l (1977)  1978  43*  Zoo area  1979  38  Zoo a r e a  1980  33  Zoo a r e a  Source  (1976)  * Twenty-nine n e s t s i n the two Douglas f i r s and 14 n e s t s l o c a t e d i n hemlock and cedar around the aquarium.  23 T h i s colony i s unique i n that i t i s i n the c e n t e r o f a v e r y h i g h use r e c r e a t i o n area and the nests are r e a d i l y v i s i b l e from the ground.  The herons are a p p a r e n t l y u n d i s t u r b e d by  human a c t i v i t i e s on the ground.  No a v i a n p r e d a t o r s or  scaven-  gers were observed at t h i s colony although e a g l e s , ravens  and  crows are present i n the park. U.B.C. Colony A colony o f 40 n e s t s was  r e p o r t e d on the north shore o f  Sea I s l a n d i n 19^1 and remained a c t i v e u n t i l 19^9. destroyed by a i r p o r t expansion about 1950  It  was  (Mark 1976).  The  b i r d s o f t h a t colony probably moved to the U.B.C. colony (Fig.  1-1).  The U.B.C. colony was  first  enumerated i n  1970  when i t c o n t a i n e d 125 n e s t s . In  December 1970 a b l i n d was  b u i l t on the p e r i p h e r y o f  the colony f o r use i n the summer o f 1971  (Paine  1972).  Occupancy o f t h a t b l i n d r e s u l t e d i n the immediate abandonment of  the three c l o s e s t n e s t s .  to  the colony one month l a t e .  e a r l y May,  The main group o f b i r d s r e t u r n e d I n c u b a t i o n , which began i n  and the f i r s t n e s t l i n g , observed on May  equally l a t e .  During  20, were  1971 the colony c o n t a i n e d about 55 n e s t s ,  with another 20 l o c a t e d 200 meters n o r t h o f the main c o l o n y . The  " s a t e l l i t e " contained poor q u a l i t y n e s t s , and was  t i o n a l three weeks l a t e r than the main c o l o n y . was  approximately  1973)•  75»  50 l e s s than lh:1970  In 1972 the main colony was  " s a t e l l i t e " contained 22 n e s t s . and the d e c l i n e was  thought  an a d d i -  The nest  (Campbell  abandoned and  count  et a l .  the  No o t h e r n e s t s were found  to be caused by " . . . l o s s e s to the  24 b r e e d i n g p o p u l a t i o n due  to severe w i n t e r s , " ( J . Krebs I n :  Campbell e t a l . 1974, p. 2 2 ) . I n 1971, 1973).  106 o f 176 young were banded (Campbell  I n 1972,  57 o f 62 young were banded.  et a l .  Those e f f o r t s  would have i n v o l v e d c l i m b i n g almost e v e r y t r e e i n the c o l o n y and r e q u i r e d s e v e r a l days o f c o n t i n u o u s d i s t u r b a n c e each y e a r . I n 1973 and 1974 was  the r e s e a r c h a c t i v i t y stopped, and the c o l o n y  r e c o r d e d as b e i n g a c t i v e w i t h no n e s t counts I n 1977  (Mark 1974).  t h e r e were 70 n e s t s i n the s a t e l l i t e c o l o n y w h i l e  the main c o l o n y remained abandoned.  A check on l a t e n e s t i n g  on J u l y 19 r e v e a l e d 12 a d d i t i o n a l n e s t s a p p r o x i m a t e l y meters northwest  o f the c o l o n y (Area A ) .  The presence  100 of  l o u d l y - c a l l i n g u n f l e d g e d young a t t r a c t e d a t t e n t i o n to t h a t l o c a t i o n , and i n d i c a t e d t h a t the group b r e d about t h r e e weeks l a t e r than the s a t e l l i t e c o l o n y , which had few u n f l e d g e d young. I n A p r i l o f 1978  the s a t e l l i t e c o l o n y had i n c r e a s e d by  4 l n e s t s over the 1977  count.  There were 19 I n a c t i v e n e s t  s i t e s i n A r e a A and a n o t h e r s e p a r a t e group (Area B) c o n t a i n i n g 24 nests,, a l s o i n a c t i v e .  I f the m a j o r i t y o f those 43 a l t e r n a t e  n e s t s had been a c t i v e i n 1977, n e s t s i n 1978  then the observed  increase i n  can be e x p l a i n e d s i m p l y by a s h i f t o f the p e r i -  p h e r a l b i r d s back to one l a r g e c o l o n y . I t seems l i k e l y t h a t the observed  decreases  i n 1971  1972 were r e l a t e d to herons abandoning d i s t u r b e d s i t e s r e l o c a t i n g elsewhere  i n undiscovered s i t e s .  and and  I n 1979 a l l o l d  l o c a t i o n s o f t h i s c o l o n y were c o m p l e t e l y abandoned and a and l a r g e r c o l o n y o f 118 n e s t s was  formed about t h r e e  new  25 k i l o m e t e r s to the e a s t . occupied  A l l the newly c o n s t r u c t e d nests were  i n June 1979•  Four dead young were found on the ground and s i x dead young were seen on nests i n 1978.  I saw a raccoon  young heron on the ground i n 1978 and raccoon common under the heronry.  eating a  t r a c k s were  An eagle flew over the colony dur-  i n g one v i s i t , butv.did not cause a d u l t s to l e a v e t h e i r n e s t s . Reactions  to Human Disturbance  In two c o l o n i e s l o c a t e d w i t h i n 20 meters o f p r i v a t e r e s i dences (Crescent and M c l v o r ) , and one l o c a t e d i n a h i g h l y developed  park ( S t a n l e y P a r k ) , the herons were  unconcerned d u r i n g o b s e r v a t i o n a l v i s i t s .  completely  I n s i x other lower  mainland c o l o n i e s , which were surrounded by f o r e s t but c l o s e to populated  areas, herons r e a c t e d to r e s e a r c h e r s by c a l l i n g ,  r a i s i n g f e a t h e r s and standing but remained on o r near nests.  A t both Pender Harbour ( A p r i l  their  1978) and M c G i l l i v r a y  (March 1977) most b i r d s f l e d as the c o l o n i e s were approached. When nest t r e e s were climbed, b i r d s flew from that t r e e and a l s o from nearby t r e e s . g i v i n g continuous, one  Most b i r d s c i r c l e d the colony  l o u d c a l l s when d i s t u r b e d .  However, on  o c c a s i o n an a d u l t b i r d a c t i v e l y defended i t s nest a g a i n s t  the c l i m b e r by p h y s i c a l l y b l o c k i n g h i s path, s t r i k i n g a t him and  f l a r i n g i t s wings.  Reproductive  Success  I measured r e p r o d u c t i v e success a t most c o l o n i e s from 1977 to 1980 by c a l c u l a t i n g the mean number o f young f l e d g e d p e r  26 s u c c e s s f u l nest  (MYSN) ( F i g . 1-2).  I compared MYSN between  c o l o n i e s and between years f o r the f i v e lower mainland  colonies,  f o r which I had f l e d g i n g estimates each year, by a n a l y s i s o f variance.  There were no s i g n i f i c a n t d i f f e r e n c e s between years  or between c o l o n i e s .  I compared MYSN between a l l c o l o n i e s i n  1978 and 1979 by a n a l y s i s o f v a r i a n c e .  There were no d i f f e r -  ences between c o l o n i e s i n 1979 and few d i f f e r e n c e s i n 1978. The Pender Harbour and Mclvor c o l o n i e s had lower MYSN than the U.B.C. and Crescent c o l o n i e s i n 1978 (p < .05, Duncan's M u l t i p l e Range T e s t ) . I f o l l o w e d the f a t e o f i n d i v i d u a l nest p l a t f o r m s i n e i g h t c o l o n i e s i n 1978 and two i n 1979.  Although  the s t a t u s o f some  p l a t f o r m s was undetermined d u r i n g each survey, minimum numbers o f n e s t s abandoned and newly o c c u p i e d o r c o n s t r u c t e d betxvreen surveys were o b t a i n e d (Table 1-5).  At most c o l o n i e s , the  number o f a d d i t i o n s exceeded the number abandoned over the n e s t i n g season.  At Pender Harbour and U.B.C. the number o f  n e s t s abandoned exceeded the number newly occupied, a s i g n i f i cant d i f f e r e n c e from the combined p r o p o r t i o n o f other c o l o n i e s (Table 1-5, x  2  = 13.3. 3 d f , p < . 0 1 ) .  Both o f these c o l o n i e s  were completely abandoned the next year. data I was a b l e to determine  Using abandonment  the number o f breeding  pairs,  both s u c c e s s f u l and u n s u c c e s s f u l , and c a l c u l a t e d the mean number o f young f l e d g e d per breeding p a i r  (MYBP)' (Table 1-6).  MYSN was s i g n i f i c a n t l y g r e a t e r than MYBP ( t = 3.88, p < .01) by 15$ on average nest abandonment was h i g h .  9 df,  and by up to 50$ i n cases where  N O |UJ CO C2> UJ Q Z  mi  u_  H I  CD CO Z CO  oo >- o o to  +  i  42 4 3 2 6  18 17 13 2 2  1977 78 8 0  77 78 79 80  77 7 9 8 0  PORT CRESCENT COQUITLAM  EDGEWATER  FIG. 1-2  Mean numbers of  II  12 10  8  6  5  6  77 78 79 80  MclVOR  19 32  39 39 3 3 53  34 43  14  13 2 8  12 2 2 18 19  2 3 3 0 21 51  78 7 9  7 7 78 7 9 8 0  77 80  78 79 80  7 7 78 7 9 80  77 78 79 8 0  STANLEY PARK  UBC  PENDER HARBOUR  POINT SALWEIN SECHELT ROBERTS  young f l e d g e d per successful nest at 10 heronries  from  1977 to  1980.  Table 1-5.  Number o f nests abandoned and newly-occupied e i g h t c o l o n i e s i n 1978 and two i n 1979.  Time p e r i o d  Colony  No. occupied i n Mar/Apr  between survey dates a t  No. No. newly abandoned occupied o r or f a l l e n constructed by J u n / J l y Mar-Jly  No. successf u l nests  7-Jun 27  141  9  30  162  Crescent  Apr 21-Jun 29  39  5  12  46  Mclvor  Apr  9  1  0  8  Pender Harbour  Apr 3 0 - J l y 17, 78 Mar 3 1 - J l y 13, 79  33 44  14  6 1  25 33  Point  Apr 21-Jun 29  221  21  24  6 7  28  31  2 2  Coquitlam  Apr  1  Roberts  2  12-Jun 27  12  40  240  Sechelt  Apr 1 9 - J l y 17. 78 Mar 2 7 - J l y 14, 79  S t a n l e y Park  Apr  5-Jun 28  43  1  1  43  U.B.C.  Apr  11-Jun 30  107  19  15  103  1.  Estimated from 17-tree sample.  2.  Estimated from 40-tree  sample.  36  Table  1-6.  Mean numbers o f young fledged per s u c c e s s f u l nest and per breeding at e i g h t c o l o n i e s i n 1978 and two i n 1979. Mean young f l e d g e d / s u c c e s s f u l nest (MYSN)  Colony  Mean young f l e d g e d / breeding p a i r (MYBP)  % difference  Coquitlam  2.3  2.2  4.5  Crescent  2.8  2.5  12.0  Mclvor  2.1  1.9  10.5  2.1 3.0  1.4  50.0 36.4  2.5  2.3  8.7  2.6 2.8  2.4 2.6  8.3 7.7  Stanley Park  2.6  2.6  0.0  U.B.C.  2.8  2.4  16.7  2.56  2.25  15.5  Pender Harbour  1978 1979  P o i n t Roberts Sechelt  1978 1979  Mean (unweighted)  pair  30 At most c o l o n i e s the number o f o c c u p i e d n e s t s and  the  p e r c e n t o f the t o t a l p l a t f o r m s o c c u p i e d d i d not f l u c t u a t e much over the breeding season  (Table 1-7).  To determine  o f n e s t s abandoned, each nest must be l a b e l l e d and on subsequent v i s i t s .  the number rechecked  Counts o f n e s t s do not p r o v i d e abandon-  ment data because nest a d d i t i o n s between surveys f o r nest l o s s e s (Table 1-5).  compensate  L a b e l l i n g i n d i v i d u a l nests  repeated surveys are time consuming and may  and  cause n e s t i n g  d i s r u p t i o n s and l o s s e s i n c o l o n i e s unaccustomed to human intrusions.  I found that the number o f n e s t s abandoned  and,  thereby, the t o t a l number o f breeding p a i r s a t each colony, c o u l d be estimated u s i n g the percentage at fledging  ( F i g . 1-3)•  o f p l a t f o r m occupied . 5  As the percentage  o f n e s t s abandoned  i n c r e a s e d , the p r o p o r t i o n o f p l a t f o r m s o c c u p i e d a t f l e d g i n g decreased, d e s p i t e the confounding  e f f e c t o f nest a d d i t i o n s .  DISCUSSION Colony S i z e s The absence o f nine p r e v i o u s l y r e p o r t e d c o l o n i e s and suspected amalgamation o f the Newberry-Coqultlam M c G i l l i v r a y - S a l w e i n c o l o n i e s suggest  and  t h a t the r e c e n t i n c r e a s e  i n s i z e s o f e x i s t i n g h e r o n r i e s (Table 1-2) the amalgamation o f s m a l l e r c o l o n i e s .  the  has r e s u l t e d  from  Frequent r e f e r e n c e to  c l e a r i n g f o r developments and power l i n e s suggests t h a t urban expansion and l o s s o f f o r e s t e d n e s t i n g h a b i t a t i s l i k e l y  res-  p o n s i b l e f o r c o n c e n t r a t i n g herons i n fewer and l a r g e r breeding colonies.  Table 1-7.  Number and % o f nest platforms occupied d u r i n g the breeding at eight heronries. Coquitlam Crescent  m4 4 j Time p e r i o d  Incubating A p r i l 1978  N  #  68  91  Young p r e s e n t May-June 1978  N  #  Pender Harbour  Mclvor  1  N  #  N  $  N  9  90  39  42  , 3 7 95  8  80  43  46  46  8  80  25  27  33  35  4  Point Roberts  2  .  #  47  98  Stanley Park3  Sechelt N  #  season  N  #  24  73  30  100  28  88  31  100  28  88  30  97  36  95  U.B.C. N  $  111  85  103  77  Fledging June-July 1978  78  94  87  J u l y 1979  51  91  1.  17-tree sample.  2.  40-tree  3.  Nests i n two l a r g e Douglas f i r s o n l y .  4.  Sample o f nests examined by a t r e e climber i n 1977.  sample.  32  FIG. 1-3 The relationship between the percentage of nest platforms occupied at fledging and the percentage of unsuccessful pairs at eight colonies in 1978 and two In 1979.  33 1977  Data f o r nine c o l o n i e s i n the lower mainland from to 1979  showed t h a t the s m a l l e s t decreased  n e s t s to f i v e , one  decreased  due  i n s i z e from e i g h t  to abandonment o f i t s o r i g i n a l  s i t e , one remained s t a t i c and the o t h e r s i x i n c r e a s e d i n s i z e from nine to 138$.  In 1980,  most c o l o n i e s showed s l i g h t  d e c l i n e s , r a n g i n g from s i x to 17% t i o n s can best be understood  (Table 1-1).  by c o n s i d e r i n g the  These  fluctua-  circumstances  and h i s t o r y o f each colony. Increase i n the U.B.C. colony i n 1978  The  was  probably  the r e s u l t o f the r e t u r n o f a d u l t s from a l t e r n a t e n e s t i n g s i t e s to one  c e n t r a l nesting area.  In 1979  c a t e d and c o n t a i n e d 118 a c t i v e n e s t s .  the e n t i r e colony r e l o I n I98O i t i n c r e a s e d to  130 n e s t s , f i v e more than the p r e v i o u s h i g h count o f 125 i n 1970.  The  same phenomenon may  suggests  t h a t the colony has  ing s i t e .  Interchange  be r e s p o n s i b l e f o r changes  Complete abandonment i n 1972  a t the Crescent colony.  nests  and  1973  some undiscovered a l t e r n a t e n e s t -  between s i t e s c o u l d account  f o r year-  to-year v a r i a t i o n s i n numbers o f o c c u p i e d n e s t s , independent o f a c t u a l changes o f p o p u l a t i o n .  The l a r g e i n c r e a s e i n s i z e  o f the S t a n l e y Park colony from 19 to 43 nests I n d i c a t e s a g a i n the apparent sites.  m o b i l i t y o f g r e a t b l u e herons i n choosing nest  Based on p r e v i o u s y e a r s ' data (Table 1-4),  38 nests  i s not u n u s u a l l y l a r g e f o r the S t a n l e y Park c o l o n y . n e s t counts o f 1971.  1974  and  1977  The  low  c o u l d w e l l be the r e s u l t  o f f a i l u r e to l o c a t e o t h e r n e s t s i n the g e n e r a l a r e a . C o l o n i e s i n the Sunshine Coast a r e a have shown s i m i l a r fluctuations.  S u c c e s s f u l n e s t s a t Pender Harbour and S e c h e l t  34 i n c r e a s e d by almost o n e - t h i r d from  19?8 to 1979 (Table 1 - 1 ) ,  although h i s t o r i c a l data i n d i c a t e d t h a t the Pender Harbour colony may have been l a r g e r p r e v i o u s to the s u b d i v i s i o n ment t h e r e .  develop  I n 1980 the Pender Harbour colony was completely  abandoned w h i l e the S e c h e l t c o l o n y remained s t a b l e and the s m a l l Powell R i v e r colony t r i p l e d i n s i z e Coquitlam colony dropped from  (Table 1-1).  The  162 n e s t s i n 1978 to 31 n e s t s  i n 1979. Such massive changes i n c o l o n y s i z e from year to year cannot be e x p l a i n e d i n terms o f a d u l t m o r t a l i t y o r recruitment.  The death o f 260 a d u l t herons i n Coquitlam  c o u l d s c a r c e l y have gone u n n o t i c e d . The abandonment o f the M c G i l l i v r a y c o l o n y and the conc u r r e n t i n c r e a s e a t the Salwein c o l o n y lends f u r t h e r  support  to the i d e a o f the a d u l t movement between c o l o n i e s .  I t may be  i n f e r r e d t h a t , although herons p r e f e r t o nest i n groups, the presence  o f one group does not p r e c l u d e the e x i s t e n c e o f  o t h e r s i n the same l o c a l i t y .  In f a c t , the presence o f one  c o n c e n t r a t i o n i s o f t e n a s s o c i a t e d with one o r more a l t e r n a t e s i t e s among which breeding a d u l t s may r e l o c a t e from.year to year. R e a c t i o n s to Human Disturbance Marked d i f f e r e n c e s were noted i n the response o f herons i n some c o l o n i e s to the presence o f people.  These ranged  no r e a c t i o n , to standing and c a l l i n g , to t a k i n g f l i g h t .  from Those  v a r i e d r e a c t i o n s to the same s t i m u l u s imply t h a t herons have d i f f e r e n t t o l e r a n c e l e v e l s to humans i n d i f f e r e n t  locales.  35 In g e n e r a l , c o l o n i e s l o c a t e d c l o s e to areas o f human a c t i v i t y showed l e s s response  than those i n more remote a r e a s .  Some i n d i v i d u a l s w i t h i n c o l o n i e s were a l s o more t o l e r a n t or l e s s a f r a i d than o t h e r s .  I b e l i e v e t h a t many o f the herons  a t Pender Harbour which s u c c e s s f u l l y r a i s e d young i n 1978 d i d so because they remained on t h e i r n e s t s d e s p i t e the d i s t u r bance from c o n s t r u c t i o n nearby. N e s t i n g herons c o u l d b e n e f i t from a c l o s e a s s o c i a t i o n with people  i f p r e d a t o r s a r e l e s s t o l e r a n t o f humans.  d e t e r r e n c e o f eagle a t t a c k s by landowners probably p r e d a t i o n a t the Crescent c o l o n y .  The presence  The  reduced  o f people and  r e s i d e n c e s near o t h e r c o l o n i e s may have i n h i b i t e d the a c t i v i t y o f some p r e d a t o r s .  The s c a r c i t y o f p r e d a t o r s a t S t a n l e y Park  may r e s u l t from i n t e n s e human a c t i v i t y . Predation I observed  a v i a n o r t e r r e s t r i a l p r e d a t o r s i n every heron  colony except S t a n l e y Park.  I r e c o r d e d eagle o r owl n e s t s a t  f i v e c o l o n i e s , eagle o r hawk harassment a t seven, ravens a t seven and mammalian c a r n i v o r e s a t t h r e e .  crows o r Predators  are probably a t t r a c t e d to h e r o n r i e s because o f the young and eggs i n the n e s t s and by the food items and young  falling  from t h e n e s t s . I b e l i e v e t h a t p r e d a t i o n was a s i g n i f i c a n t cause o f nest f a i l u r e a t some heron c o l o n i e s , e s p e c i a l l y a t Pender Harbour. Fourteen e v i s c e r a t e d young found a t Pender Harbour i n 1978 were probably k i l l e d by ravens.  Seven i n t a c t young found a t  36 S e c h e l t probably f e l l a c c i d e n t a l l y from t h e i r nests s i n c e they were not eaten.  My other o b s e r v a t i o n s i m p l i c a t e d preda-  t o r s i n f i v e o f 12 nest f a i l u r e s a t Pender Harbour i n 1979. Heavy l o s s e s to p r e d a t i o n at Pender Harbour were probably p r e d i s p o s e d by the frequent absence o f a d u l t herons from n e s t s which, i n t u r n , was nearby.  the  caused by the c o n s t r u c t i o n work  P r e d a t o r s a p p a r e n t l y became accustomed to the r e a d i l y  a v a i l a b l e food supply a f f o r d e d by unprotected n e s t s . a t t a c k s witnessed o c c u r r e d with a d u l t s i n attendance  The  a t the  n e s t s , however, i n d i c a t i n g t h a t any i n h i b i t i o n t h a t may p r o v i d e d n o r m a l l y by a d u l t s , was  not o p e r a t i n g .  Other s t u d i e s  have i n d i c a t e d t h a t complete nest l o s s e s a r e p r o b a b l y 1972).  be  The l o s s o f  three a d u l t s f u r t h e r r e i n f o r c e s t h a t c o n c l u s i o n .  by p r e d a t o r s (Dusl and Dusi 1968, P r a t t  eagle  I  caused  concluded  that p r e d a t o r s were u n u s u a l l y s u c c e s s f u l i n the Pender Harbour colony and were p e r s i s t e n t a t v u l n e r a b l e n e s t s u n t i l a l l young were removed. Many o b s e r v a t i o n s have been made on the i n t e r a c t i o n s o f a v i a n and o t h e r p r e d a t o r s with herons and heron c o l o n i e s . Occupancy o f heron n e s t s by p r e d a t o r y b i r d s has been c i t e d as the cause o f colony abandonments both i n t h i s study ( C h e h a l i s , Crescent, Coquitlam and M c G i l l i v r a y c o l o n i e s ) and o t h e r s (Mark 1976, Vermeer 1973)•  In c o n t r a s t , g r e a t horned owls and  b a l d eagles have been r e c o r d e d as n e s t i n g i n o r near  10 d i f f e r -  ent h e r o n r i e s without causing abandonment (Vermeer 1972 1973, Bayer 1979, Koonz 1980) .  and  The Salwein colony had a p a i r  o f g r e a t horned owls n e s t i n g i n one o f the "heron" nests but  37 t h a t colony had a s u c c e s s f u l n e s t i n g season i n 1979•  Eagles  n e s t i n g near the Pender Harbour colony i n 1978 d i d not cause herons to abandon n e s t i n g . The v a r i a t i o n i n the e f f e c t s o f p r e d a t o r s on n e s t i n g success may  be due to d i f f e r e n c e s i n the r e l a t i o n s h i p s o f the  species i n d i f f e r e n t areas.  Both owls and eagles have been  r e p o r t e d to prey upon o r harass a d u l t and n e s t l i n g herons (Bayer 1979. Werschkul 1979. Krebs 1 9 7 ^ ) .  Crows, ravens  and  turkey v u l t u r e s (Cathartes aura) a l s o prey on young herons ( T a y l o r and M i c h a e l 1971, Temple 1969, Dusi and Dusi  1968),  but have never been suspected o f causing colony abandonment. I t may  be t h a t the i n t e n s i t y o f p r e d a t o r i n t e r a c t i o n s d e t e r -  mines the response o f a n e s t i n g colony.  Presumably i f p r e d a t i o n  causes s i g n i f i c a n t l o s s e s i n r e p r o d u c t i o n or a d u l t m o r t a l i t y i t would be to the advantage o f the herons to r e l o c a t e , p r o v i d e d that p r e d a t i o n i s reduced a t the new  location.  The abandonment  o f h e r o n r i e s a t U.B.C. i n 1979. and Pender Harbour i n I 9 8 O , suggests t h a t herons move to a new o l d s i t e exceed  15% (Table 1-5)  s i t e i f n e s t s l o s t at the  o r i f the number l e a v i n g a  colony exceeds the number e n t e r i n g d u r i n g the breeding  season.  The r e d u c t i o n o f nest l o s s e s i n the U.B.C. colony, f o l l o w i n g r e l o c a t i o n , may  have r e l a t e d to lower p r e d a t i o n at the  new  site. Observations o f eagle-heron t h a t herons may  i n t e r a c t i o n s i n 1980  show r a d i c a l l y d i f f e r e n t responses  suggested  to eagles  a t d i f f e r e n t l o c a t i o n s , p o s s i b l y r e l a t e d to the l e v e l o f p r e d a t i o n s u f f e r e d by the herons.  Feeding herons at Pender Harbour  38 r a r e l y allowed an eagle to approach w i t h i n 100 meters without f l e e i n g , whereas those a t S e c h e l t r e a c t e d o n l y by assuming an a l e r t posture even upon the c l o s e approach o f an eagle I98O).  Heron responses  to eagle harassment s i m i l a r to those  a t Pender Harbour are d e s c r i b e d by Bayer ( 1 9 7 9 ) . t i o n on both a d u l t and  j u v e n i l e herons was  Harbour but not a t S e c h e l t . that herons may  Reproductive  Eagle  preda-  observed a t Pender  Those o b s e r v a t i o n s a g a i n  a l t e r t h e i r response  a r e s u l t of previous  (Forbes  suggest  to c e r t a i n p r e d a t o r s as  experience.  Success  Reproductive  success was  assessed a t a l l c o l o n i e s u s i n g  the mean number f l e d g e d per s u c c e s s f u l nest (MYSN).  Although  the number o f young f l e d g e d per breeding p a i r (MYBP) i s a b e t t e r estimate o f heron p r o d u c t i v i t y , MYSN has been the standard used i n many p r e v i o u s r e p o r t s (see reviews by Parker I98O, Quinney and Smith 1979).  Our  f l e d g i n g r a t e s were s i m i l a r  to the r e s u l t s o f o t h e r s and few d i f f e r e n c e s were found among study c o l o n i e s u s i n g MYSN. Nest l o s s e s were the most important parameter determining the r e p r o d u c t i v e s t a t u s o f a colony. turbance a t Pender Harbour was  The  e f f e c t o f the d i s -  not r e f l e c t e d by MYSN.  S u c c e s s f u l p a i r s r a i s e d as many young as a d u l t s i n u n d i s t u r b e d c o l o n i e s ( F i g . 1-2).  Reproductive  i n c r e a s i n g the percentage  l o s s e s were r e f l e c t e d  of unsuccessful pairs  by  (Table 1-5).  Pender Harbour had p r o p o r t i o n a t e l y more u n s u c c e s s f u l nests six  o t h e r c o l o n i e s i n 1978  p < .001).  (Table 1-5. x  2  =  than  38.4., 1 d f ,  Pender Harbour a l s o had p r o p o r t i o n a t e l y more nest  39 f a i l u r e s than the S e c h e l t colony i n 1979  (Table 1-5,  1 d f , p < .01) o r the U.B.C. colony i n 1978 p  < .01).  (x  2  x  2  = 7.^9.  =  6.73,  1 df,  Those r e s u l t s show t h a t some a d u l t s l o s e a l l t h e i r  young under adverse  c o n d i t i o n s , while o t h e r s are u n a f f e c t e d .  At Pender Harbour i n 1978, at the nest were probably  t o l e r a n c e o f d i s t u r b a n c e and t e n a c i t y important  f a c t o r s determining  the  success or f a i l u r e o f d i f f e r e n t n e s t i n g p a i r s . Determining  nest abandonment r e q u i r e s repeat i n s p e c t i o n s  o f i n d i v i d u a l l y l a b e l l e d p l a t f o r m s a t each colony. t e d i o u s and time-consuming job and may  This i s a  represent a considerable  d i s t u r b a n c e to n e s t i n g herons i n non-urban c o l o n i e s . p o r t i o n o f p l a t f o r m s occupied estimate  The  i n each colony can be used to  the number o f nests abandoned, p a r t i c u l a r l y j u s t  to f l e d g i n g when p l a t f o r m occupancy i s g e n e r a l l y high The low p l a t f o r m occupancy a t Pender Harbour i n 1978 1979  (36$) was  probably  the adjacent housing  pro-  prior  (Table {27%)  1-7).  and  r e l a t e d to d i s t u r b a n c e from work i n  development.  Nest abandonment  p l a t f o r m occupancy while c o n s t r u c t i o n o f new  decreased  nests, further  from the d i s t u r b a n c e than e x i s t i n g p l a t f o r m s , i n c r e a s e d the number o f a p p a r e n t l y s u i t a b l e nest  sites.  P l a t f o r m occupancy can be used to estimate  the number  o f u n s u c c e s s f u l p a i r s a t each colony and p r o v i d e a more meani n g f u l index o f the p o p u l a t i o n and p r o d u c t i v i t y o f herons MYSN. first  For example, i f surveys had been undertaken f o r the time i n I 9 8 O , low p l a t f o r m occupancy a t Gibsons and  Coquitlam The  than  would have i n d i c a t e d s u b s t a n t i a l nest abandonment.  r e l a t i o n s h i p between p l a t f o r m occupancy and nests abandoned  40 ( F i g . 1-3)  can be used to estimate the number o f nest  failures  a t c o l o n i e s where there i s a l a r g e p r o p o r t i o n o f vacant  nests.  For colony s i t e s which are completely abandoned (e.g. Pender Harbour and U.B.C.) I would expect  to f i n d a l t e r n a t e n e s t i n g  sites. I t e s t e d t h i s r e l a t i o n s h i p u s i n g data c o l l e c t e d where by Des Granges and Laporte  (1981, 1983)  else-  and P a r k e r  (I98O).  I noted t h a t 33 small (<20 nests) c o l o n i e s f r e q u e n t l y had  no  u n s u c c e s s f u l n e s t s (15) o r were completely abandoned ( 2 ) . I excluded data from these c o l o n i e s .  I approximated nest  occupancy a t f l e d g i n g by s u b t r a c t i n g u n s u c c e s s f u l nests from the number r e p o r t e d to be occupied i n May F i g u r e 1-4 and  f o r each colony.  shows the r e l a t i o n s h i p o b t a i n e d u s i n g that data  the combined r e g r e s s i o n l i n e .  A n a l y s i s o f covariance  showed that the means o f r e s i d u a l s from the combined r e g r e s s i o n l i n e were the same f o r a l l s t u d i e s .  T h i s r e l a t i o n s h i p may  u s e f u l i n e s t i m a t i n g nest f a i l u r e s i n h e r o n r i e s i n o t h e r  be areas  which have low p l a t f o r m occupancy a t f l e d g i n g . At Pender Harbour and U.B.C, where the numbers o f nests abandoned exceeded those o f p l a t f o r m s o c c u p i e d d u r i n g the  breed-  i n g season i n 1978 o r 1979 % the c o l o n i e s were abandoned the f o l l o w i n g year.  I d i d not c o l l e c t data on n e s t abandonments  a t U.B.C. i n 1979 hut the 100 percent p l a t f o r m occupancy a t f l e d g i n g suggests  t h a t there were few abandonments and MYBP  i n c r e a s e d a t the new  location.  MYSN d i d not change f o l l o w i n g  colony s h i f t s a t U.B.C, Coquitlam (Fig.  1-2).  and M c G i l l i v r a y - S a l w e i n  S i n c e the number o f young r a i s e d per s u c c e s s f u l  41  QUEBEC, MONTANA  20  40  %  60  80  100  P L A T F O R M S O C C U P I E D A T F L E D G I N G  FIG. 1-4 The relationship between the percentage of nest platforms occupied at fledging and the percentage of unsuccessful pairs at colonies in Note:  Data from Parker  Quebec and Montana.  DesGranges 1981 and 1983  1980.  and  42 nest does not change when h e r o n r i e s are s e v e r e l y d i s t u r b e d o r r e l o c a t e , i t i s probably a poor i n d i c a t o r o f r e p r o d u c t i v e success.  Numbers o f s u c c e s s f u l and abandoned n e s t s , which  can be estimated u s i n g percent p l a t f o r m occupancy at f l e d g i n g , more a c c u r a t e l y r e p r e s e n t the r e p r o d u c t i v e success o f h e r o n r i e s .  CONCLUSIONS Frequent  heronry abandonments, changes'in  size,  and  r e l o c a t i o n s have r e s u l t e d i n c o n c e n t r a t i n g herons i n t o l a r g e r c o l o n i e s a t fewer l o c a t i o n s than were h i s t o r i c a l l y present i n the lower mainland.  Many o f these changes may  by urban development.  have been caused  Sudden l a r g e changes i n colony  sizes  between years probably r e s u l t from movement o f a d u l t s between colonies.  The  frequent, and  i n some -cases  voked, movements o f heron c o l o n i e s suggest may  a p p a r e n t l y unprot h a t such  r e p r e s e n t a normal p a r t o f a heron's l i f e  occurrences  cycle.  Human d i s t u r b a n c e a t c o l o n i e s unaccustomed to  people  i n c r e a s e s p r e d a t i o n , s i n c e a d u l t s are e a s i l y f r i g h t e n e d from t h e i r nests.  H e r o n r i e s which have adapted to human a c t i v i t y  s u f f e r l e s s p r e d a t i o n s i n c e b i r d s do not r e a d i l y f l u s h from t h e i r n e s t s , and p r e d a t o r s may  be i n h i b i t e d by human a c t i v i t i e s .  Some nest p r e d a t i o n occurs i n most h e r o n r i e s , but  disturbances  which f r i g h t e n a d u l t s from t h e i r nests i n c r e a s e l o s s e s o f eggs and young and reduce the number o f s u c c e s s f u l n e s t s . p r e d a t i o n continued a t one turbance  stopped.  Heavy  colony a f t e r a c o n s t r u c t i o n d i s -  Responses o f herons to p r e d a t o r s v a r i e d  4-3 i n r e l a t i o n to the s e v e r i t y o f p r e d a t i o n .  When l a r g e numbers  o f young or a d u l t s are l o s t , h e r o n r i e s r e l o c a t e . The number o f young f l e d g e d per s u c c e s s f u l p a i r i s an i n s e n s i t i v e measure o f r e p r o d u c t i v e success. between c o l o n i e s even when a colony was Disturbance  I t d i d not  vary  severely disturbed.  a f f e c t e d r e p r o d u c t i o n by i n c r e a s i n g the number o f  unsuccessful p a i r s .  The number o f u n s u c c e s s f u l p a i r s cannot  be estimated by nest counts a t two  p e r i o d s because nest a d d i -  t i o n s u s u a l l y exceed nest l o s s e s w i t h i n a colony.  To a v o i d  the need to l a b e l i n d i v i d u a l nests and do repeat counts, percent of n e s t s abandoned can be estimated o f p l a t f o r m s occupied at f l e d g i n g .  from the  the  percent  T h i s method i s a p p l i c a b l e  i n o t h e r a r e a s , at l e a s t f o r l a r g e r h e r o n r i e s  (>20  nests).  Nest l o s s e s , which can be estimated u s i n g p l a t f o r m occupancy a t f l e d g i n g , are more important  than the numbers o f young  f l e d g e d per s u c c e s s f u l p a i r i n a s s e s s i n g heron r e p r o d u c t i v e success and p o p u l a t i o n s t a t u s .  44  CHAPTER I I  Movements, Behavior and Breeding Succe o f Banded Herons a t Pender Harbour  45 INTRODUCTION R e s u l t s i n Chapter I showed t h a t c h a r a c t e r i s t i c s o f breeding b i r d s , such as nest t e n a c i t y , were important r e p r o d u c t i v e success.  to  S t u d i e s o f another c o l o n i a l b i r d have  shown that s e l e c t i n g the same colony, mate and nest s i t e each year i s a s s o c i a t e d with i n c r e a s e d breeding success and Thomas 1983).  (Coulson  Other c h a r a c t e r i s t i c s o f p a r e n t s , such as  f e e d i n g areas used, f e e d i n g success and s o c i a l dominance, might a l s o i n f l u e n c e r e p r o d u c t i o n , but no Information e x i s t s f o r herons because i n d i v i d u a l s have not p r e v i o u s l y been r e l i a b l y i d e n t i f i e d i n c o l o n i e s o r on f e e d i n g areas  (Quinney  and Smith 1979, Mock 1976, McAloney 1973. P r a t t 1972 and Henny and Bethers  1971).  1970,  Marked b i r d s would a l s o confirm the  movements o f herons between c o l o n i e s , f o r which there i s cons i d e r a b l e c i r c u m s t a n t i a l evidence One  (Chapter I ) .  o f the p r i n c i p a l t h e o r i e s attempting  to e x p l a i n  c o l o n i a l n e s t i n g suggests t h a t c o l o n i e s a c t as i n f o r m a t i o n centers f o r food f i n d i n g (Custer and Osborn 1978, Ward and Zahavi 1973)•  T h i s theory proposes  t h a t adjacent  individuals  w i t h i n c o l o n i e s f o l l o w each o t h e r to good f e e d i n g s i t e s . Krebs (1974) and Des Granges (1978) showed t h a t a r r i v a l  and  departure f r e q u e n c i e s and f l i g h t d i r e c t i o n s o f herons at c o l o n i e s were s i g n i f i c a n t l y clumped, suggesting t h a t b i r d s were t r a v e l l i n g together to and from f e e d i n g a r e a s .  More  recent s t u d i e s , based on the movements o f a d u l t s to and h e r o n r i e s , have shown t h a t many herons have predetermined  from feed-  i n g areas or join aggregations of f e e d i n g b i r d s adjacent to the  46 colony  (Pratt  1980)  and  t h a t departure  i s r e l a t e d to the time o f low  tide  and a r r i v a l  (Bayer  I98I).  i d e n t i f i a b l e i n d i v i d u a l s w i t h i n h e r o n r i e s has  clumping The  l a c k of  prevented  the  d i r e c t t e s t i n g o f the i n f o r m a t i o n exchange h y p o t h e s i s . More g e n e r a l s t u d i e s have r e l a t e d f e e d i n g s i t e s to heron colony l o c a t i o n s .  Most l a r g e r h e r o n r i e s are l o c a t e d w i t h i n  10 k i l o m e t e r s o f p r o d u c t i v e marshland o r t i d a l f e e d i n g  areas,  and most b r e e d i n g herons have r e l a t i v e l y p r e d i c t a b l e f e e d i n g areas  (Thompson 1 9 7 9 a ,  Some breeding areas and 1979b).  Werschkul et a l . 1 9 7 7 .  herons, however, do not use  1973).  Vermeer  the c l o s e s t  feeding  t r a v e l much f u r t h e r to f e e d (Parr i s and Grau 1979. Thompson Some r e s e a r c h e r s have observed t h a t many g r e a t  herons have f e e d i n g s i t e s which they defend ( P r a t t  1980, P i e f e r 1979.  frequent and  Hedeen 1 9 6 7 ) .  blue  sometimes  Feeding  terri-  t o r y defence i s most pronounced i n w i n t e r when herons have d i s p e r s e d from the breeding are l a r g e and obvious.  exclusive t e r r i t o r i e s  In c o n t r a s t , the l a r g e f e e d i n g  observed i n summer, suggest Some r e p o r t s suggest  c o l o n i e s and  t h a t herons are not  Bayer ( 1 9 7 8 )  (Bayer  a l s o suggested that the  m o r t a l i t y ' f o r young herons over w i n t e r from t h e i r e x c l u s i o n from w i n t e r nant t e r r i t o r i a l a d u l t s .  seasonal  t i d a l h a b i t a t s which, because o f  l i m i t e d a v a i l a b i l i t y , are not worth defending Stingle 1978).  territorial.  t h a t communal f e e d i n g occurs a t  prey c o n c e n t r a t i o n s and  flocks,  (Henny 1 9 7 2 )  their  1978, greater may  result  f e e d i n g areas by more domi-  Although f e e d i n g a r e a  information  exchange c o u l d p o t e n t i a l l y be u s e f u l to c o l o n i a l b i r d s , the  47 need f o r such a mechanism among herons, many o f which have s p e c i f i c f e e d i n g s i t e s or t e r r i t o r i e s , i s q u e s t i o n a b l e . In o r d e r to o b t a i n i n f o r m a t i o n on mate s e l e c t i o n ,  feeding  areas and movements, I banded 60 percent o f the a d u l t herons a t the Pender Harbour colony  (Simpson and K e l s a l l  1979).  I compared the r e p r o d u c t i v e success o f banded i n d i v i d u a l s to t h e i r f e e d i n g success; movements; and I was  f e e d i n g , mate and nest s i t e  s o c i a l dominance.  selection;  Using data from banded b i r d s  able to assess the r e s u l t s and  c o n c l u s i o n s o f others  who  have used l e s s d i r e c t methods to study g r e a t blue herons.  METHODS A d u l t herons were captured i n net-covered  box  traps l o c a t -  ed on top o f the b a i t tanks a t three s i t e s i n Pender Harbour (Simpson and K e l s a l l  1979)  ( P i g . 2-1).  Each b i r d was  with a number-coded r e d p l a s t i c l e g band (Sladen 1978) c o n v e n t i o n a l aluminum band on the l e f t a n k l e .  marked and  a  The numbered l e g  band allowed p o s i t i v e i d e n t i f i c a t i o n o f i n d i v i d u a l s a t d i s t a n c e s up to 200 meters.  The  sex o f each banded heron was  from morphological  characteristics  (Appendix I ) .  were i d e n t i f i e d i n the n e s t i n g colony, on two  determined  Banded b i r d s  tidal  feeding  areas and a t three t r a p s i t e s w i t h i n Pender Harbour ( F i g . 2-1) d u r i n g the summers o f 1978, 1980).  1979 and  1980  ( K e l s a l l and  Simpson  S i g h t i n g s and r e c o v e r i e s o f dead b i r d s w i t h i n Pender  Harbour and  from surrounding  areas were a l s o r e c o r d e d .  Most  OD  FIG. 2-1 Locations of traps, observation blinds and seining sites at Pender Harbour.  49 s i g h t i n g s were a t the b a i t tanks and t i d a l f e e d i n g areas d u r i n g May, June and J u l y 1979. I d e f i n e d a nest p l a t f o r m as an o c c u p i e d nest o r a s t r u c t u r e which had o b v i o u s l y been a nest i n the p a s t .  The l o c a t i o n s  of p l a t f o r m s i n the colony were p l o t t e d by measuring the d i s tances and t a k i n g compass bearings between l i t t e r and dropping marks under each.  A l l t r e e s c o n t a i n i n g p l a t f o r m s were numbered  and the band numbers o f herons occupying each nest recorded i n 1978 and 1979.  The geometric  c e n t e r o f the colony was d e t e r -  mined by t a k i n g the mean X-coordinate and mean Y-coordinate o f occupied p l a t f o r m s i n each year.  The d i s t a n c e o f each p l a t f o r m  from the c o l o n y c e n t e r was then c a l c u l a t e d f o r 1978 and 1979 by simple a l g e b r a . In  1979 I v i s u a l l y s u b d i v i d e d the colony i n t o three  s e c t o r s — n o r t h , e a s t and west.  The n o r t h  sector•_ c o n t a i n e d  18 occupied n e s t s and 16 banded b i r d s ; the e a s t , 15 n e s t s and 15 banded b i r d s ; and the west, 12 n e s t s and 13 banded b i r d s . Each banded b i r d seen i n the colony was then r e l a t e d to a nest s i t e , a n e s t d i s t a n c e from c e n t e r measure and a s e c t o r w i t h i n which i t s n e a r e s t neighbors were l o c a t e d . Feeding r a t e s o f herons on two t i d a l f e e d i n g areas were determined  u s i n g t e l e s c o p e s from b l i n d s l o c a t e d on the shore  from A p r i l t o August 1979 ( F i g . 2 - 1 ) .  Observers  recorded the  s i z e and s p e c i e s o f each prey item d u r i n g m a n i p u l a t i o n by herons p r i o r to swallowing.  The l e n g t h o f each item was e s t i -  mated by comparison with the b i l l l e n g t h o f the heron 1974).  (Krebs  I e s t a b l i s h e d the weight-length r e l a t i o n s h i p f o r each  50 prey s p e c i e s by measuring f i s h captured u s i n g a beach i n O y s t e r Bay.  seine  The biomass caught by herons during each  10-minute o b s e r v a t i o n p e r i o d was  e s t i m a t e d by c o n v e r t i n g  each f i s h - l e n g t h to a weight and summing a l l weights.  Eleven  r e p l i c a t e t r i a l s showed t h a t biomass estimates d i d not d i f f e r s i g n i f i c a n t l y f o r three d i f f e r e n t o b s e r v e r s c o n c u r r e n t l y r e c o r d i n g i n f o r m a t i o n on the same heron ( F 2 p > .92).  t  30 = »0?6,  The average weight o f prey caught over s e v e r a l  t r i a l s was used f o r comparison o f i n d i v i d u a l s and groups o f i n d i v i d u a l s using a n a l y s i s o f variance.  Other f a c t o r s thought  to a f f e c t f e e d i n g r a t e were a l s o r e c o r d e d f o r each trial,  10-minute  I n c l u d i n g t i d e d i r e c t i o n and l e v e l , s u b s t r a t e , water  depth and date. I a l s o observed herons f e e d i n g a t n i g h t on b a i t tanks from A p r i l to J u l y 1979* and t h i s was  Most b a i t tanks had overhead l i g h t i n g ,  supplemented by s p o t l i g h t s mounted a t l e g l e v e l  to make band numbers r e a d a b l e .  S i z e estimates o f h e r r i n g  caught were u n r e l i a b l e because a l l h e r r i n g were l o n g e r than a herons's b i l l .  I e s t i m a t e d the t o t a l weight o f f i s h caught  i n 10 minutes by m u l t i p l y i n g the number caught by the mean weight o f samples o f f i s h taken from the b a i t tanks i n A p r i l and J u l y . I e s t a b l i s h e d n i n e seine s i t e s i n Oyster Bay i n March (Fig. 2-1).  1979  S i x o f those s i t e s were used c o n s i s t e n t l y from  March through September.  Wooden stakes were used as markers  and as anchors f o r the net d u r i n g s e i n i n g .  Each s i t e  was  s e i n e d on the ebb and f l o o d t i d e f o r a t l e a s t three c o n s e c u t i v e  51 days each month.  The number and s p e c i e s o f f i s h captured a t  each s i t e were r e c o r d e d .  Specimens were taken to confirm  i d e n t i f i c a t i o n o f each s p e c i e s and a sample o f each s p e c i e s was weighed and measured to determine t h e i r mean weight and l e n g t h each month.  The change i n prey biomass per month was  estimated by adding the t o t a l weight caught f o r each s p e c i e s (number caught x mean weight) f o r a l l abundance was  seine s i t e s .  Prey  then expressed as a mean weight caught per s e t  each month. The dominance and a g g r e s s i v e n e s s o f some banded  herons  were determined by r e c o r d i n g i n t e r a c t i o n s between herons on feeding areas.  The r e t r e a t i n g b i r d was  deemed the l o s e r .  In cases where there was no c l e a r winner the i n t e r a c t i o n called a tie.  was  Herons with the g r e a t e s t p r o p o r t i o n o f wins  were g i v e n the h i g h e s t rank f o r dominance;  those w i t h the  g r e a t e s t number o f i n t e r a c t i o n s were g i v e n the h i g h e s t rank for  interactions. For most banded herons the number o f young  determined by counts made i n the c o l o n y .  fledged  was  I had r e p r o d u c t i v e  i n f o r m a t i o n f o r both 1978 and 1979 f o r 14 banded herons. Reproductive data from 1979 was used f o r comparison w i t h colony, s i g h t i n g , f e e d i n g r a t e and s o c i a l i n t e r a c t i o n d a t a , most o f which was  a l s o c o l l e c t e d i n 1979.  52 RESULTS Capture and Banding We captured a t o t a l o f 79 d i f f e r e n t h e r o n s — 6 8 i n 1978 (Simpson and K e l s a l l 1979) and 11 i n 1979*  During June 1979  an average o f 14 b i r d s were counted i n Oyster Bay and 26 i n K l e i n Bay each day ( F i g . 2-1).  The p r o p o r t i o n o f banded  herons  f e e d i n g i n those bays was 54 ± 3% (95% C I . ) i n 1978 and 53 ± 6% i n 1979.  I e s t i m a t e d that about 125 b i r d s used the Pender  Harbour a r e a each year, based on the r a t i o o f banded to unhanded birds.  I n 1979» counts o f the p r o p o r t i o n o f b i r d s banded were  a l s o made i n the n e s t i n g colony (60%) and on the b a i t tanks (62 ±  11%).  R e s i g h t i n g s and Movements o f Banded Herons A l l but three banded b i r d s were r e s i g h t e d a t l e a s t  once.  R e s i g h t i n g s averaged 21 times p e r b i r d with a maximum o f 61 sightings.  F i v e banded herons moved the 24 km between S e c h e l t  and Pender Harbour from 1978 to 1 9 8 0 .  One i n d i v i d u a l  (band  number A84) moved from Pender to S e c h e l t and back w i t h i n 13 days w h i l e another (A82) moved from S e c h e l t to Pender to S e c r e t Cove, 11 km south, w i t h i n 33 days.  Two i n d i v i d u a l s , each s i g h t e d  11 times a t Pender i n June and J u l y 1 9 7 9 , were seen a t S e c h e l t i n J u l y 1979 o r May I 9 8 O . seen a t Pender Harbour  One i n d i v i d u a l  (banded i n June 1978) but was s i g h t e d  twice a t S e c h e l t i n both 1979 and I 9 8 O . was  ( A 4 3 ) was never a g a i n  Another heron (A48)  seen a t Pender Harbour i n both 1978 and 1 9 8 0 , but not i n  1979.  F o r t y - e i g h t banded herons seen a t the Pender  Harbour  colony i n 1978 o r 1979 and a l i v e i n 1979 averaged 2 5 s i g h t i n g s each.  E i g h t e e n o t h e r s , not seen a t the colony, averaged 12  s i g h t i n g s each.  Two o f those herons (A94 and A 5 7 )  53 were seen 50 and 42  times r e s p e c t i v e l y and,  although they were  never i d e n t i f i e d i n the colony, I suspect that they were  two  o f f o u r u n i d e n t i f i e d banded herons n e s t i n g a t Pender Harbour in  1979.  Feeding Areas and N e s t i n g Status o f Banded Herons I c l a s s i f i e d a l l banded b i r d s as l o c a l f e e d i n g or d i s t a n t f e e d i n g , based on the number o f s i g h t i n g s a t Pender Harbour from 1 9 7 8  to I 9 8 O .  Herons with 15 or fewer s i g h t i n g s at  Pender Harbour were c l a s s e d as d i s t a n t f e e d i n g and  those over 15 as l o c a l f e e d i n g  (LF)  (DF)  birds  (Fig. 2 - 2 ) .  I also  c l a s s e d 48 banded herons seen a t the colony i n 1 9 7 8 as colony b i r d s , and  18 not  or  1979  seen, as non-colony b i r d s .  Overall  there were 36 colony LF b i r d s , f i v e non-colony LF b i r d s , 12  colony DF b i r d s and  In 1 9 7 8 ,  75%  (N = 2 1 )  (N = 44)  i n 1979.  13 non-colony DF b i r d s  not  2-1).  o f the colony b i r d s were LF, and  81$  were  For both years combined, LF b i r d s had more  s u c c e s s f u l n e s t s than DF b i r d s d i f f e r e n c e was  (Table  (Table 2 - 2 ) , although  the  s i g n i f i c a n t f o r e i t h e r year a l o n e .  DF  herons i n s u c c e s s f u l nests r a i s e d as many young as LF herons i n both y e a r s .  I examined the  s i g h t i n g records  o f a l l unsuc-  c e s s f u l DF herons to determine i f they were c l a s s e d as DF  birds  because they l e f t Pender Harbour or f e d l e s s o f t e n a f t e r l o s i n g t h e i r young.  Only one  i n d i v i d u a l (A55, Table 2-3)  had  signifi-  c a n t l y fewer s i g h t i n g s a f t e r l o s i n g i t s n e s t l i n g s compared to s i g h t i n g s f o r s u c c e s s f u l DF b i r d s . young l a t e i n the n e s t i n g were m i s c l a s s i f l e d .  Most DF herons l o s t  season so i t i s u n l i k e l y t h a t  their they  54  DF—I  0  5  LF  10 15 2 0 25 3 0 35 4 0 4 5 5 0 55  NO. OF S I G H T I N G S FIG. 2 - 2  Frequency distribution of the number of sightings  of 41 local feeding ( L F ) and 2 5 distant feeding (DF) banded herons at Pender Harbour.  Table 2 - 1 .  Number o f s i g h t i n g s o f banded herons a t Pender Harbour from 1978 to 1980 c a t e g o r i z e d by frequency o f o b s e r v a t i o n , s i g h t i n g l o c a t i o n and presence i n the colony. L o c a l feeding (>15 s i g h t i n g s ) Non-colony Colony (not a t (seen a t colony) colony)  Distant feeding (<15 s i g h t i n g s ) Colony Non-colony  12  13  137  37  29  21  38  35  No. o f banded b i r d s  36  5  No. o f s i g h t i n g s on tide f l a t s  797  No. o f s i g h t i n g s on b a i t tanks  316  1  2  1.  Includes  A 94 and A57 suspected colony  b i r d s — s e e• t e x t .  2.  Includes  f i v e seen a t S e c h e l t and one  recovered May 1979 on Texada I s l a n d .  Note:  With one noted exception i n c l u d e s only b i r d s known to be a l i v e i n June 1979 o r l a t e r and f o r which feeding s t a t u s was known.  Table 2 - 2 .  Comparison o f the r e p r o d u c t i v e success o f l o c a l f e e d i n g (LF) and d i s t a n t f e e d i n g (DF) herons a t Pender Harbour i n I 9 7 8 and 1979. No. successful  1978  1979  1978  and 1979  Note:  LF DF LF DF  13 3  27 3  MYSN  SD  No. unsuccessful  1.8  .73  2  2.7  .58  2  3.0  .76  7  2.7  .58  5  LF  40  9  DF  6  7  Three herons f o r which LF or DF s t a t u s was undetermined questionable ( A 5 5 , Table 1 6 ) , not i n c l u d e d .  x  2  P  I.67  >  .10  3.65  •y  .05  6.75  <  .01  (A68,  A76)  or  Table 2-3.  Bird  A21 SDF  A27  Comparison o f the number o f s i g h t i n g s o f d i s t a n t f e e d i n g (DF) herons to determine i f u n s u c c e s s f u l b i r d s were seen l e s s o f t e n than s u c c e s s f u l b i r d s a f t e r t h e i r young were l o s t .  S i g h t i n g s before date young l o s t 0  17  4  SDF  22  A38 SDF  0  A46 SDF  Date young l o s t June 19 June 24 May 20  5 5  June 24  2  June 16  22  A 54 SDF  17  A55 SDF  5 5  May 20  Sightings a f t e r date young l o s t  3  X  2  P  1.95  < .1  0.03  < .8  37  1.89  < .1  0 20  2.35  < .1  14  3  20  0  0  25  2.76  .05  4 37  6.17  < .02  58 Nest S i t e s , Mates and Feeding Areas o f Banded Herons Twenty-one banded b i r d s were i d e n t i f i e d on nests i n the colony i n 1978 and 44 i n 1979 banded p a i r s .  i n c l u d i n g , f o r both y e a r s ,  18  In 1978, I I d e n t i f i e d f i v e p a i r s where both  mates were banded. together i n 1979•  None o f these p a i r s d e f i n i t e l y remained Seven o f the b i r d s were i d e n t i f i e d with  d i f f e r e n t mates i n 1979. two were not seen i n the colony  and  one was  21  p a i r e d with an u n i d e n t i f i e d banded b i r d .  herons i d e n t i f i e d on nests i n 1978,  Of the  13 were on d i f f e r e n t  nests  i n 1979. one on the same nest and seven were not seen i n the colony.  I d i d not observe  w i t h i n one n e s t i n g season. o r young i n 1979•  any a d u l t s moving between n e s t s E i g h t p a i r s l o s t a l l t h e i r eggs  None o f the 13 banded b i r d s i n v o l v e d i n  these p a i r s attempted to r e n e s t i n the Pender Harbour colony i n 1979. although  I d i d observe  two  u n s u c c e s s f u l attempts at  l a t e n e s t i n g by unbanded i n d i v i d u a l s . S u c c e s s f u l nests were much c l o s e r to the c e n t e r o f the colony than u n s u c c e s s f u l nests i n 1978. there was  little  In 1979. however,  d i f f e r e n c e between these groups (Table 2 - 4 ) .  The mean d i s t a n c e o f a l l occupied nests from the colony was  about 30 meters i n both  center  years.  I examined nest p o s i t i o n and f e e d i n g l o c a t i o n s o f banded herons to determine i f banded herons n e s t i n g c l o s e together a l s o f e d i n the same areas i n Pender Harbour.  Herons t h a t  nested i n the same s e c t o r o f the colony d i d not feed i n the same a r e a s .  In f a c t , herons from each s e c t o r o f the  colony  were u n i f o r m l y d i s t r i b u t e d among the f o u r p r i n c i p a l f e e d i n g areas i n Pender Harbour (Table 2 - 5 ) .  59 Table 2-4.  Mean d i s t a n c e s (m) o f s u c c e s s f u l and u n s u c c e s s f u l n e s t s from the center o f the colony i n 1978 and 1979 a t Pender Harbour. Successful  1I  Unsuccessful  SE  N  X  SE  N  Median test  1978  24.1  I.96  25  42.5  4.41  14  p <.001  1979  29 .4  I.71  33  31.6  3.36  12  p  Table 2-5.  <.56  T o t a l number o f banded herons from each s e c t o r o f the Pender Harbour colony seen f e e d i n g together on f o u r d i f f e r e n t days i n 1979.  Feeding location  Number o f herons from each s e c t o r North  East  West  K l e i n Bay  10  21  15  Oyster Bay  18  11  13  Trap 1  18  15  15  Trap 2  9  8  9  I a l s o examined  X  6.05  (P > .3)  the f e e d i n g l o c a t i o n s o f banded p a i r s i n  1979 to t e s t i f the male and female tended to use the same f o r a g i n g zone.  In e i g h t o f the 11 p a i r s , the male and female  d i f f e r e d s i g n i f i c a n t l y i n t h e i r frequency o f s i g h t i n g s a t f i v e d i f f e r e n t f e e d i n g l o c a t i o n s (Table 2 - 6 ) .  One member o f each  of the three p a i r s which d i d not d i f f e r s i g n i f i c a n t l y had few s i g h t i n g s , making a v a l i d comparison d i f f i c u l t . o f banded p a i r s , which f e d mostly w i t h i n Pender t h e r e f o r e used d i f f e r e n t f e e d i n g areas i n 1979.  The members Harbour,  6o  Table 2-6.  The number o f s i g h t i n g s f o r each member o f 11 banded p a i r s a t f i v e f e e d i n g l o c a t i o n s i n Pender Harbour i n 1979.  Banded Feeding pair status K l e i n  Feeding l o c a t i o n s X  Oyster  Tl  T2  2  df •  T3.  P  A26 A37  LF LF  18 15  0 •5  11 3  0 0  • 0 0  6.1  2  A65 A35  LF LF  16 3  0 21  0 1  0 0  0 0  26.4  1  <  A33 A21  LF  6 2  11 1  2 0  0 0  0 0  1.4  1  > .05  A 54 A93  DF LF  1 28  1 1  0 1  0 1  0 1  2.1  1  >  .05  A59 A7l  LF LF  24 39  13 8  13 0  6 0  0 2  19.5  3  <  .05  A63 A90  LF DF  21 6  2 1  0 0  4 1  0 0  0.2  1  >  .05  A70 A 64  LF LF  18 0  5 8  7 6  0 0  1 0  14.6  2  <  .05  A78 A77  LF LF  20 1  3 16  4 10  0 0;  2  1,  24.8  3  <  .05  A86 A 79  LF LF  11 2  11 18  2 11  0 0  1 0  12.0  2  <  .05  A95 A66  LF LF  4 26  22 2  15 10  1 1  0 0  33.7  2  <  .05  A99 A56  LF LF  12 6  1 17  0 12  7 0  0 1  14.6  3  <  .05  Note:  ?  Includes o n l y p a i r s with 220 s i g h t i n g s i n 1979 c a t e g o r i e s combined i f e x p e c t e d s < l .  and  .05 .05  61 Feeding on T i d a l Areas We completed 907 10-minute f e e d i n g t r i a l s from A p r i l to August 1979.  S e v e r a l environmental  r a t e s o f the herons (Table 2 - 7 ) .  f a c t o r s influenced feeding  Most o f those  factors r e f l e c t  i n d i v i d u a l choice and c o u l d be considered i n h e r e n t i n the f e e d ing rates of d i f f e r e n t i n d i v i d u a l s .  Herons captured more prey  on e b b t i d e s , and i n deeper water (Table 2 - 7 ) .  The b i g g e s t  source o f v a r i a b i l i t y i n f e e d i n g r a t e s , however, was the change i n prey abundance with time.  The mean weight o f prey caught  per feeding t r i a l and prey abundance, estimated sampling,  from seine  i n c r e a s e d from A p r i l to June then decreased  and August ( F i g . 2-3) . J u l y and August.  i n July  Catch r a t e s d i d not d i f f e r between May,  I compared the catch r a t e s o f banded herons  which s u c c e s s f u l l y r a i s e d young with those  that f a i l e d i n 1979.  Catch r a t e s d i d not d i f f e r d u r i n g June o r d u r i n g the combined May, J u l y , August p e r i o d (Table 2-8).  I a l s o compared the prey  capture r a t e s between s u c c e s s f u l herons, which r a i s e d from one to f i v e young, to determine i f b i r d s which f l e d g e d more young had h i g h e r prey capture r a t e s .  There was no r e l a t i o n s h i p  between the f e e d i n g r a t e s o f the parents and the number o f young r a i s e d  ( F 3 , I+QJ  = 1«5, P > .22).  Other data a l s o sug-  gested t h a t food a v a i l a b i l i t y and catch r a t e s o f herons d i d not l i m i t the r e p r o d u c t i v e success o f herons a t Pender Harbour. A s i n g l e female s u c c e s s f u l l y r a i s e d two young a f t e r h e r mate d i e d on June 9, 1979.  Despite the f a c t t h a t the maximum food  demand o f young b i r d s occurs i n l a t e June, j u s t p r i o r to f l e d g i n g , t h i s s i n g l e female was a b l e to supply the needs o f her young.  62 Table 2-7.  Factor  F a c t o r s a f f e c t i n g the weight (gm) herons on t i d a l f e e d i n g a r e a s .  Level  f o ^ i n ? ^ !  S D  o f -prey caught by  F  N  Signif.  Tide direction  Ebb Flood  13.86  10.5 12.3  556 336  9.4  .002  Location  Klein Oyster  13.09 11.71  11.7  539 309  3.1  .079  Water depth  Dry Ankle < knee > knee Feather  5.19 11.95 12.60 12.31 17.55  3.4  9 161 378 211 7.7  .000  Algae Eelgrass Marsh Mud Oysters Rock  12.58  7.6  .000  Bottom substrate  Grand mean  11.48  9.4  11.1 9.9 9.6 16.2  148  20 717  8.30 10.33 2.19  5.8 11.6 16.1 9.5 11.9 2.1  13.15  total  907  14.26 14.17  4 147  16 3  63  FIG. 2-3 Correlation between prey caught by herons ( N • 907) and prey caught by seining (N = 2 4 4 ) for five months in 1979.  64 Table 2-8. Comparison o f the weight of. prey caught by herons which s u c c e s s f u l l y r a i s e d young and those that f a i l e d to r a i s e young i n 1979.  T i  P  * „  du?t i°ve * ; ^ status -  e  r  e r l o d  w t  1 0  c  m i n  a  f  c  r  l  t  / a  l  SD  N  F  70  June  Successful Failed  16.47 13.01  9.9 5.9  24  May, J u l y , August  Successful Failed  13.49 14.98  8.1 10.0  182 38  Signif.  2.6  .110  1.0  .319  Feeding at the B a i t Tanks O b s e r v a t i o n s o f herons f e e d i n g on the b a i t tanks i n A p r i l (N = 15) and June (N = 6) showed that catch r a t e s were much higher  (392 ± 64 and  t i d a l areas (2.97 ±  186 ± 22 g, r e s p e c t i v e l y ) than on .33. N = 54 and  p e c t i v e l y ) f o r 10-minute feeding tanks f r e q u e n t l y captured two strike.  I saw  them a p p a r e n t l y  two  16.18  trials.  ±  natural  .79, N = 314,  res-  Herons at the b a i t  o r three h e r r i n g i n a s i n g l e  herons c a p t u r i n g h e r r i n g then r e l e a s i n g  a f t e r t h e i r hunger was  satiated.  Feeding  success o f herons on the b a i t tanks v a r i e d g r e a t l y depending on the number and b e h a v i o r o f f i s h i n the tank.  The  d i d provide  source f o r  an e x t r a o r d i n a r y  and  a t t r a c t i v e food  b a i t tanks  herons a t Pender Harbour. Aggressive  Interactions  Most a g g r e s s i v e  i n t e r a c t i o n s (82 percent) o c c u r r e d  on  the  b a i t tanks because o f the crowding o f b i r d s competing f o r favorable  feeding s i t e s .  Forty-nine  evening counts made from  65 mid-June to mid-July 1979 on two b a i t ponds showed a mean o f herons with a maximum o f 2b and a minimum o f s i x b i r d s  10.5 using on  each pond.  tidal  feeding  Other i n t e r a c t i o n s areas during  feeding  (18 percent) were r e c o r d e d trial  observations.  I r e c o r d e d 572 a g g r e s s i v e i n t e r a c t i o n s i n v o l v i n g 51 banded herons i n 1979.  Although the average was 11.2 i n t e r a c t i o n s  per b i r d , the d i s t r i b u t i o n was skewed r i g h t , s o herons were i n v o l v e d a l s o able  that only  i n more than 10 i n t e r a c t i o n s .  16  I was  to c l a s s i f y 38 o f those 51 b i r d s as s u c c e s s f u l o r  unsuccessful  b r e e d i n g and l o c a l  (LF) o r d i s t a n t f e e d i n g  (DF)  i n 1979. Successful  LF herons c o n s i s t e n t l y won more a g g r e s s i v e  i n t e r a c t i o n s than f a i l i n g DF herons, but there were few f a l l i n g b i r d s o f known status and the d i f f e r e n c e was not significant  (Table  2-9).  Successful  and LF b i r d s were  i n more encounters than f a l l i n g o r DF herons (Table Differences  2-10) .  i n numbers o f i n t e r a c t i o n s f o r DF and LF b i r d s  p r o b a b l y r e l a t e to t h e i r d i f f e r i n g frequency o f at  involved  s i t e s where i n t e r a c t i o n s were r e c o r d e d .  observation  F o r LF b i r d s ,  the lower number o f i n t e r a c t i o n s f o r f a i l i n g herons may r e l a t e to t h e i r avoidance o f c o n f r o n t a t i o n s  with o t h e r b i r d s .  found no r e l a t i o n s h i p between the d i s t a n c e  I  o f a nest from the  colony c e n t e r o r the number o f young r a i s e d and the dominance or i n t e r a c t i o n rank o f the p a r e n t s .  66 Table 2-9.  Comparison o f the dominance o f banded herons with d i f f e r e n t r e p r o d u c t i v e success and f e e d i n g areas a t Fender Harbour i n 1979. Local/ distant feeding  N  x % wins  KruskalW a l l i s H.  Signif.  LF DF  38 13  45.6 30.2  2.13  0.14  Succ. Fail.  LF LF  27 6  47.2 23.8  2.59  0.11  Succ. Fail.  DF DF  3 2  18.6 50.0  0.08  0.77  ColonyColony  LF DF  33 5  42.9  31.1  0.67  0.41  Succ. Fail.  —  30 8  44.3 30.4  0.74  0.39  Reprod. status  —  Table 2- 10.  Comparison o f the t o t a l number o f a g g r e s s i v e i n t e r a c t i o n s f o r banded herons i n r e l a t i o n to r e p r o d u c t i v e success and f e e d i n g areas a t Pender Harbour i n 1979. J  Local/ distant feeding  N  x no. interactions  KruskalW a l l i s H.  Signif.  LF DF  38 13  13-2 5.5  5.76  0.02  Succ. Fail.  LF LF  27 6  15.8 4.2  6.47  0.01  Succ. Fail.  DF DF  3 2  7.3 1.0  1.33  0.25  Colony Colony  LF DF  33 5  13.7 4.8  3.21  0.07  30 8  15.0 3.4  9.15  0.01  Reprod. status  Succ. Fail.  —  67 Table 2-11.  Changes i n r e p r o d u c t i v e success f o r e i g h t males and s i x females from 1978 to 1979. Reproductive status  1978  1979  Males  Fail. Succ.  1 7  1 7  Females  Fail. Succ.  0 6  3 3  Sex and Reproductive Success A l l 79 captured herons were sexed u s i n g the d i s c r i m i n a n t f u n c t i o n shown i n Appendix males and 37 females.  I.  The banded group i n c l u d e d 42  For herons not n e s t i n g a t Pender  Harbour  there were s i g n i f i c a n t l y more male DF b i r d s (10) captured than female DF b i r d s (three) ( b i n o m i a l , p < . 0 5 ) . I o b t a i n e d r e p r o d u c t i v e i n f o r m a t i o n f o r both 1978 and f o r e i g h t males and s i x females (Table 2 - 1 1 ) . t i v e performance was predictable.  Two  1979  T h e i r reproduc-  s i m i l a r , but that o f females was  less  females a t Pender Harbour i n 1979 e x h i b i t e d  g r e a t e r n e s t t e n a c i t y and defence than males.  One  r a i s e d two young a f t e r l o s i n g her male p a r t n e r .  female  Another female  defended her nest a g a i n s t scavenging ravens f o r two days a f t e r her young were l o s t to raccoons.  68 DISCUSSION Colony  Formation  Most herons known to nest a t Pender Harbour foraged c l o s e to the colony s i t e .  The food demand o f young herons  ensures  t h a t f o r a g i n g parents r e t u r n r e g u l a r l y to t h e i r nests and, i f the maximum time away from the nest i s to be used f o r g a t h e r i n g food, f e e d i n g s i t e s must be c l o s e to the colony. Werschkul e t a l . (1977) found t h a t heron c o l o n i e s i n c o a s t a l Oregon are p l a c e d adjacent to good f e e d i n g grounds and colony s i z e was r e l a t e d to. the s i z e of. the a d j a c e n t estuaries.  C o l o n i e s are probably formed by groups o f herons  which congregate  a t the l a r g e e s t u a r i e s to f e e d .  Locally-  f e e d i n g herons formed the m a j o r i t y o f the Pender Harbour colony i n both  1978 and 1979 and probably determined i t s  location. Most herons n e s t i n g a t Pender Harbour i n 1978 s e l e c t e d a new mate and nest s i t e i n 1979. T h i s i s i n sharp c o n t r a s t to o t h e r c o l o n i a l s p e c i e s , e s p e c i a l l y g u l l s , which show cons i d e r a b l e colony, nest and mate f i d e l i t y between years (Southern and Southern  1982).  I t has been shown t h a t  k i t t i w a k e s ( R i s s a t r l d a c t y l a ) have improved r e p r o d u c t i v e success i f they mate with the same I n d i v i d u a l each year (Coulson and Thomas 1983).  F a c t o r s which can cause mate  s w i t c h i n g , such as death o f the former mate o r u n s u c c e s s f u l * r e p r o d u c t i o n , d i d not cause herons to switch a t Pender Harbour.  E i g h t o f 10 i n d i v i d u a l s p a i r e d i n 1978 were s t i l l  p r e s e n t i n the colony i n 1979 and a l l f i v e banded p a i r s were  69 s u c c e s s f u l i n 1978 yet none remained together i n 1979.  This  l a c k o f nest s i t e and mate f i d e l i t y c o i n c i d e s with r e s u l t s i n Chapter I which suggested  t h a t breeding herons f r e q u e n t l y move  between c o l o n i e s and e s t a b l i s h new  nests.  Changes i n l o c a -  t i o n s and numbers of nests d u r i n g the n e s t i n g season r e s u l t e d from u n s u c c e s s f u l b i r d s l e a v i n g and new  b i r d s e n t e r i n g the  Pender Harbour colony r a t h e r than from movements w i t h i n the colony.  Those f a c t s a g a i n suggest  t h a t herons show l i t t l e  attachment to s p e c i f i c n e s t i n g s i t e s .  Because o f t h i s l a c k  o f p r e d i c t a b i l i t y o f n e s t s o r mates, h e r o n r i e s are Important assembly areas f o r herons to f i n d new  mates and nest  sites  each year. Although  herons n e s t i n g i n p e r i p h e r a l n e s t s had  r e p r o d u c t i v e success  poorer  (Table 2-4), c e n t r a l n e s t s were not  p i e d by herons more dominant on the f e e d i n g a r e a s .  The  p o s i t i o n o f p a i r s i n a colony i s l a r g e l y dependent on  Meyerriecks n e s t s and  i960).  Others have observed  1978,  those f u r t h e s t from the ground are the f i r s t  (Parker I 9 8 O , Rodgers 1978, Henny and Bethers  are low  breeding  that older, e s t a b l i s h e d  by d i s p l a y i n g males, probably to a i d i n a t t r a c t i n g  h e i g h t may  a l s o be important  nest  the  males, which s e l e c t and defend nest s i t e s e a r l y i n the season p r i o r to the formation o f p a i r bonds (Rodgers  occu-  occupied  females  1971).  Nest  i n c o l o n i e s where average h e i g h t s  (<4.m) o r i n t r e e s p e c i e s such as cottonwood and  Douglas  f i r where there i s a l a r g e d i f f e r e n c e between the lowest  and  h i g h e s t n e s t s and there are many nests per t r e e .  nests  Higher  should be l e s s v u l n e r a b l e to t r e e - c l i m b i n g p r e d a t o r s s i n c e  70 lower nests would be encountered n e s t s may  first.  A l t e r n a t e l y , higher  be more v u l n e r a b l e to a v i a n p r e d a t o r s which come  from above.  At Pender Harbour there was  g e n e r a l l y one  per t r e e (Table 1-3). nest h e i g h t s v a r i e d l i t t l e SD = 1.51»  n = 65) and there was  (x = 26  m,  no r e l a t i o n s h i p between nest  occupancy o r r e p r o d u c t i v e success and nest h e i g h t . (I98O)  nest  Parker  noted t h a t r e t u r n i n g herons occupied nests i n a l l p a r t s  o f the c o l o n i e s and d i d not group t o g e t h e r .  Later a r r i v i n g  b i r d s were then able to occupy s i t e s between e s t a b l i s h e d p a i r s , who  had reduced  surrounding  the t e r r i t o r y defended to the area  t h e i r nests  a nest i n a heronry choose to n e s t . vacant n e s t s .  (Rodgers 1978).  The  immediately  f i n a l p o s i t i o n of  i s dependent on where subsequent b i r d s  At Pender Harbour there was  a l a r g e number o f  E a r l y a r r i v i n g b i r d s which chose nests near the  c e n t e r o f the a v a i l a b l e s i t e s may  s t i l l have ended up near the  edge o f the colony i f l a t e r a r r i v i n g b i r d s nested mostly one  side.  to any  T h i s suggests  individual.  that a l l s i t e s are e q u a l l y a v a i l a b l e  The p o s s i b l e advantages o f j o i n i n g a  colony, which are d e r i v e d mainly bors  (Wittenberger  to  from the p r o x i m i t y o f neigh-  I 9 8 I ) , would t h e r e f o r e be e q u a l l y a v a i l a b l e  to each o f i t s members.  Herons are a t t r a c t e d to colony  sites  to f i n d mates, to l o c a t e t h e i r n e s t s near good f e e d i n g s i t e s and to reduce the v u l n e r a b i l i t y o f t h e i r young to p r e d a t o r s by n e s t i n g i n groups.  71 P r e d a t i o n , Reproductive P r e d a t i o n was a t Pender Harbour.  Success and A d u l t S u r v i v a l  probably the primary cause o f nest  failure  P r e d a t i o n t y p i c a l l y r e s u l t s i n the l o s s  o f e n t i r e n e s t s (Jennl 1969. Dusi and Dusi 1968), i n comparison to s t a r v a t i o n o r s i b l i n g r i v a l r y , which reduce  the number  f l e d g e d per s u c c e s s f u l nest (McAloney 1973. P r a t t Owen i 9 6 0 ) .  1972,  Higher l o s s e s among p e r i p h e r a l nests (Table  a l s o i m p l i c a t e p r e d a t o r s as the cause. o f a colony are the f i r s t encountered they have fewer c l o s e neighbors tages o f swamping are reduced have been c o n s i d e r e d important  2-4)  Nests near the edge by p r e d a t o r s and, because  than c e n t r a l n e s t s , the advan-  (Wittenberger  1981).  Predators  causes o f nest f a i l u r e f o r  g r e a t blue herons i n o t h e r areas, and f o r c o l o n i a l s p e c i e s i n g e n e r a l ( H j e r t a a s 1982, Ward and Zahavi 1973.  Milstein  et a l . 1970). DF herons had more nest f a i l u r e s than r e s i d e n t s but, i n s u c c e s s f u l n e s t s , r a i s e d as many young as r e s i d e n t s (Table 2 - 2 ) . DF b i r d s must have chosen areas o u t s i d e Pender Harbour f o r feeding.  Two  o f those i n d i v i d u a l s were seen o n l y a t the b a i t  tanks while the o t h e r s were seen so i r r e g u l a r l y a t t i d a l  areas  t h a t I doubt i f they c o u l d have supported n e s t l i n g s without alternate feeding areas.  Thompson (1979b), i n Montana, and  P a r r l s and Grau ( 1 9 7 9 ) . on the Great Lakes,  showed t h a t some  g r e a t blue herons t r a v e l l e d up to 20 o r 30 km, to f e e d i n g areas from t h e i r n e s t i n g s i t e s .  respectively,  I f those d i s t a n c e s  a p p l y to herons a t Pender Harbour, some b r e e d i n g b i r d s may been f e e d i n g as f a r away as S e c h e l t .  have  Since s h o r t term movement  72 between Pender Harbour and S e c h e l t was seen, such l o n g d i s tance f o r a g i n g by breeding a d u l t s seems p o s s i b l e . Yom-Tov (1974) e x p e r i m e n t a l l y manipulated the food supply of b r e e d i n g crows and found that nest l o s s e s i n c r e a s e d when food was p l a c e d f u r t h e r from the n e s t .  He suggested that when  food i s d i s p e r s e d the n e s t l i n g s are more v u l n e r a b l e to predat i o n because nest.  the parents spend more time f a r away from the  DF herons may have more nest f a i l u r e s because  they  spend more time away from t h e i r n e s t s w h i l e f o r a g i n g f o r food. The reasons why DF herons f e d i n areas f a r away from  their  n e s t s , a p p a r e n t l y a t the r i s k o f l o s i n g t h e i r young, a r e not clear.  Although LF herons were not c l e a r l y dominant over  n e s t i n g DF b i r d s , i t i s p o s s i b l e t h a t DF herons were f o r c e d away from Pender Harbour by c o m p e t i t i o n from LF b i r d s .  Several  LF herons excluded a l l o t h e r herons from s e l e c t e d p a r t s o f the b a i t tanks.  D i f f e r e n c e s i n number o f i n t e r a c t i o n s between LF  and DF herons probably r e l a t e to t h e i r d i f f e r e n t occurrence on f e e d i n g areas (Table 2 - 1 ) .  Fewer i n t e r a c t i o n s f o r DF herons  was p r o b a b l y a r e s u l t r a t h e r than a cause o f t h e i r observed lower use o f f e e d i n g s i t e s w i t h i n Pender Bayer  Harbour.  (I978) found that some herons which m a i n t a i n  f e e d i n g t e r r i t o r i e s over w i n t e r had b e t t e r s u r v i v a l than nont e r r i t o r i a l herons.  DF herons n e s t i n g a t Pender Harbour  may  have t r a v e l l e d to d i s t a n t f e e d i n g areas to m a i n t a i n p r e f e r r e d territories.  Improved w i n t e r s u r v i v a l may have been more  important to the i n d i v i d u a l s than decreased r e p r o d u c t i v e success.  My data was i n s u f f i c i e n t to t e s t i f DF b i r d s had  73 above average over-winter s u r v i v a l and I d i d not d i s t i n g u i s h between t e r r i t o r i a l and n o n - t e r r i t o r i a l herons w i t h i n Pender Harbour d u r i n g the w i n t e r . C o l o n i a l N e s t i n g and Information Exchange Krebs (197*0  p o s t u l a t e d t h a t t r a n s f e r o f f e e d i n g informa-  t i o n may be one o f the p r i n c i p a l advantages to c o l o n i a l n e s t i n g i n herons.  There was no evidence to suggest  t h a t herons a t  Pender Harbour used any type o f f e e d i n g a r e a i n f o r m a t i o n exchange.  N e i t h e r p a i r e d herons nor neighbors tended  i n the same areas as would be expected o t h e r to good f e e d i n g s i t e s tended  i f herons f o l l o w e d each  (Krebs 1974).  to feed i n d i f f e r e n t areas  to feed  In f a c t , p a i r s  (Table 2 - 6 ) .  Prey abundance and d i s t r i b u t i o n was p r e d i c t a b l e and f e e d i n g r a t e s o f herons d i d not v a r y g r e a t l y on l o c a l areas  (Table 2 - 7 ) .  tidal  Large t i d e s , i n June, expose the maximum  e s t u a r l n e h a b i t a t c o i n c i d e n t with the peak prey abundance, peak a d u l t f e e d i n g r a t e s ( P i g . 2-3) and maximum food demand o f the young herons.  Reproductive  synchrony  the Pender Harbour colony probably ensures  and t i m i n g a t  t h a t the food demand  c o i n c i d e s with the seasonal changes i n supply.  A single adult  s u c c e s s f u l l y r a i s i n g two young suggests t h a t food i s not l i m i t ing.  I found no evidence o f the reduced brood s i z e s  normally  a s s o c i a t e d with food l i m i t a t i o n and s t a r v a t i o n (Des Granges 1979. P r a t t 1972, Owen i 9 6 0 ) , nor was there any r e l a t i o n between f e e d i n g r a t e s o f parents and number o f young f l e d g e d . those f a v o r a b l e circumstances  Under  there i s no need f o r herons to  "share" f e e d i n g area i n f o r m a t i o n .  74 Although  much o f my Information i n d i c a t e s t h a t many  herons a t Pender Harbour had s p e c i f i c f e e d i n g areas  (Table 2 - 6 ) ,  o t h e r data a l s o shows t h e i r a b i l i t y to e x p l o i t e x t r a o r d i n a r y o r u n u s u a l l y abundant food s u p p l i e s .  S i g h t i n g s o f f o u r o f the  13 DF non-colony b i r d s (Table 2-1) suggest  t h a t they came from  f r e q u e n t l y used areas o u t s i d e Pender Harbour.  B i r d A43 was  r e s i g h t e d o n l y a t S e c h e l t , s u g g e s t i n g t h a t i t may have been a DF heron from the S e c h e l t colony when i t was captured i n 1978. The movements o f A82 and A84, and the s i g h t i n g data f o r A48, show t h a t they frequented o t h e r areas and o n l y o c c a s i o n a l l y v i s i t e d Pender Harbour.  Those b i r d s were p r o b a b l y  attracted  to Pender Harbour by the abundant food supply a t the b a i t  tanks.  Some o f the b r e e d i n g DF herons a t Pender Harbour may have had s i m i l a r movement h a b i t s .  I f those b i r d s o c c a s i o n a l l y l o c a t e d  e x t r a o r d i n a r y f e e d i n g s i t e s , t h a t i n f o r m a t i o n c o u l d be t r a n s f e r r e d to o t h e r n e i g h b o r i n g a d u l t s i n the colony when they r e t u r n e d to feed t h e i r young. L o c a l food shortages have o c c u r r e d a t h e r o n r i e s i n o t h e r areas  (review by Des Granges 1979) p o s s i b l y due to u n p r e d i c t -  a b l e d e c l i n e s i n prey abundance o r poor weather c o n d i t i o n s . I f the l o c a l food supply a t the Pender Harbour colony were t o fall,  DF herons i n the colony c o u l d l e a d o t h e r colony members  to a l t e r n a t e f e e d i n g a r e a s . r e q u i r e d to adequately  A l o c a l food shortage would be  t e s t the i n f o r m a t i o n exchange  u s i n g g r e a t blue herons a t Pender Harbour.  hypothesis  75 Sex and Reproductive  Success  Great blue heron p a i r s share the r e s p o n s i b i l i t y o f i n c u b a t i n g and f e e d i n g the young.  A d u l t herons tend the n e s t  c o n t i n u o u s l y d u r i n g i n c u b a t i o n and f o r the f i r s t three to f o u r weeks a f t e r h a t c h i n g ( P r a t t 1970).  From June 1 u n t i l  fledging  both parents r e t u r n r e g u l a r l y to feed the young, but do not m a i n t a i n constant v i g i l a n c e a t t h e i r n e s t s . I have some i n f o r m a t i o n which suggests t h a t d i f f e r i n g h a b i t s o f males and females may  affect reproduction.  Sig-  n i f i c a n t l y more males than females were captured i n the non-colony  group a t Pender Harbour.  Although  DF  there i s no  i n f o r m a t i o n on the sex r a t i o i n the g r e a t blue heron p o p u l a t i o n , there are g e n e r a l l y more females than males i n p o p u l a t i o n s o f l a r g e c o l o n i a l s p e c i e s (Coulson and Thomas 1983).  Band  r e c o v e r i e s a t Pender Harbour suggest t h a t a d u l t m o r t a l i t i e s were d i v i d e d e q u a l l y between females I f we  (seven) and males  (six).  c o n s e r v a t i v e l y assume an equal male/female r a t i o i n  surrounding areas, more DF males must have t r a v e l l e d to the b a i t tanks i n Pender Harbour to i n c r e a s e t h e i r capture quency.  fre-  I t i s p o s s i b l e t h a t male DF herons feed a t g r e a t e r  d i s t a n c e s from t h e i r nests than females and a r e , t h e r e f o r e , l e s s a t t e n t i v e a t the nest  site.  I f i n d i v i d u a l herons m a i n t a i n s i m i l a r r e p r o d u c t i v e e f f o r t from year to year, changes i n r e p r o d u c t i v e success  probably  r e l a t e to o t h e r f a c t o r s such as the e f f o r t o f the mate. o f s i x females  Three  s u c c e s s f u l i n 1978, f a i l e d i n 1979 when p a i r e d  with d i f f e r e n t males.  Only one o f seven males i n v o l v e d i n  76 i  s u c c e s s f u l 1978 matings f a i l e d i n 1979  (Table 2-11).  those o b s e r v a t i o n s are not s i g n i f i c a n t l y d i f f e r e n t , suggest  Although they  t h a t female r e p r o d u c t i v e success can be a f f e c t e d  the behavior o f t h e i r male p a r t n e r s .  by  Other o b s e r v a t i o n s o f  female t e n a c i t y a t the nest and a b i l i t y to r a i s e young alone suggest  t h a t females m a i n t a i n a h i g h e r and more c o n s i s t e n t  l e v e l o f r e p r o d u c t i v e e f f o r t than males.  The  suggested  d i f f e r e n c e s i n the movements and nest t e n a c i t y o f males and females may  I n d i c a t e t h a t males have g r e a t e r r e s p o n s i b i l i t y  f o r f i n d i n g food, while females have g r e a t e r r e s p o n s i b i l i t y f o r tending the young.  CONCLUSIONS The Pender Harbour heron colony was  composed o f a core  group o f LF herons which f e d p r i n c i p a l l y i n the two  adjacent  t i d a l e s t u a r i e s d u r i n g the day and a t l i v e b a i t f i s h ponds at night. (DF)  c o n s t i t u t e d about 22 percent o f the Pender Harbour  colony. 1978  Herons with f e e d i n g areas o u t s i d e Pender. Harbour  Most herons s e l e c t e d a new  to 1979.  i n Chapter  The  mate and nest s i t e  colony s h i f t s and s i z e f l u c t u a t i o n s  from noted  I undoubtedly r e l a t e to the l a c k o f attachment o f  b r e e d i n g herons to n e s t i n g s i t e s o r mates.  C e n t r a l nest  sites  were most s u c c e s s f u l but d i f f e r e n c e s i n i n d i v i d u a l dominance, determined occupancy.  a t f e e d i n g s i t e s , were not r e l a t e d to nest  site  Herons are probably a t t r a c t e d to c o l o n i e s p r i m a r i l y  to f i n d s u i t a b l e mates, to l o c a t e t h e i r n e s t s near good f e e d i n g  77 s i t e s and to reduce the v u l n e r a b i l i t y o f t h e i r young to  preda-  t o r s by swamping. DF herons s u f f e r e d more nest f a i l u r e s than LF b i r d s , f l e d g e d as many young as LF herons i n s u c c e s s f u l n e s t s .  but The  frequent l o s s o f e n t i r e c l u t c h e s , h i g h e r l o s s e s i n p e r i p h e r a l n e s t s and d i r e c t o b s e r v a t i o n s o f p r e d a t o r s i n the confirmed p r e d a t i o n as the primary  colony  cause o f nest l o s s e s .  DF herons probably spent more time away from t h e i r nests while f o r a g i n g f o r food, and thereby exposed t h e i r young to h e a v i e r predation. DF herons n e s t i n g a t Pender Harbour may  have been l e s s  dominant a t f e e d i n g s i t e s than LF b i r d s , so i t i s p o s s i b l e t h a t they were f o r c e d to use more d i s t a n t f e e d i n g s i t e s i n t r a s p e c i f i c competition.  by  Other r e s e a r c h i n d i c a t e s t h a t  herons which m a i n t a i n f e e d i n g t e r r i t o r i e s have b e t t e r overwinter s u r v i v a l .  DF herons n e s t i n g a t Pender Harbour may  continued to use d i s t a n t f e e d i n g areas to m a i n t a i n  have  territories  which were v a l u a b l e f o r w i n t e r s u r v i v a l even though t h e i r r e p r o d u c t i v e success was  lowered.  Exchange o f i n f o r m a t i o n about f e e d i n g areas d i d not appear to be o c c u r r i n g i n the Pender Harbour colony. and d i s t r i b u t i o n was  p r e d i c t a b l e i n time and  r e s u l t s o f s e i n e sampling Peak prey abundance and  Prey abundance space, based on .  and o b s e r v a t i o n s o f f e e d i n g  herons.  feeding h a b i t a t a v a i l a b i l i t y occurred  c o i n c i d e n t with peak food demands o f young herons i n the colony. f o r any  Under those circumstances  there was  o b v i o u s l y no need  Information exchange to l o c a t e good f e e d i n g a r e a s .  78  L o c a l food shortages and s t a r v a t i o n have been observed i n other heronries.  Under those c o n d i t i o n s , LF herons c o u l d  f o l l o w DF b i r d s to a l t e r n a t e f e e d i n g a r e a s .  Food  shortages  and u n p r e d i c t a b l e supply should be demonstrated b e f o r e the i n f o r m a t i o n exchange h y p o t h e s i s f o r c o l o n i a l n e s t i n g can be t e s t e d using great blue I n d i r e c t evidence r a n g i n g than females. at  herons. suggests  t h a t males may be wider  Because males may spend l e s s  time  the nest and l e a v e the nest unattended, r e p r o d u c t i o n f o r  some females may be l i m i t e d by t h i s b e h a v i o r o f the male. Since males i n i t i a t e n e s t i n g and colony formation,  their  movements may a l s o be r e s p o n s i b l e f o r some o f the observed colony  instability.  79 GENERAL DISCUSSION AND  RECOMMENDATIONS  Heronries f r e q u e n t l y change l o c a t i o n s o r f l u c t u a t e i n size dramatically.  Such movements and changes i n s i z e have  p r e v i o u s l y been a s s o c i a t e d with d i s t u r b i n g i n f l u e n c e s o r p r e d a t i o n and were c o n s i d e r e d u n n a t u r a l o r d e t r i m e n t a l o c c u r r e n c e s . Great blue herons d i f f e r from o t h e r c o l o n i a l s p e c i e s because c o l o n i e s are not composed o f d i s c r e t e groups o f b i r d s which r e t u r n a n n u a l l y to the same s i t e . o f herons gather and  Each year v a r y i n g numbers  form c o l o n i e s near good f e e d i n g s i t e s but  not n e c e s s a r i l y a t p r e v i o u s l y used l o c a t i o n s . and nest s i t e f i d e l i t y , observed  a t one  The l a c k o f mate  d i s t u r b e d colony,  may  be i n d i c a t i v e o f herons g e n e r a l l y and probably c o n t r i b u t e s to the observed  i n s t a b i l i t y o f many h e r o n r i e s .  r e l o c a t e d bred s u c c e s s f u l l y a t new  C o l o n i e s which  l o c a t i o n s and may,  t e m p o r a r i l y , have avoided some o f the p r e d a t o r s which established heronries. was  at least frequented  The g r e a t e s t d i s t a n c e moved by a  heronry  10 k i l o m e t e r s , but most moves were under f i v e k i l o m e t e r s  i n t h i s study.  A c t i v i t i e s which may  cause r e l o c a t i o n s should  be avoided u n l e s s there i s s u i t a b l e s i m i l a r h a b i t a t a v a i l a b l e w i t h i n 10 k i l o m e t e r s .  The p r o x i m i t y o f p r e f e r r e d f e e d i n g areas  to p o t e n t i a l n e s t i n g areas may  be important  i n determining  the  maximum d i s t a n c e a heronry might move. Human d i s t u r b a n c e s had  the e f f e c t o f i n c r e a s i n g the  o f n a t u r a l p r e d a t o r s i n h e r o n r i e s and colony r e l o c a t i o n s .  Although  success  frequently resulted i n  some h e r o n r i e s adapted to human  a c t i v i t i e s , o t h e r s , away from r e g u l a r human a c t i v i t y where  80 a d u l t s f l e d from people, n e s t i n g season  should be u n d i s t u r b e d d u r i n g  the  (April-July).  The percentage o f nests s u c c e s s f u l was to assess r e p r o d u c t i o n i n h e r o n r i e s .  the best  The method o f  statistic determin-  i n g the numbers o f s u c c e s s f u l and u n s u c c e s s f u l p a i r s ,  without  c a u s i n g a major d i s t u r b a n c e i n the c o l o n i e s , should be f u r t h e r explored.  Colony censuses should i n c l u d e an a c c u r a t e count o f  occupied and vacant n e s t p l a t f o r m s d u r i n g f l e d g l i n g  counts.  In c o l o n i e s adapted to human a c t i v i t i e s the r e l a t i o n s h i p between n e s t occupancy and numbers o f breeding p a i r s c o u l d be f u r t h e r examined. Banding o f i n d i v i d u a l s , a t one  colony, has  shown that  breeding herons have d i f f e r i n g h a b i t s which r e l a t e to r e p r o d u c t i o n , over-winter  s u r v i v a l and  food-finding.  Males  may  have g r e a t e r r e s p o n s i b i l i t y f o r f o r a g i n g and f o o d - f i n d i n g w h i l e females may  p r o v i d e more n e s t defence.  f e e d i n g herons had lower r e p r o d u c t i v e success f e e d e r s , they may  have gained long-term  t a i n i n g t e r r i t o r i e s important  choosing  than  local  advantages by main-  f o r over-winter  which t r a v e l f u r t h e r to feed may  Although d i s t a n t  survival.  Birds  a l s o have more o p t i o n s i n  c o l o n i e s i n which to n e s t .  Further studies using  banded herons could b e t t e r d e f i n e the r o l e s o f males and females and  the importance o f d i s t a n t feeders to  o f c o l o n i e s and l o c a t i o n o f f e e d i n g a r e a s .  formation  81 LITERATURE CITED BAYER, R.D. 1978. Aspects o f an Oregon E s t u a r l n e Great Blue Heron P o p u l a t i o n . I n : Wading B i r d s . Research Report No. 7, N a t i o n a l Audubon S o c i e t y , New York. A. Sprunt, J.C. Ogden and S. W i n c k l e r , eds. Pp. 213-217. BAYER, R.D. 1979. B a l d Eagle-Great Blue Heron I n t e r a c t i o n s . M u r r e l e t 60: 32-33. BAYER, R.D. I98I. A r r i v a l and Departure Frequencies o f Great Blue Herons a t Two Oregon E s t u a r l n e C o l o n i e s . The Auk 98: 589-595. BENNING, W.F. 1969. A Survey o f Great Blue H e r o n r i e s 1964-69. K i n g b i r d 19: 85-90. BLUS, L . J . , C.J. HENNY and T.E. KAISER. 1980. P o l l u t i o n Ecology o f Breeding Great Blue Herons i n the Columbia B a s i n , Oregon and Washington. M u r r e l e t 61: 63-71. CAMPBELL, R.W., M.G. SHEPHARD and W.C. WEBER. 1973. Vancouver b i r d s i n 1971. Vancouver Nat. H i s . Soc. 88 pp. CAMPBELL, R.W., 1974. Soc.  M.G. SHEPHARD, B.A. MacDONALD, and W.C. WEBER. Vancouver b i r d s i n 1972. Vancouver Nat. H i s t . 96 pp.  CANADIAN WILDLIFE SERVICE. 1971. P e s t i c i d e s and w i l d l i f e . C.W.S. Rept., I n f o r m a t i o n Canada, Ottawa. 24 pp. COOK, D.C.  1978. Grey herons h o l d i n g f e e d i n g t e r r i t o r i e s on the Ythan E s t u a r y . B i r d Study 25 : 11-16.  C0ULS0N, J.C. and C.S. THOMAS. I983. Mate c h o i c e i n the Kittlwake g u l l . I n : Mate C h o i c e . P.P.G. Bateson, ed. Cambridge Univ. P r e s s . CUSTER, T.W. and R.G. 0SB0RN. 1978. Feeding H a b i t a t Use by C o l o n i a l l y - B r e e d i n g Herons, E g r e t s and I b i s e s i n North C a r o l i n a . The Auk 95' 733-743. DES GRANGES, J . L . 1978. Adaptive Value o f S o c i a l Behaviour i n the Great Blue Heron (Ardea h e r o d l a s ) . I n : P r o c . 1978 Conf. o f the C o l o n i a l W a t e r b i r d Group: 192-201. DES GRANGES, J . L . 1979. Abandoned Windmill Used as a N e s t i n g S i t e by Great Blue Herons. Canadian F i e l d - N a t u r a l i s t 93 : 439-440.  82 DES  GRANGES, J . L . I 9 8 O . A Canadian program f o r s u r v e i l l a n c e o f Great Blue Heron (Ardea h e r o d i a s ) p o p u l a t i o n s . P r o c . C o l o n i a l W a t e r b i r d Group 1979: 59-69.  DES  GRANGES, J.L. and P. LAPORTE. I 9 8 I . T h i r d Tour o f I n s p e c t i o n o f Quebec H e r o n r i e s 1979. C.W.S. P r o g r e s s Note No. 1 2 3 . 10 pp.  DES  GRANGES, J.L. and P. LAPORTE. I 9 8 3 . Fourth and F i f t h Tours o f I n s p e c t i o n o f Quebec H e r o n r i e s , I 9 8 O - 8 I . C.W.S. P r o g r e s s Note No. 1 3 9 . 11 PP.  DUSI, J . L . and R.T. DUSI. I 9 6 8 . E c o l o g i c a l f a c t o r s cont r i b u t i n g to n e s t i n g f a i l u r e i n a heron c o l o n y . Wilson B u l l . 80: 458-466. FORBES, L.S. I98O. B e h a v i o u r a l s t u d i e s o f Great Blue Herons (Ardea h e r o d i a s ) a t Pender Harbour and S e c h e l t , B.C., i n 1980. C.W.S. Manuscript Rept., D e l t a , B. C. 60 pp. FORBES, L.S., K. SIMPSON, J.P. KELSALL and D.R. FLOOK. I 9 8 3 . Great b l u e heron c o l o n i e s i n B r i t i s h Columbia. C. W.S. Rept., D e l t a , B.C. 66 pp. FRY,  K.  I 9 8 O . Memo r e g a r d i n g eagle a t t a c k s a t the Crescent c o l o n y . C.W.S. F i l e 9050-Herons, D e l t a , B.C., June 9, 1980.  HEDEEN, S. I967. Feeding Behaviour o f the Great Blue Heron i n I t a s c a S t a t e Park, Minnesota. Loon 39: 116-120. HENNY, C.J. and M.R. BETHERS. 1 9 7 1 . P o p u l a t i o n Ecology o f the Great Blue Heron with S p e c i a l Reference t o Western Oregon. Canadian F i e l d - N a t u r a l i s t 8 5 : 205-209.  HENNY, C.J. 1 9 7 2 . An a n a l y s i s o f the p o p u l a t i o n dynamics o f s e l e c t e d a v i a n s p e c i e s with s p e c i a l r e f e r e n c e to changes d u r i n g the modern p e s t i c i d e e r a . U.S. F.&W. S e r v i c e W i l d l i f e Res. Rept. No. 1, Washington, D.C. HJERTAAS, D.G. 1 9 8 2 . Great Blue Herons and Racoons a t Nlcolle Flats. Blue Jay 40: 36-41. JENNI, D.A. I 9 6 9 . A Study o f the Ecology o f Four S p e c i e s o f Herons d u r i n g the Breeding Season a t A l i c e Lake, Alachua County, F l o r i d a . E c o l . Monogr. 39: 245-270 JEREMA, R.S. 1 9 7 3 . B i r d s o f P o r t Coquitlam. Manuscript Report, P o r t Coquitlam M u n i c i p a l i t y . 59 PP«  83 KELSALL, J.P. and K. SIMPSON. I98O. A three year study o f the g r e a t b l u e heron In South Western B r i t i s h Columbia. P r o c . 1979 Conf. o f the C o l o n i a l W a t e r b i r d Group: 69-74. KOONZ, W.H. I98O. B a l d eagle nest i n a Manitoba c o l o n y . Blue J a y 38: 4-9.  heron  KREBS, J.R. 1974. C o l o n i a l n e s t i n g and s o c i a l f e e d i n g as s t r a t e g i e s f o r e x p l o i t i n g food r e s o u r c e s i n the Great Blue Heron (Ardea h e r o d l a s ) . Behaviour 51: 99-134. MARK, D.M. 1974. P r e l i m i n a r y R e s u l t s o f Some Great Blue Heron (Ardea h e r o d l a s ) S t u d i e s i n the Vancouver C h e c k l i s t Area. Vancouver Nat. H i s t . Soc. D i s c o v e r y 3- 38-44. MARK, D.M. 1976. An Inventory o f Great Blue Heron (Ardea h e r o d l a s ) N e s t i n g C o l o n i e s i n B r i t i s h Columbia. Northwest Science 50: 32-40. McALONEY, K. 1973. The Breeding B i o l o g y o f Great Blue Herons on Tobacco I s l a n d , Nova S c o t i a . Canadian F i e l d - N a t u r a l i s t 87: 137-140. MEYERRIECKS, A . J . i 9 6 0 . Comparative breeding behavior o f f o u r s p e c i e s o f North American herons. Publ. N u t t a l l O r n i t h o l . Club No. 2: 1-158. MILSTEIN, P. l e S., I . PRESTT and A.A. BELL. 1970. The Breeding C y c l e o f the Grey Heron. Ardea 58: 171-257. MOCK, D.W.  1976. P a i r Formation D i s p l a y s o f the Breat Blue Heron. Wilson B u l l . 88: 185-230.  OWEN, D.F. i 9 6 0 . The n e s t i n g success o f the heron (Ardea c i n e r e a ) i n r e l a t i o n t o the a v a i l a b i l i t y o f food. P r o c . Z o o l . Soc. London 133: 597-617. PAINE, J.M. 1972. A Study o f C o l o n i a l N e s t i n g i n the Great Blue Heron (Ardea h e r o d l a s ) . Unpub. B. Sc. t h e s i s . Dept. o f Zoology, U.B.C. 61 pp. PARKER, J . 1980. Great Blue Herons (Ardea h e r o d l a s ) i n Northwestern Montana: N e s t i n g H a b i t a t Use and the E f f e c t s o f Human D i s t u r b a n c e . M. Sc. t h e s i s , U. o f Montana. 82 pp. PARRIS, R.W. and G.A. GRAU. 1979. Feeding S i t e s o f Great Blue Herons i n Southwestern Lake E r i e . P r o c . 1978 Conf. o f the C o l o n i a l Waterbird Group: 110-113.  84 PIEFER, R.W. 1 9 7 9 . Great Blue Herons Foraging f o r Small Mammals. W i l s o n B u l l . 9 1 : 6 3 O - 6 3 I . PRATT, H.M. 1 9 7 0 . Breeding B i o l o g y o f Great Blue Herons and Common E g r e t s i n C e n t r a l C a l i f o r n i a . Condor 72:  407-416.  PRATT, H.M. 1 9 7 2 . N e s t i n g Success o f Common E g r e t s and Great Blue Herons i n the San F r a n c i s c o Bay Region. Condor 74: 4 4 7 - 4 5 3 . 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Great Blue Herons and D o u b l e - c r e s t e d Cormorant C o l o n i e s i n the P r a i r i e P r o v i n c e s . Canadian F i e l d - N a t u r a l i s t 8 7 : 4 2 7 - 4 3 2 . WARD, P. and A. ZAHAVI. 1 9 7 3 . The importance o f c e r t a i n assemblages o f b i r d s as " i n f o r m a t i o n c e n t e r s " f o r food-finding. I b i s 115: 5 1 7 - 5 3 4 . WERSCHKUL, D.F., E. McMAHON and M. LEITSCHUH. 1 9 7 6 . Some e f f e c t s o f human a c t i v i t i e s on the Great Blue Heron i n Oregon. W i l s o n B u l l . 8 8 : 6 6 1 - 6 6 2 . WERSCHKUL, D., E . McMAHON, M. LEITSCHUH, S. ENGLISH, C. SIBINSKI and G. WILLIAMSON. 1 9 7 7 . O b s e r v a t i o n s on the r e p r o d u c t i v e ecology o f the Great Blue Heron (Ardea h e r o d i a s ) i n Western Oregon. M u r r e l e t 5 8 : 7 - 1 2 . WERSCHKUL, D.F. 1 9 7 9 . N e s t i n g m o r t a l i t y and the a d a p t i v e s i g n i f i c a n c e o f e a r l y locomotion i n the l i t t l e blue heron. Auk 9 6 : 1 1 6 - 1 3 0 . WITTENBERGER, J . F . I 9 8 I . Animal S o c i a l Behaviour. P r e s s , Boston. 705 PP.  Duxbury  YOM-TOV, Y. 1 9 7 4 . The e f f e c t o f food and p r e d a t i o n on breedi n g d e n s i t y and success, c l u t c h s i z e and l a y i n g date o f the crow (Corvus c o r o n e ) . J . Anim. Ecology 4 3 : 2J-79-/+98.  86 APPENDIX D i s c r i m i n a n t f u n c t i o n used to determine the sex o f banded herons a t Pender Harbour M o r p h o l o g i c a l measurements ( b i l l , head plume, t a r s u s , tail  and wing l e n g t h and weight) were o b t a i n e d from 19 dead  and 79 l i v i n g g r e a t b l u e herons. the  25  n e a r e s t mm  B i l l : measured from the t i p o f the b i l l  to the p o i n t  which the s k i n o f the forehead j o i n s the b i l l . 2.  to  u s i n g a s t e e l tape, and weight to the n e a r e s t  g. 1.  at  Measurements were taken to  Head plume:measured from the attachment on the s k u l l  the end o f the l o n g e s t plume. 3.  Tarsus:  w i t h the l e f t l e g extended to approximately  130° a t the knee j o i n t , measured from the j o i n t  indentation  on the a n k l e to the j o i n t i n d e n t a t i o n on the knee. 4. to  Tail:  measured from the base o f the p i n e a l g l a n d  the end o f the l o n g e s t t a i l 5.  Wing:  feather.  w i t h the b i r d r e s t r a i n e d and l a i d on i t s r i g h t  s i d e , measured from the l e a d i n g edge (elbow) o f the l e f t to  the end o f the l o n g e s t f l i g h t 6.  of  Weight:  the d i a l  wing  feather.  r e s t r a i n e d b i r d s were l a i d i n the c r a d l e  scale.  Dead specimens were c o l l e c t e d mainly d u r i n g the w i n t e r in  south c o a s t a l B.C.  Sex was determined d u r i n g autopsy by  Dr. A.C. M a c N e i l l , A g r i c u l t u r e Canada, H e a l t h o f Animals Branch.  Laparotomies were done to determine sex o f three  a d u l t l i v i n g b i r d s captured a t Pender Harbour i n 1978.  87 I n c i s i o n s were made i n the l e f t abdominal w a l l using l o c a l a n e s t h e t i c and  xylocaine  gonads observed u s i n g a h i g h i n t e n s i t y  microscope l i g h t . Using measurements from dead o r laparotomized males ( e i g h t ) and  females (13) a l i n e a r d i s c r i m i n a n t  developed a f t e r the method o f Rao  (1973).  The  function  was  function  was  used to determine the sex o f J2 banded herons, which were members o f the i n 1978  18 banded p a i r s i n the Pender Harbour  o r 1979.  colony  Assigned sexes f o r each p a i r e d b i r d were  examined to ensure that each p a i r c o n s i s t e d o f a male and female. lation  A d d i t i o n a l information was  such as o b s e r v a t i o n s  used i n c o r r e c t i n g the sexual  three i n d i v i d u a l s .  Following  o f the e n t i r e group o f now  a  o f copu-  c l a s s i f i c a t i o n of  t h i s v e r i f i c a t i o n , measurements  c l a s s i f i e d b i r d s were used to  develop a second d i s c r i m i n a n t f u n c t i o n which was  a p p l i e d to  the remaining banded b i r d s . The measurements I used i n determining the sex o f banded b i r d s are shown i n Table 1. tinued during  Two  measurements were d i s c o n -  the course o f the t r a p p i n g due  to  difficulties  i n o b t a i n i n g c o n s i s t e n t measurements ( t a i l length) o r obvious large v a r i a t i o n s unrelated  to age  o r sex  (head plume).  o f three l a p a r o t o m i e s attempted on a d u l t b i r d s were ful.  D i f f i c u l t i e s i n r e s t r a i n i n g l a r g e herons, poor  l a b o r a t o r y c o n d i t i o n s and f u r t h e r attempts.  Two  observed s i n c e and one  extended h a n d l i n g  time  o f the three b i r d s Involved  Two  successfield  precluded have been  s u c c e s s f u l l y r a i s e d f o u r young i n  Laparotomy i s a v i a b l e , although probably unnecessary.  1979.  88 technique i n determining the sex o f l i v i n g herons, g i v e n proper equipment and working  conditions.  Table 2 shows the  c o e f f i c i e n t s o f the l i n e a r d i s c r i m i n a n t f u n c t i o n  developed  u s i n g measurements o f dead (known sex) and p a i r e d l i v i n g herons.  Both f u n c t i o n s a r e e v a l u a t e d f o r each  and the one with the lower v a l u e determines Of 53 i n d i v i d u a l s o f known sex (dead o were c o r r e c t l y c l a s s i f i e d .  individual  the sex (Rao 1973)  p a i r e d b i r d s ) 52 (9&%)  Table 3 shows the m o r p h o l o g i c a l  measurements o f c l a s s i f i e d herons.  Using p o s t e r i o r proba-  b i l i t i e s over 70% o f the b i r d s c o u l d be c l a s s i f i e d with 95% confidence.  I used t h i s technique to a s s i g n sexes to a l l the  banded herons a t Pender Harbour.  LITERATURE CITED RAO, C.R.  1973. L i n e a r S t a t i s t i c a l Inference and I t s Applications. Second E d i t i o n , Wiley, New York:  574-581.  0  89 T a b l e 1.  M o r p h o l o g i c a l measurements o f 79 g r e a t blue herons captured a t Pender Harbour i n 1978 and 1979. N  Min.  Max.  Mean  SD  (mm)  79  116  146  132  8.34  Tarsus l e n g t h (mm)  79  133  180  160  11.02  Wing l e n g t h  (mm)  79  462  544  500  18.01  Tail  (mm)  68  170  230  195  12.56  (kg)  79  1.87  2.97  2.34  .25  Bill  length  length  Weight  Table 2.  C o e f f i c i e n t s o f the l i n e a r d i s c r i m i n a n t f u n c t i o n based on measurements o f known sex and p a i r e d g r e a t blue herons i n B r i t i s h Columbia, 1979.  Variable  Constant  Male  Female  -855.71  -745.97  3.07  2.64  B i l l length Tarsus l e n g t h Wing l e n g t h N  -  0.43 2.65  24  -  0.49 2.56  29  90 Table 3 .  M o r p h o l o g i c a l measurements o f known male and female g r e a t blue herons i n south c o a s t a l B r i t i s h Columbia. Sex  Min.  Max.  Mean  SD  N  Bill length  (mm)  •M F  129 112  146 131  137.0 123.9  4.43 4.72  24 29  Tarsus length  (mm)  M F  155 135  177 165  165.9 152.0  6.72 7.04  24 29  Wing length  (mm)  M F  470 465  544 500  505.7 483.0  13.75 8.69  24 29  Weight  (kg)  M F  1.53 1.90  3.07 3.27  2.48 2.11  0.29 0.34  24 29  PUBLICATIONS  SIMPSON, KEITH and Banding Harbour, Colonial  J.P. KELSALL. 1978. C a p t u r e and of A d u l t Great Blue Herons at Pender B r i t i s h Columbia. P r o c e e d i n g s of the W a t e r b i r d G r o u p , 1978 : 71 - 78.  and J . P . K E L S A L L . 1978. Preliminary Studies of G r e a t B l u e H e r o n C o l o n i e s , 1977. Canadian Wildlife Service. Manuscript Report. 20 p. and J . P . K E L S A L L . 1978. The W i l m e r N a t i o n a l W i l d l i f e A r e a ; W i l d l i f e and H a b i t a t s . Canadian W i l d l i f e Serv. Manuscript Report. 39 p.  K E L S A L L , J . P r and K. SIMPSON. 1979. A Three Year Study of t h e G r e a t B l u e H e r o n i n S o u t h w e s t e r n B r i t i s h Columbia. P r o c . C o l o n i a l W a t e r b i r d G r o u p , 1979. Vol. 3 : 69-74.  1980. Indirect K E L S A L L , J . P . , E.S. TELFER and K.- SIMPSON. D e t e r m i n a t i o n of U n g u l a t e Foot A r e a . Canadian J o u r n a l of Zoology. 58(3) : 464 - 466.  

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