@prefix vivo: . @prefix edm: . @prefix ns0: . @prefix dcterms: . @prefix skos: . vivo:departmentOrSchool "Science, Faculty of"@en, "Zoology, Department of"@en ; edm:dataProvider "DSpace"@en ; ns0:degreeCampus "UBCV"@en ; dcterms:creator "Runyan, Craig Steven"@en ; dcterms:issued "2010-03-03T22:09:11Z"@en, "1979"@en ; vivo:relatedDegree "Master of Science - MSc"@en ; ns0:degreeGrantor "University of British Columbia"@en ; dcterms:description """The objectives of the study were to determine the year-round distribution and habitat selection of four marsh passerine species, as described by vegetation type and its physical characteristics, and to investigate interspecific competition as a factor in the habitat selection of the Long-billed Marsh Wren and the Red-winged Blackbird. Fulfillment of these objectives should help the B.C. Fish and Wildlife Branch to assess the effects of their management plans on marsh passerines. I determined the abundance of four passerine species in different vegetation types via marsh census transects over the period of one year. Nesting habitat and breeding information on marsh wrens and redwings was obtained via nest study plots. The results were: Areas traversed from the central and deepest marsh outward towards higher ground are inhabited by redwings, marsh wrens. Common Yellowthroats, and Song Sparrows, respectively. Habitats of wrens and redwings are spatially and temporally segregated. Wrens use the "Dense Spiraea" (Hardhack shrub) habitat extensively, while redwings use it hardly at all in the marsh. Similarly, redwings are abundant in Scirpus cyperinus (Hairy-seeded Bulrush), whereas wrens seldom use this habitat. Both wrens and redwings use other vegetation types, but redwings use them in the late spring, whereas wrens use them in the summer. Both wrens and redwings have lower reproductive success when nesting in close proximity than when nesting apart. This supports the hypothesis that interspecific competition exists and indicates that selection may favour habitat segregation. I also found mutual suppression of reproductive success when the effects of different vegetation types were removed. The results were not statistically significant however, possibly due to small sample sizes. Of the observed differences between the physical nest site parameters of wrens and redwings, vegetation height and presence and/or depth of water require further investigation as factors in the habitat selection of the two species. Bren-wren competition does not appear to affect wren nesting success in the present study marsh. Management recommendations are given based on the objective of maintaining and possibly enhancing bird species diversity in the study marsh."""@en ; edm:aggregatedCHO "https://circle.library.ubc.ca/rest/handle/2429/21456?expand=metadata"@en ; skos:note "C O M P A R A T I V E H A B I T A T S O F , AMD C O M P E T I T I O N B E T W E E N , THE L O N G - B I L L E D MARSH S E E N AND THE B E D - H I N G E D B L A C K B I R D AT P I T T MEADOWS, B R I T I S H COLOMBIA by C r a i g S t e v e n R u n y a n B . S c , U n i v e r s i t y o f C o l o r a d o , 1970 A T H E S I S SUBMITTED I N P A R T I A L F U L F I L L M E N T OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF S C I E N C E i n THE F A C U L T Y OF GRADUATE S T U D I E S D e p a r t m e n t o f Z o o l o g y We a c c e p t t h i s t h e s i s a s c o n f o r m i n g , t o t h e r e q u i r e d s t a n d a r d THE U N I V E R S I T Y OF B R I T I S H C O L U M B I A M a y , 1979 © C r a i g S t e v e n R u n y a n In presenting th i s thes is in pa r t i a l fu l f i lment of the requirements for an advanced degree at the Un ivers i ty of B r i t i s h Columbia, I agree that the L ibrary sha l l make it f ree l y ava i l ab le for reference and study. I fur ther agree that permission for extensive copying of th is thesis for scho lar ly purposes may be granted by the Head of my Department or by his representat ives. It is understood that copying or pub l i ca t ion of th is thes is for f inanc ia l gain sha l l not be allowed without my writ ten pe rm i ss ion . Department of Zoology The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date April 12, 1979 i i ABSTRACT T h e o b j e c t i v e s o f t h e s t u d y w e r e t o d e t e r m i n e t h e y e a r - r o u n d d i s t r i b u t i o n a n d h a b i t a t s e l e c t i o n o f f o u r m a r s h p a s s e r i n e s p e c i e s , a s d e s c r i b e d by v e g e t a t i o n t y p e a n d i t s p h y s i c a l c h a r a c t e r i s t i c s , a n d t o i n v e s t i g a t e i n t e r s p e c i f i c c o m p e t i t i o n a s a f a c t o r i n t h e h a b i t a t s e l e c t i o n o f t h e L o n g - b i l l e d M a r s h W r e n a n d t h e R e d - w i n g e d B l a c k b i r d . F u l f i l l m e n t o f t h e s e o b j e c t i v e s s h o u l d h e l p t h e B . C . F i s h a n d W i l d l i f e B r a n c h t o a s s e s s t h e e f f e c t s o f t h e i r management p l a n s o n m a r s h p a s s e r i n e s -I d e t e r m i n e d t h e a b u n d a n c e o f f o u r p a s s e r i n e s p e c i e s i n d i f f e r e n t v e g e t a t i o n t y p e s v i a m a r s h c e n s u s t r a n s e c t s o v e r t h e p e r i o d o f one y e a r . N e s t i n g h a b i t a t a n d b r e e d i n g i n f o r m a t i o n o n m a r s h w r e n s a n d r e d w i n g s was o b t a i n e d v i a n e s t s t u d y p l o t s . The r e s u l t s w e r e : - A r e a s t r a v e r s e d f r o m t h e c e n t r a l a n d d e e p e s t m a r s h o u t w a r d t o w a r d s h i g h e r g r o u n d a r e i n h a b i t e d b y r e d w i n g s , m a r s h w r e n s . Common Y e l l o w t h r o a t s , and Song S p a r r o w s , r e s p e c t i v e l y . - H a b i t a t s o f w r e n s a n d r e d w i n g s a r e s p a t i a l l y a n d t e m p o r a l l y s e g r e g a t e d . W r e n s u s e t h e \" D e n s e S p i r a e a \" ( H a r d h a c k s h r u b ) h a b i t a t e x t e n s i v e l y , w h i l e r e d w i n g s u s e i t h a r d l y a t a l l i n t h e m a r s h . S i m i l a r l y , r e d w i n g s a r e a b u n d a n t i n S c i r E U s c y p e r i n u s ( H a i r y -s e e d e d B u l r u s h ) , w h e r e a s w r e n s s e l d o m u s e t h i s h a b i t a t . B o t h w r e n s a n d r e d w i n g s u s e o t h e r v e g e t a t i o n t y p e s , b u t r e d w i n g s u s e t hem i n t h e l a t e s p r i n g , w h e r e a s w r e n s u s e t h e m i n t h e summer . - B o t h w r e n s a n d r e d w i n g s h a v e l o w e r r e p r o d u c t i v e s u c c e s s when n e s t i n g i n c l o s e p r o x i m i t y t h a n when n e s t i n g a p a r t . T h i s s u p p o r t s t h e h y p o t h e s i s t h a t i n t e r s p e c i f i c c o m p e t i t i o n e x i s t s a n d i n d i c a t e s t h a t s e l e c t i o n may f a v o u r h a b i t a t s e g r e g a t i o n . , - I a l s o f o u n d m u t u a l s u p p r e s s i o n o f r e p r o d u c t i v e s u c c e s s when t h e e f f e c t s o f d i f f e r e n t v e g e t a t i o n t y p e s w e r e r e m o v e d . The r e s u l t s w e r e n o t s t a t i s t i c a l l y s i g n i f i c a n t h o w e v e r , p o s s i b l y due t o s m a l l s a m p l e s i z e s . - O f t h e o b s e r v e d d i f f e r e n c e s b e t w e e n t h e p h y s i c a l n e s t s i t e p a r a m e t e r s o f w r e n s a n d r e d w i n g s , v e g e t a t i o n h e i g h t a n d p r e s e n c e a n d / o r d e p t h o f w a t e r r e q u i r e f u r t h e r i n v e s t i g a t i o n a s f a c t o r s i n t h e h a b i t a t s e l e c t i o n o f t h e t w o s p e c i e s . - B r e n - w r e n c o m p e t i t i o n d o e s n o t a p p e a r t o a f f e c t w r e n n e s t i n g s u c c e s s i n t h e p r e s e n t s t u d y m a r s h . Managemen t r e c o m m e n d a t i o n s a r e g i v e n b a s e d on t h e o b j e c t i v e o f m a i n t a i n i n g a n d p o s s i b l y e n h a n c i n g b i r d s p e c i e s d i v e r s i t y i n t h e s t u d y m a r s h . i v T A B L E OF CONTENTS &J&SJTHACT .•••••••••••••••*•••-•••••*•••*•»•••••*/••••'•*••••'••«• 1 i L I S T OF TABLES • <•••••••••**••••••••••••*••••••*• •. • • • V i L I S T OF F I G U R E S . ^ . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . v i i ACKNOWLEDGEMENTS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i x INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 O b j e c t i v e s . . . . . . . . * . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 L i t e r a t u r e R e v i e w . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 R e s e a r c h H y p o t h e s e s . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 METHODS 10 S t u d y A r e a . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 M a j o r P l a n t S p e c i e s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13 I n t r o d u c t i o n And L i m i t a t i o n s O f M e t h o d s . . . . . . . . . . . . . . . . . 24 C e n s u s T r a n s e c t s ............................^.......... . 26 N e s t S t u d y P l o t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 fi£S UIi TS • • •••••••*•••• • • • ******** * ^ 0 G e n e r a l R e s u l t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 S i n t e r H a b i t a t S e l e c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40 C o m p a r a t i v e N e s t i n g I n f o r m a t i o n . . . . . . . . . . . . . . . . . . . . . . . 4 3 P h y s i c a l N e s t S i t e P a r a m e t e r s ............^............ 44 V e g e t a t i o n T y p e S e l e c t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 C e n s u s T r a n s e c t s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 N e s t S u b s t r a t e . . . . . . . . . . . . . . . . . . . • . . . * . . . * , . , , • . . . . . « . 52 S u b s t r a t e U t i l i z a t i o n - Maps O f N e s t P l o t s 61 S u b s t r a t e U t i l i z a t i o n - A n a l y s i s . . . . . . . . . . . . . . . . . . . . 87 Sum HI & IT y • • * • • • • • * • * • • • . 99 C o m p e t . i t . i o n • • • • . 101 H c e n - R e d w i n g . . . . . . » . . . . . . . . . . . . . . . . . . . . . , . . • • • . . • • • - • • • 101 Wren— R r e n . . . . . . . . . . . . . . • • , . » . , . . , . , , . . . . , « , . • • » , . . . . 1 0 8 DXS CO SSXO N . . . . . . • • • • • < » • , • • • . • • « * • • • • . • 113 B i o l o g i c a l I m p l i c a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113 R e v i e w O f H y p o t h e s e s 113 C o m p a r i s o n s W i t h O t h e r S t u d i e s . . . . . . . . . . . . . . . . . . . . . . . . 1 1 4 H a b i t a t S e g r e g a t i o n . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114 C o m p e t i t i o n - - - . - . . - . . , . - • . . . - - - . . . - - - . - • . » . - . . - - - - • • 117 F a c t o r s O t h e r T h a n I n t e r s p e c i f i c C o m p e t i t i o n . . . . . . . . . . 120 F a c t o r s O p p o s i n g S e g r e g a t i o n . . . . . . . . . . . . . . . . . . . . . . ~ . . . 124 C l o s i n g S t a t e m e n t 126 Management I m p l i c a t i o n s . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 127 L I T E B S T O R E C I T E D . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131 A P P E N D I X 135 v i L I S T OF T A B L E S T a b l e I . D i s t r i b u t i o n o f V e g e t a t i o n T y p e s i n T r a n s e c t s 29 T a b l e I I . V e g e t a t i o n A r e a s i n N e s t S t u d y P l o t s . . . . . . . . . 37 T a b l e I I I . C o m p a r a t i v e P h y s i c a l N e s t S i t e P a r a m e t e r s . . . . 4 5 T a b l e I V . N e s t N u m b e r s i n D i f f e r e n t V e g e t a t i o n i n N e s t S t u d y P l o t s 88 T a b l e V . C h r o n o l o g y o f Wren N e s t S u b s t r a t e C h o i c e . . . . . 9 6 T a b l e V I . C h r o n o l o g y o f R e d w i n g S u b s t r a t e C h o i c e . . . . . . . 97 T a b l e V I I . N e s t S u c c e s s v s . v e g e t a t i o n T y p e Osed a s N e s t S u b s t r a t e ....•,,.•>•, M . . . 1 5 , S t u d e n t ' s t ) . , U s i n g t h e d e f i n i t i o n o f a s u c c e s s f u l n e s t a s one p r o d u c i n g a n y n u m b e r o f y o u n g s u r v i v i n g s e v e n o r more d a y s a f t e r h a t c h i n g , I f o u n d t h a t 56% o f a l l w r e n n e s t s (N = 89) a n d 56% o f a l l r e d w i n g n e s t s (N = 39) w e r e s u c c e s s f u l . N e i t h e r s p e c i e s h a d d i f f e r e n t s u c c e s s i n t h e l a t e s p r i n g t h a n i n t h e summer s e a s o n s (p > . 2 0 f o r e a c h s p e c i e s , F i s h e r E x a c t P r o b a b i l i t y ) w 3 . P h y s i c a l N e s t S i t e P a r a m e t e r s The p h y s i c a l c h a r a c t e r i s t i c s o f w r e n n e s t s i t e s a r e d i s t i n c t l y d i f f e r e n t f r o m t h o s e o f r e d w i n g s i t e s ( T a b l e I I I ) . W r e n s p l a c e d t h e i r n e s t s much h i g h e r a n d i n t a l l e r v e g e t a t i o n t h a n r e d w i n g s . T h e g r e a t e r v i s i b i l i t y o f w r e n n e s t s p r o b a b l y r e f l e c t s t h e f a c t t h a t t h e y w e r e p l a c e d h i g h e r o f f t h e g r o u n d a n d i s t h u s o f l i m i t e d u s e a s a c o m p a r a t i v e i n d e x o f v e g e t a t i o n d e n s i t y . Wren n e s t s w e r e p l a c e d o v e r s h a l l o w e r w a t e r o n t h e a v e r a g e t h a n r e d w i n g n e s t s , a n d 43% w e r e o v e r d r y g r o u n d t h r o u g h o u t t h e n e s t ' s a c t i v e p e r i o d , v e r s u s 14% f o r r e d w i n g s ( F i s h e r E x a c t P r o b a b i l i t y = . 0 0 0 1 ) . W r e n s t e n d e d t o p l a c e n e s t s n e a r e r t o v e g e t a t i o n e d g e s t h a n r e d w i n g s . R e d w i n g s o f t e n p l a c e d TABLE III. COMPARATIVE PHYSICAL NEST SITE PARAMETERS Marsh Wren Redwing Significance of Difference Nest* Ht. Nest Visibil ity Veg. Ht. Avg. Water Depth Distance to Veg. Edge Distance to Open Water % of Nests Within .5 m Open Water 92.5 cm ± 2.4** 32.7 cm ± 1.5 12.7 circles ± 0.4 9.1 circles ± 0.5 157.4 cm ± 3.1 6.3 cm (105)*** 5.9 m (115) 8.2 m ••.(90) (100) 97.1 cm ± 2.9 12.5 cm (64) 13.9 m (63) 6.3 m (50) 24% (50) .0000 (Student's t) .0000 (Student's t) .0000 (Student's t) .0000 (Mann-Whitney U) .0000 (Mann-Whitney U) .096 (Mann-Whitney U) .0000 (Fisher Exact Prob.) * See Methods section for definition of parameters ** Standard Error of Mean *** 46 n e s t s i n t h e m i d s t o f e x t e n s i v e S c i r p u s p a t c h e s , w h e r e a s w r e n s o f t e n p l a c e d t h e i r s i n S p i r a e a o r T . l a t i f g l i a v e r y c l o s e t o C a r e x o r S^. c y p e r i n u s p a t c h e s . T h i s i s i n d i r e c t c o n t r a s t t o t h e s t u d y by B u r t ( 1 9 7 0 ) o f a m a r s h w i t h s i m i l a r - s i z e d v e g e t a t i o n p a t c h e s , i n w h i c h 58% o f r e d w i n g n e s t s were w i t h i n 20 f t o f a v e g e t a t i o n e d g e , c o m p a r e d w i t h 35% o f w r e n n e s t s . The a v e r a g e d i s t a n c e t o o p e n w a t e r was s i m i l a r f o r b o t h s p e c i e s , b u t t h e d i s t r i b u t i o n o f t h e d i s t a n c e s s h o w s t h a t a g r e a t e r n u m b e r o f r e d w i n g n e s t s w e r e f o u n d w i t h i n . 5 m o f o p e n w a t e r . Many o f t h e r e d w i n g n e s t s w e r e p l a c e d i n s i n g l e S . c y p e r i n u s p l a n t s s u r r o u n d e d by o p e n w a t e r . O t h e r a u t h o r s ( B u r t 1 9 7 0 , N e r o 1 9 5 6 , W i e n 1965) h a v e a l s o r e c o r d e d a t e n d e n c y f o r r e d w i n g s t o p l a c e n e s t s i n c l o s e p r o x i m i t y t o o p e n w a t e r . 47 V e g e t a t i o n T y p e S e l e c t i o n I n o r d e r t o t e s t t h e - w r e n - r e d w i n g \" S e g r e g a t i o n \" h y p o t h e s i s , I , u s e d t h e r e s u l t s o f t w o m e a s u r e s o f u t i l i z e d v e g e t a t i o n o r h a b i t a t * One m e a s u r e o f u t i l i z e d h a b i t a t was r e l a t i v e a b u n d a n c e i n d i f f e r e n t v e g e t a t i o n t y p e s v i a c e n s u s t r a n s e c t s . T h e o t h e r was t h e n e s t i n g s u b s t r a t e c h o s e n by w r e n s and r e d w i n g s , a s r e c o r d e d i n n e s t s t u d y p l o t s . I p r e s e n t t h e r e s u l t s o f t h e s e t w o m e a s u r e s s e p a r a t e l y w i t h a f i n a l summary o r s y n t h e s i s . C e n s u s t r a n s e c t r e s u l t s f o r y e l l o w t h r o a t s and S o n g S p a r r o w s a r e a l s o p r e s e n t e d . 1. C e n s u s T r a n s e c t s One d i f f e r e n c e b e t w e e n t h e h a b i t a t s o f w r e n s a n d r e d w i n g s i s c l e a r , a n d i t s t a n d s o u t i n b o t h t h e b r e e d i n g ( s p r i n g a n d summer) a n d n o n - b r e e d i n g ( f a l l a n d w i n t e r ) s e a s o n s . Of t h e v e g e t a t i o n t y p e s s a m p l e d by c e n s u s t r a n s e c t s , w r e n s w e r e m o s t a b u n d a n t i n t h e \" D e n s e S p i r a e a \" h a b i t a t , w h i c h was r a r e l y o c c u p i e d by r e d w i n g s ( F i g s . 11 a n d 1 2 ) . * Wrens u s e d p r i m a r i l y h a b i t a t c o n t a i n i n g S p i r a e a w i t h summer a n d f a l l u s e o f S c i r p u s s p p . , w h i l e r e d w i n g s u s e d a l m o s t e x c l u s i v e l y h a b i t a t c o n t a i n i n g s e d g e s ( S c i r p u s s p p . ) . S p i r a e a i s p a r t i c u l a r l y i m p o r t a n t t o w r e n s a s w i n t e r h a b i t a t ( F i g . 1 1 ) . * R e s u l t s o f t h e c e n s u s t r a n s e c t s a r e p r e s e n t e d i n t a b l e f o r m i n t h e A p p e n d i x . 48 F i g u r e 1 1 . N o n - b r e e d i n g S e a s o n M a r s h C e n s u s R e s u l t s b y V e g e t a t i o n T y p e f o r M a r s h Wren a n d R e d - w i n g e d B l a c k b i r d Long - billed Marsh Wren 10 Total Birds k m F * E W LW Dense Spiraea F EW LW Sedge -Spiraea F E W LW s_ acutus F EW LW cyperinus 1 0 h Total Birds km 5r l_J_i F EW LW Red - winged Blackbird UL F EW LW F EW LW F EW LW Dense Spiraea Sedge -Spiraea S. acutus cyperinus ** 'Seasons as defined in methods section : F - F a l l , EW - Early Winter, LW - Late Winter The means of all census transects over the entire fall - winter period were significantly different in different vegetation types for both species ( p * .001 for each species, Kruskal - Wallis one-way analysis of var iance) . 50 F i g u r e 1 2 . B r e e d i n g S e a s o n H a r s h C e n s u s B e s u l t s by V e g e t a t i o n T y p e f o r H a r s h Wren a n d R e d - w i n g e d B l a c k b i r d 51 Males k m 20 15 10 E S * L S S Dense Spiraea Long-billed Marsh Wren _L ES LS S Sedge-Spiraea ES LS S acutus ES LS S _s_ cyperinus Males k m 10 -1_L ES LS S Dense Spiraea Red - winged Blackbird * * ES LS S Sedge -Spiraea ES LS S _s^ acutus i l l ES LS S cyperinus Seasons as defined in methods section: ES - Early Spring, LS - Late Spring, S - Summer The means of all census transects over the entire spring - summer period were significantly different in different vegetation types for both species ( p < 005 for each species, Kruskal - Wallis one - way analysis of variance). 52 T e m p o r a l s e g r e g a t i o n may r e d u c e t h e o v e r l a p i n t h e use o f S . a c u t u s a n d c y p e r i n u s b y t h e two s p e c i e s . Wren a b u n d a n c e i n t h e s e s e d g e s i n c r e a s e s s h a r p l y i n s u m m e r , c o r r e s p o n d i n g w i t h a s t a t i s t i c a l l y i n s i g n i f i c a n t d e c l i n e i n r e d w i n g a b u n d a n c e ( F i g s . 13 a n d 1 4 ) . , S o n g S p a r r o w s a n d y e l l o w t h r o a t s s h a r e h a b i t a t c o n t a i n i n g S p i r a e a w i t h w r e n s a n d a r e m o s t a b u n d a n t i n \" D e n s e S p i r a e a \" ( F i g s . 15 a n d 1 6 ) . T h e y a r e a b s e n t f r o m t h e p u r e s e d g e t y p e s , w i t h t h e e x c e p t i o n o f some f a l l d i s p e r s a l ( F i g . 1 5 ) . , S o n g S p a r r o w s a l s o u t i l i z e d y k e s w i t h s h r u b s b o r d e r i n g some m a r s h a r e a s , a h a b i t n o t s h a r e d t o a n y e x t e n t by wrens , o r y e l l o w t h r o a t s ( B u n y a n 1 9 7 8 ) . , T h e i n c r e a s e i n y e l l o w t h r o a t a b u n d a n c e i n \" D e n s e S p i r a e a \" t h a t t a k e s p l a c e i n summer (p < . 0 5 , M a n n - W h i t n e y 0) c o i n c i d e s w i t h a d e c r e a s e i n w r e n a b u n d a n c e (p < . 0 0 2 , M a n n - W h i t n e y 0 ) . : 2 . N e s t S u b s t r a t e I n t h e f o l l o w i n g s e c t i o n , I show w r e n a n d r e d w i n g n e s t s i t e l o c a t i o n s i n r e l a t i o n t o v e g e t a t i o n i n v e g e t a t i o n c o v e r maps o f t h e s t u d y p l o t s . T h e h a b i t a t s o f w r e n s a n d r e d w i n g s a r e d i s c u s s e d w i t h r e f e r e n c e to , t h e s e m a p s , w i t h m e n t i o n a l s o o f y e l l o w t h r o a t a n d Song S p a r r o w o b s e r v a t i o n s * T h e s u b s e g u e n t s e c t i o n p r o v i d e s a m o r e r i g o r o u s a n a l y s i s o f t h e . i m p o r t a n c e o f t h e d i f f e r e n t v e g e t a t i o n t y p e s f o r w r e n a n d r e d w i n g n e s t i n g s u b s t r a t e . 53 Figure 13. Late Spring and Summer Census Results i n acutus Males km 15 10 Long-billed Marsh Wren (p <.002, Mann - Whitney U ) Late Spring Summer Red-winged Blackbird (p > .31, Mann - Whitney U ) 10 -Males km 5 -Late Spring Summer 55 F i g u r e 14. L a t e S p r i n g a n d Summer C e n s u s R e s u l t s i n S . c y p e r i n u s Males km 10 -Long-billed Marsh Wren (p <.02, Mann - Whitney U ) Late Spring Summer Males km 10 Red-winged Blackbird (p > ! 0 , Mann - Whitney U ) Late Spring Summer 57 F i g u r e 1 5 . N o n - b r e e d i n g S e a s o n M a r s h C e n s u s R e s u l t s b y V e g e t a t i o n T y p e f o r Y e l l o w t h r o a t a n d S o n g S p a r r o w Common Yellowthroat Birds km 5 A 3 2 1 F EW LW * Dense Spiraea F EW LW Sedge -Spiraea F EW LW _s^ acutus F EW LW cyperinus Song Sparrow Birds km 5 A 3 2 1 F EW LW Dense Spiraea F EW LW Sedge -Spiraea EW LW _S_^ acutus EW LW cyperinus Seasons as defined in methods section: F - F a l l , EW - Early Winter, LW - Late Winter 59 F i g u r e 1 6 . B r e e d i n g S e a s o n H a r s h C e n s u s R e s u l t s by V e g e t a t i o n T y p e f o r Y e l l o w t h r o a t a n d S o n g S p a r r o w Common Yellowthroat 10.0 Males k m 5.0 -1 ES LS S * Dense Spiraea ES LS S Sedge-Spiraea ES LS S acutus ES LS S cyperinus 5.0 Males k m Song Sparrow ES LS S Dense Spiraea ES LS S Sedge -Spiraea ES LS S _s, acutus ES LS S cyperinus Seasons as defined in methods section: ES -Ear ly Spring, L S - L a t e Spring, S -Summer 61 a . S u b s t r a t e U t i l i z a t i o n - Haps O f N e s t P l o t s T h e l o c a t i o n o f b r e e d i n g n e s t s i n e a c h o f t h e s i x m a i n n e s t p l o t s i s shown f o r b o t h l a t e s p r i n g a n d summer i n F i g u r e s 1 7 - 2 8 . P l o t C was t h e o n l y p l o t i n w h i c h n e i t h e r s p e c i e s n e s t e d d u r i n g t h e summer s e a s o n * W i t h o n l y one e x c e p t i o n , w ren n e s t s l o c a t e d w i t h i n 10 ra o f one a n o t h e r were n o t s i m u l t a n e o u s l y a c t i v e . P l o t G i s n o t shown b e c a u s e I d i d n o t map o u t i t s v e g e t a t i o n a s r i g o r o u s l y a s t h e o t h e r p l o t s . T h i s 1 ha p l o t of a f a i r l y u n i f o r m m i x t u r e o f T . l a t i f p l j . a a n d S. c y p e r i n u s was one s e c t i o n o f t h e l a r g e s t s i n g l e s t a n d o f T . l a t i f o i i a . w h i c h was more a b u n d a n t i n t h e p l o t t h a n S . c y p e r i n u s , i n t h e PWMA. Wrens a n d r e d w i n g s a p p e a r t o h a v e d i f f e r e n t v e g e t a t i o n p r e f e r e n c e s . W i t h t h e e x c e p t i o n o f c a t t a i l , t h e p r e f e r r e d v e g e t a t i o n o f r e d w i n g s i s s e d g e ( S c i r p u s s p p . ) , w h i l e t h a t o f w r e n s i s t h e S p i r a e a s h r u b . N e s t d i s t a n c e s b e t w e e n t h e t w o s p e c i e s a r e s m a l l e s t whe re S p i r a e a a n d S. c y p e r i n u s meet ( F i g s . 23 a n d 2 4 ) . E e d w i n g n e s t s w e r e a b s e n t f r o m p l o t s c o m p o s e d s o l e l y o f S p i r a e a , , C a r e x s p p . , a n d g r a s s e s ( F i g s . 18 , 19 , a n d 22) . B o t h s p e c i e s n e s t i n T. l a t i f o l i a a n d , t o a l e s s e r e x t e n t , i n a c u t u s > b u t a t d i f f e r e n t t i m e s d u r i n g t h e s e a s o n , Wren s u t i l i z e d b o t h p l a n t s i n t h e summer ( a f t e r J u n e 1 ) , w h i l e r e d w i n g s u t i l i z e d t h e m i n t h e ' l a t e s p r i n g ( F i g s . 2 0 , 2 1 , 2 3 - 2 8 ) . T e m p o r a l s e g r e g a t i o n was p a r t i c u l a r l y a p p a r e n t i n T . l a t i f o l i a . F o u r r e d w i n g n e s t s were f o u n d i n t h e c a t t a i l - d o m i n a t e d P l o t G d u r i n g t h e l a t e s p r i n g s e a s o n when no w r e n s w e r e d e t e c t e d w i t h i n 200 m o f t h e p l o t . One w ren b r e e d i n g n e s t a p p e a r e d much l a t e r i n J u l y . T h o u g h a f e w m a l e and f e m a l e r e d w i n g s w e r e s t i l l s e e n 62 F i g u r e 17. L e g e n d : V e g e t a t i o n C o v e r M a p s , N e s t S t u d y P l o t s Legend: 1. Vegetation + + + + + + + + + • o o • • • n o a n n \" V V V V v v V v v Spiraea douglasii (Hardhack) Graminae spp. Typha latifolia (Broad-leaved Cattail) Scirpus acutus (Hard-stemmed Bulrush) Scirpus cyperinus (Hairy-seeded Bulrush) Carex spp. (Low Sedge) Open Water 2. Breeding Nests Wren • Redwing Scale of maps: 1 cm = 16.7 meter Seasons: Late Spring - prior to June 1 Summer - June 1 and after 64 F i g u r e : 1 8 . B e s t D i s t r i b u t i o n i n P l o t ft. L a t e S p r i n g („5 i v v V V W W v w v v v v v v v v v v w w v w v v v v v v v v v v v v v v v v v V V V V V V v v v v v v v v v v v 70 3, V V V V V V V V W W W W w w w v w w w w v w w v v w w v w w v w v W W W V V W W V V V W V W V v v w w w v v w w w v v w w w v v w w w v v v W V w w w w w w w v V v v w w w w V V V W V V V V V V V w w w w w w w w w V W W V W V V v v w w w 66 F i g u r e 1 9 . N e s t D i s t r i b u t i o n i n P l o t ft. Summer A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A A ) f.tf; „: . i w . -. *.i 0 I 68 F i g u r e 20. B e s t D i s t r i b u t i o n i n P l o t B , L a t e S p r i n g 70 F i g u r e 2 1 . N e s t D i s t r i b u t i o n i n P l o t B , Summer 72 Figure 22- Best Dis t r i b u t i o n i n Plot C, Late Spring 7 3 74 Figure 23. Nest Dis t r i b u t i o n i n Plot D, Late Spring 76 F i g u r e 2 4 . N e s t D i s t r i b u t i o n i n P l o t D , Summer 78 Figure 25. Nest Dis t r i b u t i o n in Plot B, Late Spring 80 Figure 26. Nest Dis t r i b u t i o n i n Plot E, Summer 82 F i g u r e 2 7 . N e s t D i s t r i b u t i o n i n P l o t F , L a t e S p r i n g 84 Figure 28. Nest Distribution i n Plot F, Summer 86 w i t h i n a n d i m m e d i a t e l y a d j a c e n t t o t h e p l o t none o f t h e s e n e s t e d i n t h e p l o t . I n a p a t c h o f T . l a t i f o l i a i n t h e n o r t h e r n c o r n e r o f P l o t D ( F i g s . 23 a n d 2 4 ) , a m a l e w r e n b u i l t a \"dummy\" n e s t ( n o t u s e d f o r b r e e d i n g ) e a r l y i n t h e l a t e s p r i n g . A r e d w i n g t h e n e s t a b l i s h e d a t e r r i t o r y i n w h i c h t w o f e m a l e s n e s t e d , a n d w r e n a c t i v i t y i n t h a t t e r r i t o r y , a n d i n t h e s u r r o u n d i n g a r e a w i t h i n 100 m o f t h e p l o t b o u n d a r y , c e a s e d u n t i l l a t e J u n e , a f t e r t h e b l a c k b i r d s c o m p l e t e d t h e i r n e s t i n g . y e l l o w t h r o a t s a n d S o n g S p a r r o w s w e r e a l s o d e t e c t e d i n t h e p l o t s , p r i m a r i l y i n S p i r a e a s t a n d s ( P l o t s A a n d C ) . T h o u g h we f o u n d n o n e s t s , we o b s e r v e d r e c e n t l y f l e d g e d y e l l o w t h r o a t y o u n g i n t h e p l o t s on t h r e e o c c a s i o n s . One S o n g S p a r r o w n e s t was l o c a t e d i n P l o t C . T e r r i t o r i e s o f y e l l o w t h r o a t s a n d w r e n s d e t e r m i n e d by t h e l o c a t i o n s o f m a l e s o n g , a p p e a r e d t o be s e g r e g a t e d . Wrens n e s t i n g i n t h e S p i r a e a o f A a n d C n o r m a l l y c h o s e s i t e s b e s i d e C a r e x p a t c h e s i n t h e e a s t e r n p o r t i o n o f A a n d t h e s o u t h e r n p o r t i o n o f C . Y e l l o w t h r o a t s e s t a b l i s h e d m o s t o f t h e i r t e r r i t o r i e s i n t h e w e s t e r n a n d n o r t h e r n p a r t s o f A a n d C r e s p e c t i v e l y , w h e r e g r a s s e s were more a b u n d a n t , a n d t h e g r o u n d was n o t i c e a b l y h i g h e r . 87 b. S u b s t r a t e U t i l i z a t i o n - A n a l y s i s How important are the d i f f e r e n t v e g e t a t i o n types to redwings and wrens as n e s t i n g s u b s t r a t e ? To answer that question, I examined the percentages of a l l n e s t s i n each of the p l a n t s p e c i e s (Table IV) weighted by d i v i d i n g by the area of t h a t p l a n t s p e c i e s covered (Fig- 29). When c o n s i d e r i n g the e n t i r e breeding season, Spiraea h a b i t a t was much more important to wrens than t o redwings, and the two S c i r p u s spp. were more important t o redwings than to wrens ( F i g . 29). I observed the same r e l a t i o n s h i p i n the a n a l y s i s o f census t r a n s e c t s ( F i g - 12). Typha was the most important p l a n t used f o r nest s u b s t r a t e f o r both redwings and wrens. By s e p a r a t i n g t h e a n a l y s i s i n t o the l a t e s p r i n g and summer ne s t i n g seasons ( F i g s . 30 ad 31), temporal s e g r e g a t i o n emerges. Wrens use T. l a t i f o l i a and S. acutus p r i m a r i l y i n the summer when the redwing use has decreased. The r e s u l t s of census t r a n s e c t s suggested t h i s same temporal s e g r e g a t i o n i n the use of S«. acutus and c y p e r i n u s ( F i g - 12). Wrens r a r e l y used S. c y p e r i n u s as n e s t i n g s u b s t r a t e , and there was no temporal s e g r e g a t i o n from redwings i n t h i s v e g e t a t i o n type ( F i g s . 30 and 31). I t h i n k the main reason f o r t h i s d i s c r e p a n c y between the census t r a n s e c t r e s u l t s and the n e s t s u b s t r a t e r e s u l t s f o r S. c y p e r i n u s i s that the t o t a l census t r a n s e c t sample s i z e f o r S. c y p e r i n u s was r e l a t i v e l y s m a l l (see Table I ) . TABLE IV. NEST NUMBERS IN DIFFERENT VEGETATION IN NEST STUDY PLOTS Spiraea douglasii S. acutus S. cyperinus T. latifolia Carex spp. Total Wren Total 57 nests* 16 5 27 0 105 Late Spring 41 3 0 6 50 Summer 16 13 5 21 55 Redwing Total 1* 20 22 14 2 59 Late Spring 1 18 6 13 2 40 Summer 0 2 16 1 0 19 Nests containing eggs or young 89 Figure 29. Weighted Nest Distributions by Vegetation, Entire Season K.O 12.0 °/o 10.0 Nests in Vegetation Area Vegetation (ha) 8.0 6.0 A.O 2.0 Wren Redwing Spiraea S. acutus S. cyperinus Typha 91 Figure 30- Weighted Nest Distributions by Vegetation, Late Spring 24.0 Nests in Vegetation Area Vegetation (ha) 16.0 12.0 8.0 4.0 Wren Redwing Spiraea S. acutus S. cyperinus Typha 9 3 F i g u r e 3 1 . w e i g h t e d N e s t D i s t r i b u t i o n s b y V e g e t a t i o n , Summer 24.0 0 / 20.0 Nests in Vegetation Area Vegetation (ha) 16.0 12.0 8.0 4.0 Redwing Wren Spiraea S. acutus S. cyperinus Typha 95 S e v e r a l a u t h o r s e m p h a s i z e t h e i m p o r t a n c e o f e x a m i n i n g t h o s e h a b i t a t s i n w h i c h s e x u a l p a i r i n g o c c u r s f i r s t a s a n i n d i c a t i o n o f s u i t a b i l i t y o f t e r r i t o r i e s ( S v a r d s o n 1 9 4 9 , V e r n e r 1964 a n d 1 9 7 5 b ) . T h e n u m b e r s i n T a b l e s V a n d V I r e p r e s e n t t h i s same i d e a i n t e r m s o f t h e o r d e r i n w h i c h d i f f e r e n t s u b s t r a t e s a r e c h o s e n f o r b r e e d i n g n e s t s . . F i v e - d a y t i m e i n t e r v a l s w e r e e x a m i n e d , s t a r t i n g f r o m t h e d a t e o f t h e f i r s t c o m p l e t e c l u t c h b y e a c h s p e c i e s , a n d t h e n u m b e r o f n e s t s i n e a c h s u b s t r a t e was w e i g h t e d fey t h e s u b s t r a t e a r e a s a m p l e d . W r e n s c h o s e S p i r a e a f i r s t w h i l e r e d w i n g s c h o s e Ty p h a , a r e s u l t c o n s i s t e n t w i t h t h e o v e r a l l s u b s t r a t e u s a g e f o r t h e l a t e s p r i n g s e a s o n ( F i g . 3 0 ) . T h o u g h t h e o v e r a l l d i f f e r e n c e i n n e s t i n g s u c c e s s b e t w e e n n e s t s i n d i f f e r e n t v e g e t a t i o n t y p e s i s s i g n i f i c a n t o n l y f o r r e d w i n g n e s t s (p < . 0 5 , C h i - s g u a r e d ) , t h e r e i s a n i n d i c a t i o n t h a t b o t h w r e n s a n d r e d w i n g s h a d t h e g r e a t e s t n e s t i n g s u c c e s s i n t h e t w o s u b s t r a t e s t h e y u s e d m o s t o f t e n a n d t h e l e a s t s u c c e s s i n S . a c u t u s ( T a b l e V I I ) . F l o o d i n g c a u s e d f i v e o f t h e e i g h t r e d w i n g f a i l u r e s i n S . a c u t u s , a n d t h i s c a u s e o f n e s t f a i l u r e a l o n e s u f f i c i e n t l y e x p l a i n s t h e d i f f e r e n c e i n r e d w i n g n e s t i n g s u c c e s s i n d i f f e r e n t v e g e t a t i o n t y p e s . » F l o o d i n g a l s o c a u s e d t h e f a i l u r e o f one o f t w o r e d w i n g n e s t s p l a c e d i n C a r e x s i t c h e n s i s . A l l o f t h e 11 w r e n n e s t s i n S . a c u t u s w e r e l o c a t e d i n n e s t P l o t B , a n d s i x o f t h e s e v e n f a i l u r e s w e r e a s s o c i a t e d w i t h e x t e n s i v e n e s t d e s t r u c t i o n . T h i s d e s t r u c t i o n r a n g e d f r o m a l a r g e h o l e i n t h e n e s t , t o t h e m i s s h a p e n n e s t b e i n g f o u n d i n t h e w a t e r a s i f * I f f l o o d e d r e d w i n g n e s t s i n S . a c u t u s a r e i g n o r e d , t h e d i f f e r e n c e s i n T a b l e V I I a r e n o l o n g e r s t a t i s t i c a l l y s i g n i f i c a n t f o r e i t h e r s p e c i e s * 96 TABLE V. CHRONOLOGY OF WREN NEST SUBSTRATE CHOICE 1st 5 days 2nd 5 days 3rd 5 days Spi raea douglasi i _S. acutus T. latifolia * (No. nests in veg. type/Area veg. type sampled) x 10 nests ha x 10 4.5 6.1 2.8 5.6 TABLE VI. CHRONOLOGY OF REDWING SUBSTRATE CHOICE 1st 5 days 2nd 5 days 3rd 5 days S. acutus nests ha x 10 4.2 4.2 cyperinus 2.1 2.1 6.2 T. latifolia 5.6 16.7 38.9 * (No. nests in veg. type/Area veg. type sampled) x 10 93 TABLE V I I . NEST SUCCESS VS. VEGETATION TYPE USED AS NEST SUBSTRATE Spiraea douglasi i S_. acutus S_. cyperinus X- l a t i f o l i a 51%* 36% insu f f i c i en t g g % W r e n (N = 47) (N = 11) ' ( ^ = 5 ) ( N = 2 9 ) i n su f f i c i en t sample (N = 1) 75% 56% Redwing sample ( N ^ ' l l ) (N =°16) (N=°9 ) * Percentage of nests in that vegetation type succeeding in fledging one or more young. 99 i t , a n d t h e s t e m t o w h i c h i t was a t t a c h e d , had b e e n p u s h e d d o w n . A l a r g e p r e d a t o r , s u c h a s t h e e v e r p r e s e n t N o r t h w e s t e r n C r o w , i s s u s p e c t e d . 3. Summary Wrens u s e d i f f e r e n t v e g e t a t i o n t y p e s t h a n t h o s e t y p e s u s e d by r e d w i n g s , o r t h e same t y p e s b u t a t d i f f e r e n t t i m e s . T h i s r e s u l t was c o n s i s t e n t f o r t w o m e t h o d s u s e d d u r i n g t h e s p r i n g a n d summer s e a s o n s : c e n s u s t r a n s e c t s t h a t c e n s u s e d s i n g i n g m a l e s a n d n e s t c o u n t s i n n e s t s t u d y p l o t s . T h i s s u p p o r t s t h e \" S e g r e g a t i o n \" h y p o t h e s i s . W r e n s a p p e a r t o p r e f e r h a b i t a t c o n t a i n i n g S p i r a e a , w i t h t h e e x c e p t i o n o f a p r e f e r e n c e f o r T . l a t i f o l i a d u r i n g summer n e s t i n g . R e d w i n g s p r e f e r S c i r p u s s p p . , w i t h t h e e x c e p t i o n o f t h e l a t e s p r i n g , when t h e y p r e f e r T . l a t i f o l i a f o r n e s t i n g . T h e y r a r e l y u s e t h e \" D e n s e S p i r a e a \" h a b i t a t p r e f e r r e d b y w r e n s . B o t h w r e n s a n d r e d w i n g s u t i l i z e d S . a c u t u s a n d T . l a t i f o l i a . b u t a t d i f f e r e n t t i m e s . T h i s t e m p o r a l s e g r e g a t i o n t o o k t h e f o r m o f r e d w i n g u s e f i r s t , f o l l o w e d by w r e n u s e , f o r b o t h h a b i t a t s . A s s h o w n i n o t h e r s t u d i e s , T y p h a i s i m p o r t a n t a s n e s t i n g s u b s t r a t e f o r b o t h s p e c i e s , b o t h i n r e l a t i v e u s e a n d n e s t i n g s u c c e s s . I d i d n o t e x a m i n e t h e w i n t e r u s e o f t h e T y p h a h a b i t a t . S o n g S p a r r o w s a n d y e l l o w t h r o a t s s h a r e t h e s h r u b p o r t i o n o f , t h e : w r e n ' s h a b i t a t , a n d a p a t t e r n o f v e g e t a t i o n u s e b y t h e f o u r p a s s e r i n e s p e c i e s i n r e l a t i o n t o s u c c e s s i v e s t a g e s f r o m t h e c e n t r a l m a r s h a p p e a r s . A r e a s t r a v e r s e d f r o m t h e c e n t r a l a n d d e e p e s t m a r s h o u t w a r d t o w a r d s h i g h e r g r o u n d , a r e i n h a b i t e d by r e d w i n g s , w r e n s , y e l l o w t h r o a t s , a n d S o n g S p a r r o w s i n t h a t o r d e r . 100 A l l e n ( 1914 ) r e p o r t s a s i m i l a r p a t t e r n . 101 Compe t i t i on I n t h i s s e c t i o n , I p r e s e n t t h e r e s u l t s o f t e s t s o f t h e t w o r e s e a r c h h y p o t h e s e s t h a t e x a m i n e t h e r o l e o f i n t e r f e r e n c e c o m p e t i t i o n i n t h e h a b i t a t s e l e c t i o n o f w r e n s a n d r e d w i n g s . 1. W r e n - B e d w i n g I e x a m i n e d t h e e f f e c t o f w r e n - r e d w i n g n e s t d i s t a n c e on t h e n e s t i n g s u c c e s s o f e a c h s p e c i e s . S i n c e i n d i v i d u a l w r e n s a n d r e d w i n g s n o r m a l l y m a i n t a i n r o u g h l y t h e same t e r r i t o r y t h r o u g h o u t t h e b r e e d i n g p e r i o d ( V e r n e r 1 9 6 5 a , K a l e 1 9 6 5 , A l i e n 1 9 1 4 , B e n t 1958) t, t h e w r e n - r e d w i n g n e s t d i s t a n c e f o r a n y n e s t was d e f i n e d a s t h a t b e t w e e n i t a n d a n y b r e e d i n g n e s t o f t h e o t h e r s p e c i e s w h i c h i s a c t i v e a n y t i m e b e f o r e , d u r i n g , o r up t o t w o weeks f o l l o w i n g t h e a c t i v e p e r i o d o f t h e n e s t i n q u e s t i o n . I e x c l u d e d f l o o d e d r e d w i n g n e s t s f r o m t h e a n a l y s i s o f r e d w i n g n e s t i n g s u c c e s s . The d i s t r i b u t i o n s o f n e s t s u c c e s s e s a n d f a i l u r e s a t d i f f e r e n t min imum w r e n - r e d w i n g n e s t d i s t a n c e s ( F i g s . 32 a n d 3 3 ) * s u g g e s t t h a t w r e n s a n d r e d w i n g s h a v e l o w e r s u c c e s s a t w r e n -r e d w i n g d i s t a n c e s c l o s e r t h a n 50 m a n d 25 m r e s p e c t i v e l y . I n d i v i d u a l s o f b o t h s p e c i e s d o , i n f a c t , h a v e s i g n i f i c a n t l y l o w e r s u c c e s s when t h e y n e s t c l o s e r t o i n d i v i d u a l s o f t h e o t h e r s p e c i e s t h a n t h e s e s u g g e s t e d c u t - o f f p o i n t s ( T a b l e s V I I I a n d I X ) . , T h i s s u p p o r t s t h e \" W r e n - B e d w i n g C o m p e t i t i o n \" h y p o t h e s i s . * The s c a l e o n t h e x - a x i s o f F i g u r e 32 i s l a r g e r t h a n t h a t o f F i g u r e 33 b e c a u s e t h e t e r r i t o r y , a n d t h u s t h e a r e a o f i n f l u e n c e , o f a w r e n i s n o r m a l l y much s m a l l e r t h a n t h a t o f a r e d w i n g . 102 Figure 32. D i s t r i b u t i o n of Redwing Nest outcome with Respect to I n t e r s p e c i f i c Distance Failure Success 2 2 1 nest 1 1 1 2 1 _ l I I I I , L_ 1 1— 10 20 30 AO 50 60 70 80 Distance to Nearest Wren Breeding Nest (m) 104 F i g u r e 33. D i s t r i b u t i o n of Wren Nest Outcome w i t h Bespect to I n t e r s p e c i f i c D i s t a n c e Failure 2 nests 1 1 2 1 1 1 1 1 2 1 Success 1 122 1 2 1 1 1 3 1 1 1 _ i i i i i i i i i i i i 1— 10 20 30 40 50 60 70 80 90 100 110 120 130 Distance to Nearest Redwing Nest ( m ) TABLE VIII. CLOSEST REDWING NEST DISTANCE CATEGORY VS. WREN NEST SUCCESS Redwing Nest Distance < 50 m > 50 m Wren 13 nests 18 Success (50%) (75%) Wren 13 6 Failure (50%) (25%) Total 26 24 Statistics: Accept differences in nest success at .05 level (Fisher Exact Probability of null hypothesis = .03) TABLE IX. CLOSEST MARSH WREN NEST DISTANCE VS. REDWING NEST SUCCESS Wren Nest Distance < 25 m >25 m Redwing 2 nests 13 Success (28.6%) (72.2%) Redwing 5 5 Failure (71.4%) (27.8%) Total 7 18 Statistics: Accept differences in nest success at .05 level (Fisher Exact Probability of null hypothesis = .03) 108 The n a t u r e o f r e d w i n g n e s t f a i l u r e s c l o s e t o w r e n n e s t s s u p p o r t s t h e i d e a t h a t w r e n s w e r e t h e c a u s e . None o f t h e f o u r r e d w i n g n e s t s t h a t w e r e c l o s e r t h a n 15 m t o a w r e n n e s t s u c c e e d e d . Two o f t h e s e n e s t s w e r e i n T . l a t i f o l i a , a n d two w e r e i n c y p e r i n u s , p l a n t s i n w h i c h r e d w i n g s w e r e , on t h e a v e r a g e , more s u c c e s s f u l ( T a b l e V I I ) . E g g s o r y o u n g were m i s s i n g f r o m a l l f i v e o f t h e f a i l e d n e s t s c l o s e r t h a n 25 m t o a w r e n n e s t , and I f o u n d t w o b r o k e n e g g s on t h e g r o u n d b e n e a t h o n e o f t h e n e s t s . None o f t h e s e n e s t s h a d b e e n o b v i o u s l y d i s r u p t e d ( t i l t e d , n e s t m a t e r i a l d i s r u p t e d , o r f a l l e n d o w n ) . E v i d e n c e f o r t h e c a u s e o f t h e 13 w r e n n e s t f a i l u r e s c l o s e t o n e s t s o f r e d w i n g s was i n c o n c l u s i v e - A l l o f t h e s e n e s t s l o s t e g g s o r y o u n g , a n d 6 o f t h e 13 w e r e o b v i o u s l y d i s r u p t e d ( t o p o f n e s t m i s s i n g o r n e s t k n o c k e d d o w n ) . T h i s p a t t e r n o f m u t u a l s u p p r e s s i o n o f n e s t i n g s u c c e s s i s a l s o f o u n d when t h e e f f e c t s o f d i f f e r e n t v e g e t a t i o n t y p e s on n e s t i n g s u c c e s s a r e r e m o v e d ( T a b l e X ) . T h e r e s u l t s a r e , h o w e v e r , s t a t i s t i c a l l y i n s i g n i f i c a n t , p o s s i b l y due t o l o w s a m p l e s i z e s . T h u s , t h e r e l a t i o n s h i p b e t w e e n v e g e t a t i o n a n d i n t e r s p e c i f i c e f f e c t s on n e s t i n g s u c c e s s r e m a i n s u n r e s o l v e d . 2 . W r e n - W r e n O v e r a l l , w r e n - w r e n c o m p e t i t i o n d o e s n o t a p p e a r t o a f f e c t t h e o u t c o m e o f w r e n n e s t s . C o n s i d e r i n g a l l w r e n n e s t s , t h e d i s t a n c e b e t w e e n a n e s t a n d t h a t o f t h e c l o s e s t c o n s p e c i f i c n e s t t h a t i s s i m u l t a n e o u s l y a c t i v e d o e s n o t a f f e c t t h e s u c c e s s o f t h e n e s t ( T a b l e X I ) . 109 TABLE X. MUTUAL SUPRESSION OF NESTING SUCCESS IN DIFFERENT VEGETATION TYPES % Success Stati sti cal Vegetation • Significance Species Type Used Small* Large (Fisher Exact For Nesting Interspecific Interspecific Distances Di stances Probability) Redwing S. cyperinus 33.3% 80.0% (3)** (10) .10 T. latifolia 25.0% 66.7% .18 (4) (3) Wren Spiraea 33.3% 68.4% .07 (6) (19) T. latifolia 53.3% 100% .10 (15) (3) * Cutoff points are 25 m and 50 m for redwing and wren nests respectively * Sample size TABLE XI. CLOSEST WREN NEST DISTANCE VS. WREN NEST SUCCESS FOR ALL NESTS Wren Nest Distance 25 m* > 25 m Wren 17 nests 26 Success (68%) (54.2%) Wren 8 22 Failure (32%) (45.8%) Total 25 48 Statistics: p = .19, Fisher Exact Probability * The use of other cut-off points yielded similar results 111 S i m i l a r l y , s m a l l w r e n - w r e n n e s t d i s t a n c e was n o t r e l a t e d t o n e s t s u c c e s s , e v e n when r e d w i n g n e s t s w e r e w i t h i n 50 m, t h e d i s t a n c e p r e v i o u s l y d e t e r m i n e d t o b e t h e r a d i u s o f i n f l u e n c e o f r e d w i n g s on w r e n s ( T a b l e X I I ) - - I n f a c t , t h e r e s u l t s , t h o u g h n o t s i g n i f i c a n t , s u g g e s t t h a t s m a l l w r e n - w r e n n e s t d i s t a n c e s a r e a s s o c i a t e d w i t h g r e a t e r n e s t i n g s u c c e s s t h a n l a r g e r d i s t a n c e s . , T h i s w o u l d be j u s t t h e o p p o s i t e f r o m t h e r e s u l t p r e d i c t e d by t h e \" W r e n - W r e n C o m p e t i t i o n \" h y p o t h e s i s , w h i c h c a n n o t t h e r e f o r e b e a c c e p t e d . 112 TABLE XII. CLOSEST WREN NEST DISTANCE VS. WREN NEST SUCCESS FOR NESTS CLOSER THAN 50 M FROM A REDWING NEST Wren Nest Distance < 25 m > 25. m Wren 6 nests 7 Success (60%) (46.7%) Wren 4 8 Failure (40%) (53.3%) Total 10 15 Statistics: p = .40, Fisher Exact Probability 113 D I S C U S S I O N B i o l o g i c a l I m p l i c a t i o n s 1- R e v i e w O f H y p o t h e s e s I n t h i s s t u d y I e v a l u a t e d t h r e e h y p o t h e s e s a b o u t c o m p a r i s o n s b e t w e e n w r e n s a n d r e d w i n g s . F i r s t , b e c a u s e t h i s s t u d y m a r s h c o n t a i n s a u n i q u e d i v e r s i t y o f v e g e t a t i o n , i n t h e \" S e g r e g a t i o n \" H y p o t h e s i s , I h y p o t h e s i z e d t h a t w r e n s a n d r e d w i n g s w o u l d be s e g r e g a t e d by t h e use o f d i f f e r e n t v e g e t a t i o n t y p e s o r t h e same t y p e s b u t a t d i f f e r e n t t i m e s . T h e r e s u l t s o f t w o d i f f e r e n t s t u d y m e t h o d s s u p p o r t e d t h i s h y p o t h e s i s . The g r e a t e s t d e g r e e o f s e g r e g a t i o n was e x h i b i t e d i n t h e c o n t r a s t i n g r e s u l t s t h a t w r e n s w e r e mos t a b u n d a n t i n h a b i t a t c o n t a i n i n g d e n s e s t a n d s o f t h e s h r u b S p i r a e a d o u g l a s i i a n d t h a t r e d w i n g s w e r e r a r e l y f o u n d i n t h i s h a b i t a t . S e c o n d , o f t h e p o s s i b l e u l t i m a t e f a c t o r s ( H i l d e n 1965) t h a t i n f l u e n c e t h e h a b i t a t s e l e c t i o n o f w r e n s a n d r e d w i n g s , I c h o s e t o e x a m i n e i n t e r s p e c i f i c c o m p e t i t i o n , a s d e f i n e d b y t w o s p e c i e s h a v i n g a n e g a t i v e e f f e c t on one a n o t h e r { M a c f t r t h u r 1 9 7 2 ) . T h e r e s u l t s o f m o n i t o r i n g n e s t i n g s u c c e s s i n r e l a t i o n t o i n t e r s p e c i f i c n e s t d i s t a n c e s s u p p o r t e d t h i s h y p o t h e s i s , w h i c h s t a t e s t h a t c l o s e r i n t e r s p e c i f i c d i s t a n c e s a r e r e l a t e d t o l o w e r n e s t i n g s u c c e s s f o r b o t h s p e c i e s . S h e n t h e e f f e c t s o f d i f f e r e n t v e g e t a t i o n t y p e s on n e s t i n g s u c c e s s w e r e r e m o v e d , I o b s e r v e d t h e same r e l a t i o n s h i p b e t w e e n i n t e r s p e c i f i c d i s t a n c e s a n d n e s t s u c c e s s . The r e s u l t s o f t h e l a t e r a n a l y s i s , h o w e v e r , were n o t s i g n i f i c a n t s t a t i s t i c a l l y , p o s s i b l y due t o l o w s a m p l e s i z e s . 114 The t h i r d h y p o t h e s i s s t a t e s : \" W r e n n e s t i n g f a i l u r e , f o r n e s t s l o c a t e d c l o s e r t o r e d w i n g n e s t s , i s r e l a t e d t o s m a l l w r e n -w r e n d i s t a n c e s . \" I n t h i s h y p o t h e s i s , I e x a m i n e d t h e p o s s i b i l i t y t h a t h a r a s s m e n t o f w r e n s by r e d w i n g s c o u l d c a u s e w r e n s t o n e g l e c t t h e i r n e s t s , l e a v i n g t h e s e n e g l e c t e d n e s t s more v u l n e r a b l e t o i n t r a s p e c i f i c n e s t d e s t r u c t i o n , fly r e s u l t s d i d n o t s u p p o r t t h i s h y p o t h e s i s , n o r w e r e s m a l l i n t r a s p e c i f i c n e s t d i s t a n c e s , t a k i n g a l l w r e n n e s t s i n t o a c c o u n t , a s s o c i a t e d w i t h l o w w r e n n e s t i n g s u c c e s s . 2 . C o m p a r i s o n s W i t h O t h e r S t u d i e s a . H a b i t a t S e g r e g a t i o n I t i s s u r p r i s i n g t h a t w r e n n e s t s w e r e mos t a b u n d a n t i n t h e s h r u b . S p i r a e a ( a l o n g w i t h c a t t a i l i n t h e summer o r l a t e r ; n e s t i n g s e a s o n ) a n d t h a t r e d w i n g s r a r e l y u s e d S p i r a e a a s n e s t i n g s u b s t r a t e . I f r e d w i n g s a r e e v o l u t i o n a r i l y more r e c e n t m a r s h i n h a b i t a n t s t h a n w r e n s ( A l i e n 1 9 1 4 , B u r t 1 9 7 0 ) , o n e w o u l d e x p e c t w r e n s t o be b e t t e r a d a p t e d t o n e s t i n g i n s e d g e ( p r i m a r i l y S c i r p u s a n d C a r e x s p p . ) a n d c a t t a i l , w h i c h t y p i f y m a r s h v e g e t a t i o n , t h a n a r e r e d w i n g s . The d i v e r s i t y o f r e d w i n g n e s t i n g s u b s t r a t e ( B e n t 1958) a n d t h e r e d w i n g ' s a d a p t a b i l i t y t o a w i d e r r a n g e o f h a b i t a t s ( u p l a n d a s w e l l a s marsh ) t h a n t h a t o f w r e n s a l s o s u g g e s t t h a t r e d w i n g s w o u l d be more l i k e l y t o u s e s h r u b s t h a n w r e n s . T h e r e s u l t s o f o t h e r s t u d i e s may h e l p e x p l a i n why t h i s was n o t t h e c a s e a n d p u t t h e h a b i t a t s e g r e g a t i o n I o b s e r v e d i n t o a b r o a d e r p e r s p e c t i v e . 115 O f t h e few p r e v i o u s s t u d i e s i n v o l v i n g w r e n s a n d r e d w i n g s , B u r t (1970 — T h i s a n d a l l s u b s e q u e n t r e f e r e n c e s t o B u r t a r e b a s e d o n h i s 1970 M . S c . t h e s i s . ) a n d P i e m a n ( T h i s a n d a l l s u b s e q u e n t r e f e r e n c e s t o P i e m a n a r e b a s e d on h i s P h . D . t h e s i s i n p r o g r e s s , u n l e s s o t h e r w i s e s t a t e d . ) p r o v i d e t h e m o s t e x t e n s i v e c o m p a r a t i v e i n f o r m a t i o n o n t h e t w o s p e c i e s . , B u r t ' s I o w a s t u d y m a r s h c o n t a i n e d a v a r i e t y o f s e d g e v e g e t a t i o n d i s t r i b u t e d i n p a t c h e s s i m i l a r i n s i z e t o t h e p a t c h e s i n t h e p r e s e n t s t u d y m a r s h , a n d he o b s e r v e d e x t e n s i v e o v e r l a p i n t h e t y p e s o f v e g e t a t i o n u s e d f o r n e s t i n g by w r e n s a n d r e d w i n g s . T h i s was p a r t i c u l a r l y t r u e i n t h o s e p o r t i o n s o f t h e s t u d y a r e a i n w h i c h Y e l l o w - h e a d e d B l a c k b i r d s were p r e s e n t . I n t h e l a r g e s t p o r t i o n o f B u r t ' s m a r s h , i n w h i c h w r e n s , r e d w i n g s , and y e l l o w h e a d s n e s t e d i n t h e l a r g e s t n u m b e r s , 96% o f a l l w r e n n e s t s a n d 52% o f a l l r e d w i n g n e s t s w e r e p l a c e d i n C a r e x l a c u s t r i s ( L a k e s e d g e ) . T h u s , t h e d e g r e e o f s e g r e g a t i o n , a s m e a s u r e d by o v e r l a p i n t h e t y p e s o f v e g e t a t i o n u s e d f o r n e s t i n g s u b s t r a t e i s much s m a l l e r i n B u r t ' s s t u d y t h a n i n m i n e . The p r e s e n c e o r a b s e n c e o f y e l l o w h e a d s , h o w e v e r , may b e a c r u c i a l f a c t o r when c o m p a r i n g t h e h a b i t a t s o f w r e n s a n d r e d w i n g s . Y e l l o w h e a d s a r e o n l y p r e s e n t i n my s t u d y m a r s h i n t h e f o r m o f a s m a l l ( 6 - 1 2 i n d i v i d u a l s ) c o l o n y , a n d i t i s u n l i k e l y t h a t t h e c o l o n y a f f e c t s w r e n o r r e d w i n g d i s t r i b u t i o n s . The c o l o n y , t h o u g h s e e n i n o t h e r l o c a t i o n s o f my m a r s h , w a s n e v e r s e e n i n my n e s t s t u d y p l o t s . T h e r e i s s u b s t a n t i a l e v i d e n c e s u p p o r t i n g t h e i d e a t h a t y e l l o w h e a d s a f f e c t b o t h r e d w i n g a n d w r e n d i s t r i b u t i o n s . I n B u r t ' s s t u d y , a l t h o u g h t h e h a b i t a t o f w r e n s a n d r e d w i n g s o v e r l a p p e d e x t e n s i v e l y i n t h e p r e s e n c e o f y e l l o w h e a d s , r e d w i n g s 116 a n d w r e n s s h o w e d m a r k e d s e g r e g a t i o n a f t e r y e l l o w h e a d s c o m p l e t e d t h e i r r e l a t i v e l y s h o r t n e s t i n g p e r i o d . B e d w i n g s e s t a b l i s h e d t h e m s e l v e s i n c a t t a i l p a t c h e s f o r m e r l y o c c u p i e d b y y e l l o w h e a d s , w h i l e w r e n s , a f t e r a n i n i t i a l movement i n t o t h e c a t t a i l , r e t u r n e d t o t h e l a k e s e d g e . T h i s s u g g e s t s t h a t r e d w i n g s w e r e e x c l u d e d f r o m h a b i t a t by y e l l o w h e a d s , an i d e a a l s o s u g g e s t e d b y H i l l e r ( 1 9 6 8 ) . B u r t , H e r o (1956) , a n d H i e n (1965) a l l p r o v i d e e v i d e n c e t h a t a \" t y p i c a l \" f e a t u r e ( a s s o c i a t i o n w i t h o p e n w a t e r ) o f y e l l o w - h e a d e d h a b i t a t i s p r e f e r r e d b y r e d w i n g s i n t h e a b s e n c e o f y e l l o w h e a d s . B u r t ' s r e s u l t s a l s o s u g g e s t t h a t , i n m a r s h e s f r o m w h i c h y e l l o w h e a d s a r e a b s e n t , r e d w i n g s e x c l u d e w r e n s f r o m c e r t a i n t y p e s o f h a b i t a t i n a manner s i m i l a r t o t h e e x c l u s i o n o f w r e n s a n d r e d w i n g s by y e l l o w h e a d s i n o t h e r m a r s h e s . T h i s c o u l d e x p l a i n t h e more m a r k e d s e g r e g a t i o n b e t w e e n t h e t w o s p e c i e s i n my m a r s h , w h e r e y e l l o w h e a d s do n o t r e s t r i c t t h e i r r a n g e o f h a b i t a t , t h a n i n B u r t ' s m a r s h . A l s o , t h e s t r o n g a f f i n i t y f o r c e n t r a l m a r s h l o c a t i o n s c o u l d o v e r r i d e o t h e r f a c t o r s i n e x p l a i n i n g t h e r e d w i n g ' s r e l a t i v e a b s e n c e f r o m t h e more p e r i p h e r a l S p i r a e a h a b i t a t i n my m a r s h . The h y p o t h e s i s t h a t r e d w i n g s e x c l u d e w r e n s f r o m h a b i t a t c o u l d be t e s t e d i n t h e f i e l d b y e x p e r i m e n t a l l y r e m o v i n g r e d w i n g s f r o m s e d g e v e g e t a t i o n a n d o b s e r v i n g t h e s u b s e q u e n t d i s t r i b u t i o n o f w r e n s . P i e m a n , w h o s e r e s e a r c h t o o k p l a c e i n a b r a c k i s h , f o r e s h o r e m a r s h t h a t i s q u i t e d i f f e r e n t f r o m b o t h B u r t ' s a n d my s t u d y m a r s h e s , r a i s e s t h e q u e s t i o n o f p h y s i c a l f e a t u r e s o f t h e v e g e t a t i o n a s a c o n t r i b u t i n g f a c t o r t o t h e h a b i t a t s o f w r e n s a n d r e d w i n g s . P i e m a n ' s s t u d y m a r s h c o n t a i n e d a u n i f o r m s t a n d o f 117 c a t t a i l i n w h i c h b o t h w r e n s a n d r e d w i n g s n e s t e d i n t h e e a r l y p a r t o f t h e s e a s o n , c o m p l i m e n t e d by a g r o w t h o f s e d g e s ( p r i m a r i l y S c i r p u s sp* ) t h a t was s e a w a r d f r o m t h e c a t t a i l s t a n d a n d became a v a i l a b l e l a t e r i n t h e s e a s o n . O n l y w r e n s n e s t e d i n t h i s s e d g e v e g e t a t i o n . I n a d d i t i o n , y e l l o w h e a d s , n o r m a l l y a s s o c i a t e d w i t h f r e s h - w a t e r m a r s h e s ( B e n t 1 9 5 8 ) , w e r e a b s e n t f r o m h i s m a r s h . T h o u g h b o t h w r e n s a n d r e d w i n g s u s e d t h e same v e g e t a t i o n i n P i e m a n ' s m a r s h , t h e y were s p a t i a l l y s e g r e g a t e d , a n d w r e n s , when n e s t i n g n e a r r e d w i n g n e s t s , t e n d e d t o n e s t i n h i g h e r , d e n s e r v e g e t a t i o n t h a n r e d w i n g s . I f g r e a t e r v e g e t a t i o n h e i g h t a n d d e n s i t y a r e i m p o r t a n t f e a t u r e s o f e i t h e r f u n d a m e n t a l o r r e a l i z e d w r e n h a b i t a t ( M i l l e r 1 9 6 7 ) , i t c o u l d h e l p t o e x p l a i n my o b s e r v a t i o n s i n P i t t Meadows o f a p r e f e r e n c e b y w r e n s f o r S p i r a e a a s o p p o s e d t o t h e s e d g e v e g e t a t i o n p r e f e r r e d by r e d w i n g s . I w i l l d i s c u s s t h e i m p o r t a n c e o f p h y s i c a l f e a t u r e s o f t h e v e g e t a t i o n l a t e r i n t h i s d i s c u s s i o n i n t h e \" O t h e r F a c t o r s \" s e c t i o n . b . C o m p e t i t i o n I n t e r f e r e n c e c o m p e t i t i o n , a s d e f i n e d b y t w o s p e c i e s h a v i n g a n e g a t i v e e f f e c t o n e a c h o t h e r , a p p e a r s t o be a n u l t i m a t e f a c t o r s e l e c t i n g f o r h a b i t a t s e g r e g a t i o n b e t w e e n L o n g - b i l l e d M a r s h H r e n s a n d B e d - w i n g e d B l a c k b i r d s i n P i t t M e a d o w s . F o r more s o l i d e v i d e n c e , one s h o u l d u n d e r t a k e e x p e r i m e n t a l w o r k s u c h a s r e m o v a l o r a d d i t i o n o f one o f t h e s p e c i e s , w i t h a p p r o p r i a t e c o n t r o l s , a n d o b s e r v a t i o n o f a n y c h a n g e s i n n e s t i n g s u c c e s s . I d i d n o t do t h i s i n t h e p r e s e n t s t u d y , b u t e v i d e n c e f o r w r e n s h a v i n g a n e g a t i v e e f f e c t o n r e d w i n g s was a d d e d t o t h a t p r o v i d e d by o t h e r 118 i,. a u t h o r s ( f t l l e n 1 9 1 4 , B u r t 1 9 7 0 , P i e m a n 1 9 7 7 a ) . a d d i t i o n a l l y , I h a v e p r e s e n t e d e v i d e n c e f o r r e d w i n g s h a v i n g a n e g a t i v e e f f e c t o n w r e n s . A g g r e s s i v e n e s s by r e d w i n g s on w r e n s h a s b e e n o b s e r v e d i n o t h e r s t u d i e s , b u t t h e s e s t u d i e s h a v e p r o v i d e d no f u r t h e r s u p p o r t i v e e v i d e n c e f o r w r e n s b e i n g a f f e c t e d by r e d w i n g s . The a g r e e m e n t o f my r e s u l t s w i t h t h o s e o f o t h e r s s u p p o r t s t h e i d e a . t h a t , i n g e n e r a l , i n t e r s p e c i f i c c o m p e t i t i o n i s a n i m p o r t a n t f a c t o r i n f l u e n c i n g h a b i t a t s e l e c t i o n by w r e n s a n d r e d w i n g s . I n t e r s p e c i f i c c o m p e t i t i o n c a u s i n g s e g r e g a t i o n b e t w e e n w r e n s a n d r e d w i n g s c o u l d , i n c o m b i n a t i o n w i t h o t h e r f a c t o r s , i n f l u e n c e t h e s e s p e c i e s * n e s t i n g s t r a t e g i e s . T h e o r i e s o n how p o l y g y n y , o r t h e m a t i n g o f one m a l e w i t h more t h a n o n e f e m a l e , c o u l d h a v e e v o l v e d i n m a r s h w r e n s a n d r e d w i n g s h a v e f o c u s e d p r i m a r i l y on t h e i m p o r t a n c e o f p h y s i c a l f e a t u r e s i n t h e b i r d ' s h a b i t a t a n d how t h e s e c o u l d i n f l u e n c e t h e s e l e c t i o n f o r p o l y g y n y ( V e r n e r 1 9 6 4 ; O r i a n s 1 9 6 1 , 1 9 6 9 , a n d 1 9 7 0 ) . P i e m a n ( p e r s . comm.) h a s b e e n w o r k i n g o n t h e h y p o t h e s i s t h a t i n t e r s p e c i f i c c o m p e t i t i o n a l s o p l a y s a f u n d a m e n t a l r o l e i n t h e e v o l u t i o n o f p o l y g y n y i n w r e n s a n d r e d w i n g s * My r e s u l t s s a y n o t h i n g a b o u t t h e o c c u r r e n c e o f p o l y g y n y v e r s u s monogamy o r c o l o n i a l i t y o f m a r s h p a s s e r i n e s , b u t t h e y d o s u p p o r t t h e h y p o t h e s i s t h a t i n t e r s p e c i f i c c o m p e t i t i o n r e s t r i c t s t h e r a n g e o f w r e n a n d r e d w i n g h a b i t a t s , a n d c o u l d t h u s r e s u l t i n t h e c o n t a g i o u s n e s t i n g o f b o t h s p e c i e s . O t h e r f a c t o r s c o u l d c o m b i n e w i t h c o m p e t i t i o n t o s e l e c t f o r p o l y g y n y o v e r o t h e r s y s t e m s o f n e s t i n g . F o r e x a m p l e . P i e m a n ( p e r s . comm*) b e l i e v e s t h a t r e d w i n g p o l y g y n y e v o l v e d a s a c o m p r o m i s i n g s t r a t e g y b e t w e e n t h e n e e d f o r m u t u a l n e s t d e f e n s e a g a i n s t w r e n s , f a v o u r i n g c o l o n i a l i t y , a n d l i m i t e d f o o d 1 19 r e s o u r c e s , f a v o u r i n g t e r r i t o r i a l i t y . The f a c t t h a t t h e maximum 1977 d e n s i t i e s 1 o f a c t i v e n e s t s o f b o t h w r e n s and r e d w i n g s were l o w e r i n my m a r s h ( 2 . 6 n e s t s / h a f o r w r e n s , 1 . 8 n e s t s / h a f o r r e d w i n g s ) t h a n i n P i e m a n ' s m a r s h ( 7 . 0 n e s t s / h a f o r w r e n s , 3 . 6 n e s t s / h a f o r r e d w i n g s ) h a s a d i r e c t b e a r i n g o n t w o o f P i e m a n ' s ( p e r s . comm. ) h y p o t h e s e s . The f i r s t i s t h a t , a t l o w e r w r e n d e n s i t i e s , t h e i m p a c t o n w r e n s o f r e d w i n g s s h o u l d e x c e e d t h a t o f o t h e r w r e n s . T h o u g h t h e s i t u a t i o n s a r e n o t s t r i c t l y c o m p a r a b l e , s i n c e r e d w i n g s a l s o o c c u r r e d a t l o w e r d e n s i t i e s i n my m a r s h , t h i s was t h e c a s e i n my s t u d y . T h e s e c o n d h y p o t h e s i s i s b a s e d p r i m a r i l y o n P i e m a n ' s c o r r e l a t e d o b s e r v a t i o n s o f a g r e a t e r i m p a c t o f w r e n s on r e d w i n g s i n 1976 t h a n i n 1977 a n d a l o w e r w r e n d e n s i t y i n 1976 t h a n i n 1 9 7 7 . He p r e d i c t s t h a t w r e n s c o u l d h a v e a n i m p a c t on r e d w i n g s e v e n a t l o w w r e n d e n s i t i e s b e c a u s e t h e d e c r e a s e i n i n t r a s p e c i f i c s t r i f e a s s o c i a t e d w i t h t h e s e l o w d e n s i t i e s w o u l d l e a v e more t i m e f o r w r e n s t o i n t e r f e r e w i t h c o m p e t i n g r e d w i n g s . T h e f a c t t h a t I o b s e r v e d t h i s w r e n - r e d w i n g i m p a c t a t t h e l o w w r e n d e n s i t i e s i n my m a r s h s u p p o r t s t h i s h y p o t h e s i s . A p o s s i b l e a l t e r n a t i v e e x p l a n a t i o n o f t h e i m p a c t o f w r e n s on r e d w i n g s c o u l d , h o w e v e r , be f o u n d i n t h e f a c t t h a t r e d w i n g d e n s i t i e s w e r e a l s o l o w e r i n my m a r s h t h a n i n P i e m a n ' s . I f r e d w i n g s h a v e some f o r m o f m u t u a l n e s t d e f e n s e , l o w e r r e d w i n g d e n s i t i e s c o u l d r e d u c e t h e e f f e c t i v e n e s s o f t h i s d e f e n s e ( p r i m a r i l y r e d w i n g - w r e n c h a s e s ) , a n d i n c r e a s e t h e d e t r i m e n t a l i m p a c t o f w r e n s o v e r t h a t f o u n d i n * n u m b e r o f s i m u l t a n e o u s l y a c t i v e n e s t s p e r t o t a l a r e a o f m a l e t e r r i t o r i e s . 120 s i t u a t i o n s with higher redwing densities. 3. Factors Other Than I n t e r s p e c i f i c Competition There are undoubtedly other forces a f f e c t i n g wren-redwing segregation besides competition with each other* The nesting success of both species varied with vegetation type (Table VII). Although these differences were not s i g n i f i c a n t s t a t i s t i c a l l y (p > -05), I believe that vegetation e f f e c t s are important. In the extreme, i f the only concern to a nesting wren were that she avoid redwings, she should be more successful i n any s u i t a b l e habitat devoid of redwings. There was i n fact one study plot (Plot C) i n the present study the edge of which was located 300 m from the nearest redwing t e r r i t o r y . Brens i n three of the other plots with redwings were more successful on the average than those i n t h i s plot, so other influences must be considered. Thus f a r , I have discussed the \"ultimate\" f a c t o r s influencing habitat s e l e c t i o n as opposed to \"proximate\" f a c t o r s . The d i s t i n c t i o n between the two types of factors i s stated by Hilden (1965) as follows: \"In habitat s e l e c t i o n , the former (ultimate)* are e s s e n t i a l for the survival:of the species, and constitute the underlying reasons determining why each species breeds i n i t s s p e c i f i c environment. The l a t t e r (proximate), on the other hand, only serve to release the s e t t l i n g reaction and need not necessarily have any b i o l o g i c a l significance to the species as such.\" In spite of t h i s d i s t i n c t i o n , proximate factors can often suggest the ultimate factor behind the habitat selection (Hilden 1 My terms in parentheses. 121 1 9 6 5 , V e r n e r 1 9 7 5 b ) . F o r e x a m p l e , i f i n t e r s p e c i f i c c o m p e t i t i o n i s t h e m o s t i m p o r t a n t u l t i m a t e f a c t o r i n f l u e n c i n g h a b i t a t s e l e c t i o n i n w r e n s a n d r e d w i n g s , t h e p r e s e n c e o f t h e o t h e r s p e c i e s w o u l d l i k e l y s e r v e a s t h e a v o i d a n c e c u e , o r p r o x i m a t e f a c t o r . Some o f my r e s u l t s s u g g e s t t h e b i r d s c u e o n f a c t o r s o t h e r t h a n t h e p r e s e n c e o r a b s e n c e o f t h e o t h e r s p e c i e s . F i r s t , w r e n s a r e mos t a b u n d a n t b y f a r i n t h e S p i r a e a s h r u b h a b i t a t i n e a r l y w i n t e r ( F i g . 11) when r e d w i n g s a r e n e a r l y a b s e n t f r o m t h e m a r s h . I f t h e g r e a t e r a b u n d a n c e o f w r e n s i n S p i r a e a h a b i t a t i s c a u s e d e x c l u s i v e l y b y t h e a v o i d a n c e o f r e d w i n g s , t h e y s h o u l d u t i l i z e o t h e r h a b i t a t s i n t h e a b s e n c e o f r e d w i n g s . S e c o n d , i f S p i r a e a i s o n l y i m p o r t a n t t o w r e n s i n w i n t e r , i n s p r i n g t h e y m i g h t a t t e m p t t o u s e a n d s u b s e q u e n t l y be e x p e l l e d b y r e d w i n g s f r o m t h e b u l r u s h s p e c i e s o f t h e c e n t r a l m a r s h . B a s e d on c e n s u s r e s u l t s ( F i g . 12) a n d l o c a t i o n s o f s p r i n g w r e n t e r r i t o r i e s i n n e s t s t u d y p l o t s , t h i s d i d n o t o c c u r . 1 S r e n s s i m p l y i n c r e a s e d i n a b u n d a n c e i n t h e S p i r a e a . T h e r e i s a t h i r d r e s u l t t h a t p u t s i n j e o p a r d y t h e h y p o t h e s i s t h a t w r e n s c h o o s e h a b i t a t p r i m a r i l y i n r e s p o n s e t o t h e a b s e n c e o f r e d w i n g s . An o b v i o u s p h y s i c a l f a c t o r t h a t a c c o m p a n i e d w r e n movement i n t o T y p h a l a t i f o l i a a n d S c i r p u s s p p . i n t h e s u m m e r , i n a d d i t i o n t o d e c r e a s i n g r e d w i n g a b u n d a n c e , was a n i n c r e a s e i n t h e h e i g h t o f t h e n e s t s u b s t r a t e v e g e t a t i o n o v e r t h e h e i g h t i n t h e s p r i n g n e s t i n g s e a s o n (p < . 0 0 5 f o r b o t h T . l a t i f o l i a a n d S . a c u t u s . S t u d e n t ' s t ) . W h a t , t h e n , a r e some f e a t u r e s o f t h e 1 T h e r e was e v i d e n c e , h o w e v e r , s u g g e s t i n g t h a t one m a l e w r e n e s t a b l i s h e d a n e a r l y t e r r i t o r y i n T . l a t i f o l i a a n d was f o r c e d t o a b a n d o n t h e t e r r i t o r y b e c a u s e o f r e d w i n g p r e s e n c e . 122 h a b i t a t t h a t m i g h t e x p l a i n t h e a b o v e r e s u l t s a n d o f f e r a l t e r n a t i v e s o r c o m p l e m e n t s t o i n t e r s p e c i f i c c o m p e t i t i o n a s u l t i m a t e c a u s e s o f s e g r e g a t i o n ? G o o d s o n g b i r d h a b i t a t mus t p r o v i d e r e l i a b l e n e s t s u p p o r t . T h i s i s p a r t i c u l a r l y c r u c i a l i n m a r s h v e g e t a t i o n , w h i c h i s o f t e n s t r u c t u r a l l y w e a k . B e c a u s e o f w i d e l y f l u c t u a t i n g w a t e r l e v e l s i n many m a r s h e s , i t w o u l d a l s o be t o a b i r d ' s a d v a n t a g e t o n e s t s u f f i c i e n t l y h i g h i n t h e v e g e t a t i o n t o a v o i d f l o o d i n g . When c o n s i d e r i n g n e s t s u p p o r t , t h e c o m b i n e d w e i g h t o f t h e n e s t a n d t h e b i r d i s i m p o r t a n t . W r e n s w e i g h a b o u t o n e - f o u r t h a s much a s r e d w i n g s , a n d t h e n e s t s o f t h e t w o s p e c i e s w e i g h a p p r o x i m a t e l y t h e s a m e . 1 T h u s , w r e n s c a n a f f o r d t o n e s t h i g h e r a n d d o , i n f a c t , do s o i n a l l t h e d i f f e r e n t v e g e t a t i o n t y p e s o f t h e p r e s e n t s t u d y m a r s h . W i t h t h e e x c e p t i o n o f T y p h a s p p . , t y p i c a l m a r s h v e g e t a t i o n , w h i c h i s p r i m a r i l y s e d g e s , i s n o t r o b u s t a n d p r o b a b l y o f f e r s p o o r s u p p o r t f o r p a s s e r i n e n e s t s ( V e r n e r 1 9 6 5 , V e r n e r a n d E n g e l s e n 1 9 7 0 , F o w l e 1 9 4 2 , H o l m 1 9 7 3 ) , p a r t i c u l a r l y f o r t h o s e n e s t s p l a c e d h i g h i n t h e v e g e t a t i o n l i k e t h o s e o f w r e n s . S h r u b s , l i k e S p i r a e a d o u g l a s i i , a r e r o b u s t a n d , a s i s t h e c a s e w i t h S p i r a e a , o f t e n s t a n d t a l l e r t h a n s e d g e s a n d o t h e r e m e r g e n t s . T h u s , when w r e n s move i n t o T . l a t i f o l i a a n d S c i r p u s s p p , i n summer t h e y may i n d e e d b e r e s p o n d i n g t o a n i n c r e a s e i n v e g e t a t i o n h e i g h t . T h i s i s f u r t h e r s u p p o r t e d b y t h e f a c t t h a t t h e f o u r w r e n b r e e d i n g n e s t s p l a c e d i n t h e p r e v i o u s y e a r ' s * N e s t s i n t h e f i e l d a p p e a r t o b e made o f t h e same a m o u n t s o f m a t e r i a l , a n d I t o o k t h e d r y w e i g h t s o f t w o s a m p l e n e s t s . The w r e n n e s t w e i g h e d 7 3 . 2 g , c o m p a r e d t o 7 0 . 3 g f o r t h e r e d w i n g n e s t . 123 g r o w t h o f S . a c u t u s i n t h e s p r i n g w e r e i n t a l l e r p l a n t s o f t h i s s p e c i e s t h a n t h o s e i n w h i c h r e d w i n g s w e r e n e s t i n g d u r i n g t h e same p e r i o d (p < . 0 3 , S t u d e n t ' s t ) . The h e a v i e r r e d w i n g , when u s i n g s e d g e v e g e t a t i o n , mus t n e s t c l o s e r t o t h e w a t e r t h a n w r e n s t o o b t a i n a d e q u a t e n e s t s u p p o r t * at t h e s e l o w e r l e v e l s S c i r p u s s t e m s a n d l e a v e s a r e c l o s e t o g e t h e r , a n d r e d w i n g s h a v e a m p l e s u r f a c e f o r n e s t a t t a c h m e n t s . S i n c e S c i r p u s i s s h o r t e r t h a n t h e S p i r a e a p r e f e r r e d by w r e n s , v e g e t a t i o n h e i g h t may be a c u e u s e d b y b o t h s p e c i e s , a n d t h e u l t i m a t e r e a s o n s f o r s e l e c t i n g d i f f e r e n t h e i g h t s o f v e g e t a t i o n c o u l d be n e s t s u p p o r t and a v o i d a n c e o f f l o o d i n g . P r o t e c t i o n f r o m p r e d a t o r s a n d t h e w e a t h e r c o u l d i n f l u e n c e t h e s e l e c t i o n o f h a b i t a t by t h e two s p e c i e s . P i e m a n o b s e r v e d w r e n s n e s t i n g i n h i g h e r , more d e n s e v e g e t a t i o n t h a n r e d w i n g s o n l y i n s i t u a t i o n s i n w h i c h t h e two s p e c i e s n e s t e d n e a r t o o n e a n o t h e r , s u g g e s t i n g t h a t t h e s e v e g e t a t i o n f e a t u r e s a r e o n l y i m p o r t a n t t o w r e n s f o r p r o t e c t i o n f r o m r e d w i n g s . I n s p i t e o f t h i s r e s u l t , h i g h d e n s i t y a n d h e i g h t o f v e g e t a t i o n c o u l d p r o t e c t w r e n s a n d t h e i r n e s t s f r o m w e a t h e r a n d b o t h l a n d a n d a v i a n p r e d a t o r s . S p i r a e a d o u q l a s i i h a s b o t h t h e s e p r o p e r t i e s , a n d w r e n s s e l d o m u s e a n y o t h e r h a b i t a t i n t h e w i n t e r , s u g g e s t i n g t h e i m p o r t a n c e o f t h i s h a b i t a t t o p r o t e c t i o n f r o m t h e e l e m e n t s . B e d w i n g s a r e more p r o n e t o c h a s i n g p r e d a t o r s , p a r t i c u l a r l y o t h e r b i r d s , t h a n w r e n s , a n d v e g e t a t i o n t h a t i s s h o r t e r a n d l e s s d e n s e a t t h e u p p e r v e g e t a t i o n l e v e l s may be more s u i t a b l e t o t h e m . S c i r p u s s p p . h a v e t h e s e p r o p e r t i e s a n d y e t c a n h i d e n e s t s f r o m t h e v i e w o f l a n d p r e d a t o r s t h a t r e l y o n s i g h t f o r d e t e c t i o n o f n e s t s . We saw e a r l i e r t h a t l a t e r a l v i s i b i l i t y o f r e d w i n g n e s t s 124 was l e s s t h a n t h a t o f w r e n n e s t s ( T a b l e I I I ) . The a s s o c i a t i o n o f r e d w i n g s w i t h d e e p e r w a t e r a n d o p e n w a t e r n e a r t o n e s t s may b e t h e k e y f e a t u r e t h a t a t t r a c t s r e d w i n g s t o c e n t r a l m a r s h h a b i t a t s . T h i s a t t r a c t i o n may r e f l e c t t h e p r o t e c t i o n f r o m m a m m a l i a n p r e d a t o r s t h a t w a t e r a f f o r d s r e d w i n g s . L o w e r w a t e r l e v e l s a n d f e w e r o p e n w a t e r p a t c h e s i n . S p i r a e a h a b i t a t i n t h e m a r s h may a l s o h e l p e x p l a i n t h e a b s e n c e o f r e d w i n g s f r o m t h i s h a b i t a t , e v e n t h o u g h r e d w i n g s f r e q u e n t l y n e s t i n t r e e s a n d s h r u b s i n o t h e r a r e a s . I n f a c t , r e d w i n g n e s t s h a v e b e e n r e c o r d e d i n S p i r a e a , p r i m a r i l y g r o w i n g on d y k e s b e s i d e s l o u g h s a n d d i t c h e s , i n P i t t Meadows i n p r e v i o u s y e a r s ( B . C . P r o v i n c i a l Museum n e s t r e c o r d s c h e m e ) . 4 . F a c t o r s O p p o s i n g S e g r e g a t i o n L i m i t s t o t h e d e g r e e o f s e g r e g a t i o n b e t w e e n w r e n s a n d r e d w i n g s mus t e x i s t . H a t e r l e v e l s a r e p r o b a b l y i m p o r t a n t i n t h i s r e g a r d . I f r e d w i n g s move t o o f a r i n t o d e e p e r w a t e r , t h e y a r e f o r c e d t o a t t e m p t t o a t t a c h t h e i r n e s t s t o t h e t h i n , f l i m s y s t e m s t h a t a r e c h a r a c t e r i s t i c o f h i g h e r p o r t i o n s o f s e d g e s . S i m i l a r l y , i f w r e n s move t o o f a r away f r o m w a t e r t o t h e e x t r e m e o f n e s t i n g e x c l u s i v e l y on d r y l a n d , t h e y n o l o n g e r h a v e t h e p r o t e c t i o n f r o m p r e d a t o r s t h a t w a t e r p r o b a b l y a f f o r d s t h e m , a n d \"i t h e y r e m o v e t h e m s e l v e s f r o m a f o o d s o u r c e ( a q u a t i c i n v e r t e b r a t e s ) t h a t i s n o r m a l l y i m p o r t a n t i n t h e i r d i e t ( W e l t e r 1 9 3 5 , V e r n e r a n d E n g e l s o n 1 9 7 0 ) . 125 A n o t h e r p o s s i b l e f o r c e o p p o s i n g w r e n - r e d w i n g s e g r e g a t i o n i s t h e i n t r a s p e c i f i c i n t e r f e r e n c e ( n e s t d e s t r u c t i o n ) p r o b a b l y e x p e r i e n c e d b y w r e n s ( P i e m a n 1 9 7 7 b ) . T h i s w o u l d t e n d t o s e l e c t f o r w r e n s t h a t w o u l d n e s t f u r t h e r f r o m o t h e r w r e n s a n d c l o s e r t o r e d w i n g s , p a r t i c u l a r l y i f w r e n d e n s i t y i s h i g h . T h i s w r e n - w r e n i n t e r f e r e n c e was n o t a n i m p o r t a n t f a c t o r f o r t h e w r e n p o p u l a t i o n s t u d i e d h e r e , e v e n when w r e n s n e s t e d c l o s e t o o r w i t h i n r e d w i n g t e r r i t o r i e s , w h e r e t h e y m i g h t be e x p e c t e d t o n e g l e c t n e s t s b e c a u s e o f r e d w i n g h a r a s s m e n t . S i n c e w r e n d e n s i t i e s i n t h i s m a r s h w e r e t h e l o w e s t y e t r e p o r t e d ( W e l t e r 1 9 3 5 , V e r n e r 1 9 6 5 a , P i e m a n p e r s . c o m m . ) , t h i s i n t e r f e r e n c e may s t i l l be i m p o r t a n t f o r d e n s e r p o p u l a t i o n s . A s i l l u s t r a t e d by a p r e v i o u s d i s c u s s i o n o f t h e e f f e c t s o f y e l l o w h e a d s , c o m p e t i t i o n w i t h o t h e r s p e c i e s c o u l d o p p o s e s e g r e g a t i o n o f w r e n s f r o m r e d w i n g s . The Common Y e l l o w t h r o a t may a f f e c t o b s e r v e d w r e n h a b i t a t . I h a v e a l r e a d y d e m o n s t r a t e d t h a t w r e n s a n d y e l l o w t h r o a t s s h a r e t h e same \" D e n s e S p i r a e a \" h a b i t a t w i t h some s u g g e s t i o n o f b o t h s p a t i a l a n d t e m p o r a l s e g r e g a t i o n w i t h i n t h a t h a b i t a t . I a l s o o b s e r v e d a m a l e w r e n c h a s i n g a m a l e y e l l o w t h r o a t . Y e l l o w t h r o a t s , a member o f t h e Wood W a r b l e r ( P a r u l i d a e ) f a m i l y , a r e l i k e l y b e t t e r a d a p t e d t h a n w r e n s t o t h e s l i g h t l y d r i e r c o n d i t i o n s i n w h i c h t h e y a r e f o u n d , a n d , t o t h e e x t e n t t h a t t h e y c o m p e t e w i t h w r e n s f o r f o o d a n d / o r s p a c e , t h e y may make i t a d v a n t a g e o u s f o r w r e n s t o r e f r a i n f r o m n e s t i n g t o o f a r away f r o m damp a r e a s . 126 5- C l o s i n g S t a t e m e n t I n t h e p r e c e d i n g d i s c u s s i o n I h a v e t r i e d t o p o i n t o u t t h a t , t h o u g h I p r o v i d e e v i d e n c e w h i c h s u p p o r t s t h e h y p o t h e s i s t h a t c o m p e t i t i o n i s a n i m p o r t a n t u l t i m a t e c a u s e o f w r e n - r e d w i n g s e g r e g a t i o n , o t h e r f a c t o r s , i n d e p e n d e n t o f i n t e r s p e c i f i c i n t e r a c t i o n s , mus t n o t be i g n o r e d . The o b s e r v e d d i f f e r e n c e s b e t w e e n t h e h a b i t a t s o f t h e t w o s p e c i e s a n d t h e l a c k o f e x p e r i m e n t a l work in t h e p r e s e n t s t u d y t o d e t e r m i n e t h e u l t i m a t e f a c t o r s o f h a b i t a t s e l e c t i o n , s u g g e s t t h a t p h y s i c a l f a c t o r s o f t h e h a b i t a t s r e q u i r e f u r t h e r i n v e s t i g a t i o n . B o t h i n t e r s p e c i f i c a n d i n t r a s p e c i f i c c o m p e t i t i o n p r o b a b l y c o m b i n e w i t h o t h e r f a c t o r s t o i n f l u e n c e h a b i t a t s e l e c t i o n , a n d t h e r e l a t i v e i m p o r t a n c e o f e a c h o f t h e f a c t o r s d i f f e r s w i t h d i f f e r e n t m a r s h s i t u a t i o n s . 127 Management I m p l i c a t i o n s M a n a g e m e n t i m p l i c a t i o n s w i l l be d i s c u s s e d w i t h t h e o b j e c t i v e i n mind o f a v o i d i n g a n y d r a s t i c r e d u c t i o n s i n p o p u l a t i o n s i z e o f a n y o f t h e m a r s h p a s s e r i n e s p e c i e s - The m a r s h p a s s e r i n e c o m m u n i t y i s o n l y o n e c o m p o n e n t i n a c o m p l e x w e t l a n d s y s t e m , l o c a t e d i n a n a r e a w h i c h i s t o b e managed f o r m u l t i p l e - u s e , a n d o v e r a l l s p e c i e s d i v e r s i t y s h o u l d be a n i m p o r t a n t c o n s i d e r a t i o n . F o r t h i s r e a s o n , a n y p o l i c i e s t h a t I r e c o m m e n d w o u l d be u n d e r t a k e n o n l y i f no s e r i o u s c o n f l i c t e x i s t s b e t w e e n them a n d e i t h e r t h e management p l a n s o r t h e w e l f a r e o f o t h e r marsh s p e c i e s . N a t u r e s t u d y i s p r o b a b l y t h e m o s t i m p o r t a n t r e c r e a t i o n a l u s e made o f mar sh p a s s e r i n e s . F o r s c i e n t i f i c s t u d y , I b e l i e v e t h e p a s s e r i n e c o m m u n i t y a n d t h e u n i q u e c h a r a c t e r i s t i c s o f t h i s p a r t i c u l a r m a r s h , n o t t h e l e a s t o f w h i c h i s an a b i l i t y t o c o n t r o l w a t e r l e v e l s , a r e i m p o r t a n t . H o w e v e r , t h i s i m p o r t a n c e i s l i m i t e d by t h e e x t e n t t o w h i c h t h e a r e a w i l l b e u s e d f o r r e c r e a t i o n a l p u r p o s e s * H e c o m m e n d a t i o n s b a s e d on a n o v e r a l l w i l d l i f e i n v e n t o r y o f t h e a r e a h a v e b e e n g i v e n p r e v i o u s l y ( H u n y a n 1978) . I b a s e my r e c o m m e n d a t i o n s o n t h e o b s e r v e d h a b i t a t s t h a t t h e s p e c i e s o c c u p y . T h e u l t i m a t e c a u s e o f t h i s h a b i t a t s e l e c t i o n , w h e t h e r i t be c o m p e t i t i o n o r p h y s i c a l h a b i t a t r e q u i r e m e n t s , i s n o t known w i t h e n o u g h c e r t a i n t y t o u t i l i z e i n a s s e s s i n g management p o l i c i e s * I t may, i n a n y c a s e , b e u n n e c e s s a r y . F r o m t h e s e o b s e r v e d h a b i t a t s , t h e d i v e r s i t y o f m a r s h v e g e t a t i o n t h a t e x i s t s i n t h e PWMA seems i m p o r t a n t t o m a r s h p a s s e r i n e s . 128 O f t h e f o u r p a s s e r i n e s p e c i e s , y e l l o w t h r o a t s a n d w r e n s w o u l d l i k e l y b e t h e mos t s e n s i t i v e t o v e g e t a t i o n c h a n g e s , p a r t i c u l a r l y s i n c e management e f f o r t s w i l l p r o b a b l y r e d u c e t h e q u a n t i t y o f t h e s h r u b S p i r a e a d o u q l a s i i . Y e l l o w t h r o a t s a r e m o s t c o m m o n l y s e e n i n t h e P i t t Meadows r e g i o n o f a l l t h e p o p u l a r a r e a s f o r b i r d s t u d y i n t h e V a n c o u v e r B i r d C h e c k l i s t a r e a ( C a m p b e l l 1974) a n d , t h o u g h i t may b e o b s e r v e d i n s m a l l n u m b e r s i n a f e w a r e a s o f C o q u i t l a m a n d S u r r e y , t h e PWHA o f f e r s t h e m o s t a c c e s s i b l e y e l l o w t h r o a t h a b i t a t ( M . S c h o u t e n , p e r s . c o m m . ) . a f e w s i n g i n g m a l e s u s e t h e g r a s s y d y k e s i n t h e P i t t P o l d e r , b u t a r e o t h e r w i s e r e s t r i c t e d t o t h e S p i r a e a d o u g l a s i i - C a l a m a q r g s t i s c a n a d e n s i s a s s o c i a t i o n . P r e s e r v a t i o n o f some a r e a s o f t h i s h a b i t a t h a s t h u s p r e v i o u s l y b e e n r e c o m m e n d e d . S p i r a e a i s a l s o u s e d e x t e n s i v e l y by w r e n s , t h o u g h t h e y a r e s i m i l a r l y a b u n d a n t i n T y p h a . E n c o u r a g e m e n t , i f p o s s i b l e , o f T . l a t i f o l i a w o u l d l i k e l y o f f s e t a n y l o s s e s e x p e r i e n c e d by w r e n s due t o e x t e n s i v e r e m o v a l o f S p i r a e a . S o n g S p a r r o w s a n d B e d - w i n g e d B l a c k b i r d s w o u l d , i n my o p i n i o n , b e l e s s s e n s i t i v e t o v e g e t a t i o n c h a n g e s . I n a d d i t i o n t o t h e \" D e n s e S p i r a e a \" h a b i t a t . S o n g S p a r r o w s make u s e o f t h e n u m e r o u s \" s h r u b b y \" d y k e s i n t h e PWMA. B e d w i n g s i n h a b i t more o p e n m a r s h a r e a s w i t h s t a n d i n g w a t e r , t h e h a b i t a t s f o r w h i c h c u r r e n t management i s a i m e d . The o n l y s i t u a t i o n i n w h i c h t h e r e d w i n g p o p u l a t i o n m i g h t s u f f e r w o u l d b e one i n w h i c h o n l y S . a c u t u s was a v a i l a b l e a s n e s t i n g s u b s t r a t e , a n d w a t e r l e v e l s w e r e k e p t h i g h . T h i s w o u l d f o r c e r e d w i n g s t o n e s t h i g h e r w h e r e , p a r t i c u l a r l y i n jS. a c u t u s , n e s t s u p p o r t i s i n f e r i o r t o t h a t a t l o w e r l e v e l s o f t h e m a r s h v e g e t a t i o n w h e r e r e d w i n g s n o r m a l l y 129 n e s t . An a d d i t i o n a l o p t i o n i s s t i l l a v a i l a b l e t o r e d w i n g s i n e v e n t h i s e x t r e m e s i t u a t i o n , s i n c e t r e e s e x i s t n e a r b y , a n d r e d w i n g s o f t e n n e s t i n t r e e s i n o t h e r l o c a t i o n s ( B e n t 1 9 5 8 , C a s e a n d H e w i t t 1963) a n d h a v e b e e n o b s e r v e d n e s t i n g i n t r e e s i n r e s p o n s e t o f l o o d i n g o f s e d g e n e s t i n g a r e a s i n I o w a ( B u r t 1 9 7 0 ) . Some e n h a n c e m e n t o f p a s s e r i n e p o p u l a t i o n s may r e s u l t f r o m c u r r e n t management p l a n s t o s t a b i l i z e w a t e r l e v e l s a n d a p o s s i b l e f u t u r e f e r t i l i z a t i o n o f PWHA w a t e r . Many o f t h e r e d w i n g n e s t s p l a c e d i n S . a c u t u s w e r e f l o o d e d i n J u n e by w a t e r l e v e l s s u d d e n l y r i s i n g t o 1.3 m a b o v e s e a l e v e l ( a n a v e r a g e w a t e r d e p t h a t f l o o d e d n e s t s i t e s i n S-_ a c u t u s o f 30 c m ) . T h u s , s t a b i l i z i n g w a t e r l e v e l s a t a m o d e r a t e l e v e l i n t h e m a r s h c o u l d b e n e f i t r e d w i n g s . A s m a l l c o l o n y o f Y e l l o w - h e a d e d B l a c k b i r d s t h a t a p p e a r t o u t i l i z e t h e PWMA f o r n e s t i n g e a c h y e a r c o u l d a l s o b e n e f i t s T h i s y e l l o w h e a d c o l o n y i s e l u s i v e d u r i n g n e s t i n g , b u t t h e r e i s some e v i d e n c e t h a t i t n e s t e d i n S . a c u t u s i n 1977 ( R u n y a n 1978) a n d i n p r e v i o u s y e a r s ( R . R o b i n s o n , p e r s . c o m m . ) . T h e \" c e n t r a l m a r s h \" l o c a t i o n w o u l d be c o n s i s t e n t w i t h y e l l o w h e a d h a b i t a t r e p o r t e d i n o t h e r s t u d i e s . The w i d e l y f l u c t u a t i n g w a t e r l e v e l s o f t h e c e n t r a l m a r s h may be s e v e r e l y l i m i t i n g t h e n e s t i n g s u c c e s s o f t h i s s p e c i e s , a s n e s t s l i k e l y s u c c u m b t o t h e same f l o o d i n g e x p e r i e n c e d by r e d w i n g n e s t s i n S . a c u t u s . I f f e r t i l i z a t i o n o f t h e w a t e r , by a l l o w i n g a g r i c u l t u r a l r u n - o f f t o e n t e r t h e P U M A , i s e v e r a t t e m p t e d i t c o u l d i n c r e a s e a g u a t i c i n v e r t e b r a t e p o p u l a t i o n s . T h i s c o u l d o b v i o u s l y e n h a n c e m a r s h p a s s e r i n e p o p u l a t i o n s . 130 From t h e a b o v e d i s c u s s i o n , I r ecommend t h a t some e x t e n s i v e a r e a s o f S p i r a e a be c o n s e r v e d a n d t h a t T . l a t i f o l i a , i f p o s s i b l e , be e n c o u r a g e d . T h i s w o u l d h e l p t o r e t a i n d i v e r s i t y o f m a r s h p a s s e r i n e s a n d , t o t h e b e s t o f my k n o w l e d g e , w o u l d n o t c o n f l i c t w i t h o t h e r management p l a n s . 131 L ITERATURE C ITED A l l e n , A . A . 1 9 1 4 . The r e d - w i n g e d b l a c k b i r d ; a s t u d y i n t h e e c o l o g y o f a c a t t a i l m a r s h . L i n n a e a n S o c . N . Y . , P r o c . N o s . 2 4 - 2 5: 4 3 - 1 2 8 . B a r n a r d , A . E . 1 975 . 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A P P E N D I X fiesults of Harsh Census Transects 136 FALL AND WINTER MARSH CENSUS RESULTS,\"DENSE SPIRAEA\" Fall Early Winter Late Winter Long-billed Marsh Wren 5.8 ^ ± 1.52 km 7.1 ± 1.10 4.4 ± 0.96 Red-winged Blackbird 0.3* ± 0.26** 0.3 ± 0.35 0.5 ± 0.48 Song Sparrow 2.3 ± 0.66 1.0 ± 0.34 0.6 ± 0.36 Common Yellowthroat 4.3 ± 1 . 8 5 0.0 0.0 * Represents mean of total detections for all transects during respective period ** Standard error of mean, N = 12 137 SPRING AND SUMMER MARSH CENSUS RESULTS, \"DENSE SPIRAEA\" Early Spring Late Spring Summer Long-billed Marsh Wren 15. .1 males km - ± 3.07 18. .1 + 3. .63 11. .8 + 2. .72 Red-winged Blackbird 0. ,6* ± 0. 4 4 * * 1. .1 + 0. .57 0, .8 + 0, .42 Song Sparrow 0. .9 + 0. 33 1 , .2 + 0. .33 1 , .2 + 0, .44 Common Yellowthroat 0. .2 + 0. 16 5, .5 + 1, .40 10. .1 + 1 .16 * Represents mean of singing males for all transects during respective period ** Standard error of mean, N = 12 138 FALL AND WINTER MARSH CENSUS RESULTS, \"SEDGE-SPIRAEA' Common Yellowthroat Fall Early Winter Late Winter Long-billed & 3 birds ± 2 3 0 * 2 * ± 1 > 3 7 } Q Q ± , Q 5 Marsh Wren km J i d ' l \" i \" 9 S d ° - 5 ± ° - 3 6 ° - 3 ± ° - 2 3 4 - 7 ± 2 - 0 1 Blackbird Song SDarrow 1.1 ± 0.80 0.0 0 . 7 ± 0 . 6 9 0.0 0.0 0.0 * Standard error of mean, N = 8 139 SPRING AND SUMMER MARSH CENSUS RESULTS, \"SEDGE-SPIRAEA' Early Spring Late Spring Summer Long-billed n . 3 ma]es ± 2 . 3 1 * 1 2 . 8 ±1 .40 1 3 . 5 ± - 2 . 8 8 Marsh Wren km Red-winged Blackbird 5.0 ± 2.44 7.8 ± 2.95 3.8 ± 2.14 Song Sparrow 0.0 0.0 0.0 Common Yellowthroat 0.0 0.5 ± 0.25 3.3 ± 1.00 * Standard error of mean, N = 8 140 FALL AND WINTER MARSH CENSUS RESULTS, \"SCIRPUS ACUTUS' Common Yellowthroat Fall Early Winter Late Winter Long-billed 4 > 4 birds ] g o.3 ± 0.22 0.0 Marsh Wren km Red-winged ? 3 5 6 8 Blackbird Song Sparrow 0.0 0.0 0.0 0.9 ± 0.77 0.0 0.0 * Standard error of mean, N = 8 141 SPRING AND SUMMER MARSH CENSUS RESULTS, \"SCIRPUS ACUTUS\" Red-winged Blackbird Common Yellowthroat Early Spring Late Spring Summer Long-billed males n.63* 4 . 7 ± 1.63 14 .8 ± 3.11 Marsh Wren km 7.3 ± 1.35 8.5 ± 1.48 6.4 ± 1.54 Song Sparrow 0.0 0.0 0.0 0.0 0.0 0.0 * Standard error of mean, N = 8 142 FALL AND WINTER MARSH CENSUS RESULTS, \"SCIRPUS CYPERINUS\" Fall Early Winter Late Winter Long-bi1 led Marsh Wren 3J birds ± 1 > 7 0 * 0.5 ± 0.52 0.0 Red-winged Blackbird 0.0 0.0 4.1 ± 1.99 Song Sparrow 0.6 ± 0.62 0.0 0.0 Common Yellowthroat 0.0 0.0 0.0 * Standard error of mean, N = 8 SPRING AND SUMMER MARSH CENSUS RESULTS, \"SCIRPUS CYPERINUS Red-winged Blackbi rd Early Spring Late Spring Summer Long-billed 0 > 0 males ± ± Marsh Wren km 1.0 ± 1.03* 5.5 ± 3.04 1.8 ± 1 .27 Song Sparrow 0.0 0.0 0.0 5 ; ° ™ ™ t o-o 0.0 0.0 Yellowthroat * Standard error of mean, N = 8 "@en ; edm:hasType "Thesis/Dissertation"@en ; edm:isShownAt "10.14288/1.0094587"@en ; dcterms:language "eng"@en ; ns0:degreeDiscipline "Zoology"@en ; edm:provider "Vancouver : University of British Columbia Library"@en ; dcterms:publisher "University of British Columbia"@en ; dcterms:rights "For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use."@en ; ns0:scholarLevel "Graduate"@en ; dcterms:title "Comparative habitats of, and competition between, the long-billed marsh wren and the red-winged blackbird at Pitt Meadows, British Columbia"@en ; dcterms:type "Text"@en ; ns0:identifierURI "http://hdl.handle.net/2429/21456"@en .