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Total body water turnover and partitioning of salt excretion in glaucous-winged gulls, larus glaucescens Walter, Anne 1977

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TOTAL BODY WATER TURNOVER AND PARTITIONING OF SALT EXCRETION IN GLAUCOUS-WINGED GULLS, LARUS GLAUCESCENS by ANNE WALTER B.A. G r i n n e l l C o l l e g e , 1973 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE i n the Department of ZOOLOGY We accept t h i s t h e s i s as conforming to the r e q u i r e d standard THE UNIVERSITY OF BRITISH COLUMBIA March, 19 77 0 Anne Walter, 1977 In p r e s e n t i n g t h i s t h e s i s i n p a r t i a l f u l f i l m e n t o f the r e q u i r e m e n t s f o r an advanced degree at the U n i v e r s i t y o f B r i t i s h C olumbia, I agree t h a t the L i b r a r y s h a l l make i t f r e e l y a v a i l a b l e f o r r e f e r e n c e and stud y . I f u r t h e r agree t h a t p e r m i s s i o n f o r e x t e n s i v e c o p y i n g o f t h i s t h e s i s f o r s c h o l a r l y purposes may be g r a n t e d by the Head o f my Department o r by h i s r e p r e s e n t a t i v e s . I t i s u n d e r s t o o d t h a t c o p y i n g o r p u b l i c a t i o n o f t h i s t h e s i s f o r f i n a n c i a l g a i n s h a l l not be a l l o w e d w i t h o u t my w r i t t e n p e r m i s s i o n . Department o f ~z.Do\t>c^ The U n i v e r s i t y o f B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 ABSTRACT 1. Two aspects of long-term s a l t and water e x c r e t i o n were measured i n Glaucous-winged G u l l s , Larus glaucescens. T o t a l body water volume and turnover r a t e were measured i n b i r d s d r i n k i n g f r e s h water and d r i n k i n g sea water by THO d i s -appearance r a t e . Na +, K +, and CI e x c r e t i o n s over 24 hours were measured by continuous c o l l e c t i o n of c l o a c a l and s a l t gland e x c r e t i o n s from b i r d s fed f i s h , f i s h p l u s a s a l t l o ad, or a s a l t l o a d o n l y . 2. T o t a l body water volume was found to be 79% of body weight on both f r e s h water and sea water d r i n k i n g regimes. TBW volume i s l a r g e compared to other b i r d s . 3. Mean t o t a l body water turnover r a t e was the same f o r b o t h ' d r i n k i n g regimes (0.064 ml/g-day); t h i s value i s the same as the p r e d i c t e d r a t e based on data from other b i r d s . 4. There were no s i g n i f i c a n t d i f f e r e n c e s between the f i s h and f i s h s a l t fed b i r d s i n the p a t t e r n or amounts of i o n e x c r e t i o n . 5. Sodium and c h l o r i d e were e x c r e t e d i n approximately equal amounts from the s a l t gland and c l o a c a . Most potassium was e x c r e t e d v i a the c l o a c a . T h i r t y - e i g h t percent of the t o t a l sodium, 6% of the t o t a l potassium and 58% of the t o t a l c h l o r i d e e x c r e t e d were con t a i n e d i n the s a l t gland s e c r e t i o n of both the f i s h and f i s h + s a l t groups of g u l l s . i i i 6. The f l u i d and s o l i d p o r t i o n s of the c l o a c a l e x c r e t i o n were analyzed f o r i o n s . C a t i o n s were d i v i d e d between the two p o r t i o n s . In the f i s h and f i s h + s a l t f ed b i r d s , 51.8 + 7.8% of the c l o a c a l N a + and 61.8 + 4.5% of the c l o a c a l K + was found i n the s o l i d p o r t i o n of the c l o a c a l e x c r e t a . C h l o r i d e was d e t e c t e d i n the f l u i d p o r t i o n o n l y . 7. The two b i r d s given only a s a l t l o a d had lower r a t e s of e v a p o r a t i v e water l o s s and s m a l l e r amounts of c l o a c a l s o l i d s compared to the fed b i r d s . 8. The l a r g e TBW volume may be advantageous to marine b i r d s as a b u f f e r a g a i n s t excess s a l t i n g e s t i o n . The con-stancy of TBW turnover r a t e suggests t h a t the g u l l s are s p e c i f i c a l l y adapted to t h e i r environment where s a l t , but not water, i s a s t r e s s . 9. The r e s u l t s suggest t h a t the s a l t gland, c l o a c a l f l u i d s and e s p e c i a l l y the c l o a c a l s o l i d s are important routes f o r i o n e x c r e t i o n f o r fed b i r d s and t h a t osmoregulatory pro-cesses f o r fed and unfed b i r d s may be d i f f e r e n t . 10. These data imply t h a t although the s a l t gland i s the primary a d a p t a t i o n of marine b i r d s to s a l t s t r e s s , the e n t i r e process of s a l t and water metabolism a l s o i n v o l v e s o t h e r more s u b t l e mechanisms. i v TABLE OF CONTENTS Page TITLE PAGE . . i ABSTRACT i i TABLE OF CONTENTS i v LIST OF TABLES v i LIST OF FIGURES v i i LIST OF APPENDICES v i i i ACKNOWLEDGEMENTS i x I. INTRODUCTION 1 I I . MATERIALS AND METHODS 6 A. Maintenance of experimental animals . . . . 6 B. T o t a l body water t u r n o v e r — e x p e r i m e n t a l procedures 6 1. Experimental regime 6 2. A n a l y t i c a l procedures . . . . . . . . . 7 a. Sample p r e p a r a t i o n & c o u n t i n g . . . . 7 b. C a l c u l a t i o n s 8 c. A l l o m e t r i c a n a l y s i s 9 C. Ions and water i n s a l t gland s e c r e t i o n and c l o a c a l e x c r e t a — e x p e r i m e n t a l procedures 9 1. Experimental regime 9 2. Sample p r e p a r a t i o n 12 a. S a l t gland s e c r e t i o n 12 b. C l o a c a l e x c r e t i o n 12 c. Ion a n a l y s i s 14 d. E s t i m a t i o n o f s e c r e t i o n volume . . . 15 e. E s t i m a t i o n o f e v a p o r a t i v e water l o s s (EWL) 15 f. D i s c r i m i n a t i o n between s e c r e t o r s and n o n s e c r e t o r s 16 3. S t a t i s t i c a l analyses 16 V Page I I I . RESULTS . 17 A. T o t a l body water tu r n o v e r . 17 1. B i r d weights 17 2. TBW volume 17 3. TBW turnover 17 4. A l l o m e t r i c comparisons 20 a. TBW volume 20 b. TBW turnover 20 B. S a l t gland and c l o a c a 24 1. Ion and f l u i d output 24 2. D i s t r i b u t i o n o f i o n e x c r e t i o n 24 C. Ion P a r t i t i o n i n g Between C l o a c a l F l u i d and S o l i d P o r t i o n s 24 D. E v a p o r a t i v e water l o s s 30 E. Comparison between s a l t gland s e c r e t o r s and non s e c r e t o r s 30 IV. DISCUSSION 34 A. T o t a l body water volume and turnover r a t e 34 B. Ions and water i n s a l t gland s e c r e t i o n and c l o a c a l e x c r e t i o n . . . . 37 C. Conclus i o n s 46 V. SUMMARY . 49 REFERENCES 52 APPENDICES 56 v i LIST OF TABLES Table Page I T o t a l body water volume and turnover r a t e s f o r Glaucous-winged G u l l s , Larus glaucescens (+ SEM) 18 II Comparison of t o t a l body water volume among avian s p e c i e s 22 I I I Ion content of s a l t gland s e c r e t i o n and c l o a c a l e x c r e t i o n c o l l e c t e d over 24 hours from Glaucous-winged G u l l s , Larus glaucescens g i v e n e i t h e r f i s h , f i s h + s a l t , o r s a l t o n l y . The values are presented as means + SEM 25 IV Weight and i o n c o n c e n t r a t i o n of f l u i d and s o l i d p o r t i o n s o f c l o a c a l e x c r e t a c o l l e c t e d over 24 hours from Glaucous-winged G u l l s , Larus glaucescens given e i t h e r f i s h , f i s h + s a l t , or s a l t o n l y . The values are presented as means + SEM 29 V E v a p o r a t i v e water l o s s d u r i n g 24 hours from Glaucous-winged G u l l s , Larus  glaucescens fed f i s h , f i s h + s a l t , or s a l t o n l y . Data values are means + SEM 7 31 VI Ion content of s a l t gland and c l o a c a l i o n e x c r e t i o n : amount of i o n (yeq) e x c r e t e d per 24 hours by s e c r e t i n g and n o n s e c r e t i n g Glaucous-winged G u l l s , Larus glaucescens. The values are means + SEM 32 VII Weight and i o n c o n c e n t r a t i o n s of f l u i d and s o l i d p o r t i o n s of c l o a c a l e x c r e t a c o l l e c t e d over 24 hours from s e c r e t i n g and n o n s e c r e t i n g Glaucous-winged G u l l s , Larus glaucescens 33 V I I I Comparison of 24 hour water and i o n output i n G u l l s , Larus glaucescens, and Ducks, Anas platyrhynchos . . . 44 v i i LIST OF FIGURES Fi g u r e Page 1 Apparatus f o r 24 hour s a l t gland and c l o a c a l e x c r e t i o n c o l l e c t i o n s 11 2 Flow diagram i n d i c a t i n g methods of s e p a r a t i o n and a n a l y s i s of c l o a c a l samples 13 3 Loss o f t r i t i a t e d water (THO) from the e x t r a c e l l u l a r f l u i d o f one Glaucous-winged G u l l (#4) over a two week p e r i o d . . 19 4 R e l a t i o n s h i p between t o t a l body water (TBW) volume and body weight (W) 21 5 R e l a t i o n s h i p between t o t a l body water (TBW) turnover r a t e and body weight (W) f o r a v a r i e t y of a v i a n s p e c i e s . . . . 23 6 The p a r t i t i o n i n g of ions and water i n 24 hour s a l t and c l o a c a l c o l l e c t i o n s from Glaucous-winged G u l l s , Larus  glaucescens presented as percentages of t o t a l i o n and water e x c r e t i o n 26 7 R e l a t i o n s h i p between c a t i o n concentra-t i o n s i n the f l u i d p o r t i o n and s o l i d p o r t i o n of the c l o a c a l e x c r e t i o n 2 8 v i i i LIST OF APPENDICES Appendix Page I Computer program 56 II Data from i n d i v i d u a l b i r d s f o r i o n and f l u i d e x c r e t i o n d u r i n g a 24 hour c o l l e c t i o n p e r i o d 58 I I I E f f e c t s of TBW volume on the estimated osmotic e f f e c t s of a h y p e r t o n i c s a l t l o a d 62 i x ACKNOWLEDGEMENTS Many people have c o n t r i b u t e d to t h i s r e s e a r c h p r o j e c t . Those who loaned equipment, gave advice or helped w i t h com-put e r programming i n c l u d e Dr. John E. P h i l l i p s , Dr. Ian McEwen, Dr. P i e r r e K l e i b e r , Dr. John Gutknecht, Dr. Timothy B r a d l e y , Joan Meredith, W i l l i a m H o l t , Dolores L a u r i e n t e , S t e l l a Coubaraki and Sandra A l l i s o n . Dolores L a u r i e n t e a l s o very generously ran and a p p r o p r i a t e l y a l t e r e d computer programs i n my absence. Sarah Grove i s to be thanked f o r p r o v i d i n g her own f i e l d o b s e r v a t i o n s . Numerous people supported me i n d i v e r s e ways d u r i n g t h i s r e s e a r c h p e r i o d . Mary Perk i n s and Sue Krepp are to be p a r t i c u l a r l y remembered f o r the many times they helped with f e e d i n g and c a r i n g f o r the g u l l s . Many f r i e n d s e s p e c i a l l y my p a r e n t s , Michael S w i f t , Don M a n s f i e l d , C h r i s French, Nick Roe, and Nancy K l e i b e r c o n s i s t e n t l y sup-p o r t e d and encouraged my e f f o r t s i n t h i s p r o j e c t . My super-v i s o r , Dr. Maryanne R. Hughes i s to be thanked f o r her moral support as w e l l as p r o v i s i o n of l a b o r a t o r y space, advice and c r i t i c i s m , and s h a r i n g much of her l a b o r a t o r y experience w i t h me. I g r e a t l y a p p r e c i a t e the care given to t h i s manuscript by i t s t y p i s t , Mrs. Peggy E l l i s . F i n a n c i a l support f o r t h i s r e s e a r c h was p r o v i d e d by the N a t i o n a l Research C o u n c i l of Canada grant A-3442 awarded to Dr. M. R. Hughes •. i n the Department of Zoology. 1 I. INTRODUCTION The osmoregulatory problems faced by marine b i r d s are determined by t h e i r environment which combines aspects of the o c e a n i c and t e r r e s t i a l environments. Water i s abun-dant but o f t e n s a l t y ; the g u l l ' s d i e t of f i s h and crustaceans i s high i n p r o t e i n and can be h y p e r t o n i c with r e s p e c t to the b i r d ' s body f l u i d s ; t e r r e s t i a l l i f e imposes o b l i g a t o r y water l o s s e s due to r e s p i r a t o r y e v a p o r a t i o n and e x c r e t i o n o f excess s a l t s , n i t r o g e n and oth e r metabolic wastes. In sum, these b i r d s need to ex c r e t e l a r g e amounts of s a l t and s m a l l amounts o f water t o remain i n s a l t and water balance. T h i s r e q u i r e s e x c r e t i o n o f h y p e r t o n i c s a l t s o l u t i o n s . The av i a n kidney can, but r a r e l y does, produce a u r i n e c o n t a i n i n g h y p e r t o n i c l e v e l s o f sodium or c h l o r i d e (Hughes, 19 70; Farner & King, 1972). In marine b i r d s , i t i s the s a l t gland, l o c a -t e d i n the head o f the b i r d , t h a t e l i m i n a t e s excess s a l t as a h y p e r t o n i c s a l t s e c r e t i o n (Schmidt-Neilsen, e t a l . , 1958). Even though the s a l t gland p r o v i d e s an adequate means f o r h y p e r t o n i c NaCl e x c r e t i o n , i t i s p o s s i b l e t h a t marine b i r d s a l s o use oth e r mechanisms t o cope wi t h s a l t l o a d i n g . There are two p h y s i o l o g i c a l parameters which i n f l u e n c e osmoregula-t i o n — 1 ) r a t e and routes o f water turnover, and, 2) r a t e and routes o f s a l t t urnover. 2 T o t a l body water (TBW) turnover r a t e i s i n d i c a t i v e of the f l u x o f water through an organism. I t i s a f u n c t i o n of d r i n k i n g r a t e , e v a p o r a t i o n r a t e , and the r a t e of water e x c r e t i o n — v a r i a b l e parameters t h a t are interdependent ( i . e . , e i n p u t s = e o u t p u t s ) . Changes i n TBW turnover r a t e and volume between f r e s h water and sea water d r i n k i n g regimes may be taken as i n d i c e s o f a d a p t a t i o n to sea water i n g e s t i o n . I f marine b i r d s are s i m i l a r to p a s s e r i n e s , t h a t commonly d r i n k s a l t or b r a c k i s h water, no changes i n d r i n k i n g r a t e o r , by e x t r a p o l a t i o n , i n TBW turnover r a t e i s expected ( B a r t h o l o -mew & Cade, 1963). A second means of i n d i c a t i n g whether o v e r a l l water metabolism i s u n i q u e l y adapted to or s t r e s s e d by the marine environment i s to compare TBW volume and turnover r a t e f o r t h i s s p e c i e s to those f o r o t h e r s p e c i e s by means of a l l o m e t r i c e quations. V a r i a t i o n s from values p r e d i c t e d by the equations generated from data on other avian s p e c i e s o f t e n i n d i c a t e s p e c i f i c environmental a d a p t a t i o n s . TBW t u rnover r a t e was measured twice i n a group of Glaucous-winged G u l l s , Larus  glaucescens, f i r s t , d u r i n g a freshwater d r i n k i n g regime and second, d u r i n g a seawater d r i n k i n g regime. The two s e t s of measurements were compared to determine i f the g u l l s do modify d r i n k i n g r a t e i n response to the type of d r i n k i n g water a v a i l -a b l e . The e f f e c t of d r i n k i n g seawater on TBW turnover was then compared to non-marine b i r d s 1 responses to seawater i n g e s t i o n . The values f o r TBW turnover r a t e were a l s o compared 3 to those o f other a v i a n s p e c i e s by a l l o m e t r i c a n a l y s i s to determine i f the turnover r a t e s measured are unique to the g u l l s . S a l t gland s e c r e t i o n i s o f t e n c o n s i d e r e d to occur o n l y i n response t o a s a l t l o a d . However, t h e r e are a t l e a s t two i n d i c a t i o n s t h a t the s a l t gland must p a r t i c i p a t e i n normal s a l t s e c r e t i o n . F i r s t l y , spontaneous s a l t s e c r e t i o n s have been r e p o r t e d (Hughes, 1970; Grove, p e r s . comm.), and secondly, the amounts of i o n ex c r e t e d i n spontaneously voided c l o a c a l samples are too low to account f o r the e x c r e t i o n o f d i e t a r y s a l t s (Hughes, 1970, 1972a). However, the r e l a t i v e r o l e s of these two routes have not been measured f o r marine b i r d s under normal f e e d i n g regimes. T h e r e f o r e , i n the presen t study, r e l a t i v e r a t e s o f e x t r a r e n a l and r e n a l monovalent i o n e x c r e t i o n were measured by c o l l e c t i n g s a l t gland s e c r e t i o n s and c l o a c a l e x c r e t a f o r a 24 hour p e r i o d from f ed g u l l s . Three i n v e s t i g a t o r s (Johnson, 1969; Hughes, 1972b; McNabb e t a_l. , 1973) have measured s i g n i f i c a n t f r a c t i o n s of ions bound t o c l o a c a l s o l i d s i n hawks, young k i t t i w a k e s and domestic fowl r e s p e c t i v e l y , but these ions have not been con-s i d e r e d i n most s a l t and water balance s t u d i e s . Since these p r e c i p i t a t e d ions do not c o n t r i b u t e t o the osmotic p r e s s u r e of the c l o a c a l f l u i d , they r e p r e s e n t a p o r t i o n of ions t h a t can be e x c r e t e d without any accompanying water. In t h i s study, the c l o a c a l m a t e r i a l was d i v i d e d i n t o two p o r t i o n s to assess the percentage of c l o a c a l l y e x c r e t e d ions i n s o l u t i o n compared 4 to ions p r e c i p i t a t e d with the s o l i d c l o a c a l c o n t e n t s . The exten t to which monovalent ions are exc r e t e d by the s a l t gland and p r e c i p i t a t e d i n the s o l i d p o r t i o n o f the c l o a c a l e x c r e t a are i n d i c e s o f how w e l l the b i r d i s adapted to con-serve water w h i l e e x c r e t i n g s a l t s . I t was decided to do these experiments wi t h fed b i r d s i n order t o simulate a n a t u r a l p h y s i o l o g i c a l s t a t e . Since f e e d i n g i n c r e a s e s p r o t e i n a s s i m i l a t i o n and probably a l t e r s the r a t e o f i o n uptake from the gut, i t i s expected to a f f e c t s a l t e x c r e t i o n p a t t e r n s . However, the r o l e of f e e d i n g i n the p a t t e r n o f s a l t e x c r e t i o n has not been q u a n t i f i e d . S a l t glands are a s s o c i a t e d w i t h both marine s p e c i e s and some f a l c o n i f o r m s t h a t i n g e s t high p r o t e i n d i e t s (Cade & Greenwald, 1966). Pro-t e i n metabolism r e s u l t s i n n i t r o g e n e x c r e t i o n , predominately as u r i c a c i d and ammonia (Holmes e t a l . , 1968; McNabb e t a l . , 19 73). The u r i c a c i d i s p r e c i p i t a t e d and combines wi t h mono-v a l e n t ions i n the u r i n e but the ammonia c o n t r i b u t e s to the o s m o l a r i t y o f the u r i n e (as much as 50% of the c a t i o n s ) (Holmes e t a l . , 1968; Johnson, 1969; Douglas, 1970). Douglas (19 70) compared f e d and unfed H e r r i n g G u l l s (Larus argentatus) i n terms of t h e i r response to an e q u i v a l e n t s a l t l o a d (10% body weight of sea water) given by stomach tube. Although the percentage of each l o a d l o s t v i a each route i n 3.5-4.0 hours was s i m i l a r i n both cases, the amount of f l u i d l o s t c l o a c a l l y by the f e d b i r d s was n e a r l y twice t h a t l o s t by the unfed b i r d s . Douglas d i d not determine the i o n content o f the s o l i d c l o a c a l 5 m a t e r i a l . Since an u n p h y s i o l o g i c a l l y l a r g e s a l t l o a d was administered and the bound c l o a c a l ions not determined, Douglas's study does not r e a l l y address i t s e l f to the r o l e of fe e d i n g on the normal p a r t i t i o n i n g of s a l t and water e x c r e t i o n by a b i r d under n a t u r a l c o n d i t i o n s . Thus, i n the present study, two b i r d s were giv e n only a s a l t l o a d and s u b j e c t e d to the same 24-hour c o l l e c t i o n as the fed b i r d s i n order to assess the e f f e c t of f e e d i n g on the p a t t e r n of s a l t e x c r e t i o n . N 6 I I . MATERIALS AND METHODS A. Maintenance o f Experimental Animals The Glaucous-winged G u l l s (Larus glaucescens) used d u r i n g t h i s study were ob t a i n e d as f l e d g l i n g s i n 1973 and h e l d i n the v i v a r i u m of the U n i v e r s i t y o f B r i t i s h Columbia. Three to f i v e b i r d s were h e l d i n each o f 4 wire mesh cages (2m long X 1.2m wide X 0.76m h i g h ) . The b i r d s ' wings and t a i l f e a t h e r s were kept c l i p p e d to prevent f l y i n g and c o l o r e d p l a s t i c i d e n -t i f i c a t i o n bands were p l a c e d on t h e i r l e g s . Each b i r d was fed b a i t h e r r i n g (Clupea p a l a s i i ) (approximately 60 g) d a i l y and given a m u l t i p l e v i t a m i n supplement about every 5 days. Water f o r b a t h i n g and d r i n k i n g was pr o v i d e d i n 2 p l a s t i c dishpans i n each cage. The water was changed and the cages washed d a i l y . B. T o t a l Body Water T u r n o v e r — E x p e r i m e n t a l Procedures 1. Experimental regime. Seven b i r d s were s t u d i e d u s i n g the f o l l o w i n g e x p e r i -mental procedure. Each b i r d was weighed and p l a c e d on a r e s t r a i n i n g board. A 1.0 ml blood sample was taken from 1 l e g v e i n u s i n g a 1.0 ml h e p a r i n i z e d t u b e r c u l i n s y r i n g e . Then, 2.5 or 3.0 mci THO (spec. a c t . = 100 mci/g, New England Nuclear) i n 0.5 ml of i s o t o n i c s a l i n e was slo w l y i n j e c t e d i n t o the c o n t r a l a t e r a l l e g v e i n t a k i n g care to prevent back-flow o f l a b e l e d b l o o d . The b i r d was r e t u r n e d to i t s cage. 7 A f t e r 4 hours (time d e s i g n a t e d t ) a 1.0 ml b l o o d sample was taken. The b i r d was r e t u r n e d to i t s cage, f e d , and, t h e r e -a f t e r maintained on i t s normal f e e d i n g and water regime. Blood samples were taken from a l t e r n a t e l e g s every other day f o r the next 2 weeks. F o l l o w i n g completion of the s e r i e s of b l o o d samples f o r TBW measurement on a freshwater regime, these b i r d s were g r a d u a l l y adapted over a p e r i o d of 1 month to f u l l s t r e n g t h sea water. A f t e r 1 week on f u l l s t r e n g t h sea water, the pro-cedure d e s c r i b e d above was repeated w h i l e the b i r d s were main-t a i n e d on sea water. Body weight was measured a t the end of the experiment. One b i r d (#5) d i e d e a r l y i n t h i s phase of the experiment l e a v i n g 6 b i r d s i n the study. 2. A n a l y t i c a l procedures a. Sample p r e p a r a t i o n and c o u n t i n g Immediately a f t e r a b l o o d sample was taken, i t was t r a n s f e r r e d to a l a b e l l e d 1.0 ml c e n t r i f u g e tube and spun a t 6000 rpm i n an I n t e r n a t i o n a l Model HN C e n t r i f u g e f o r 6 minutes. An 0.1 ml a l i q u o t o f each plasma sample was added to 10 ml o f @ Aquasol s c i n t i l l a t i o n c o c k t a i l (New England Nuclear) i n low potassium g l a s s c o u n t i n g v i a l s (Wheaton S c i e n t i f i c ) and shaken v i g o r o u s l y by hand. Any e f f e c t of plasma p r o t e i n s on cpm was excluded by c o n t r o l samples u s i n g TCA p r e c i p i t a t e d plasma t h a t was n e u t r a l i z e d by NaOH. The samples were s e a l e d and s t o r e d i n opaque covered c o n t a i n e r s i n the r e f r i g e r a t o r 8 f o r a t l e a s t 2 4 hours p r i o r to c o u n t i n g to allow time f o r d i s i n t e g r a t i o n o f a l l s c i n t i l l a t i o n s due to l i g h t i n t e r a c t i o n s w i t h b i o l o g i c a l compounds. Care was taken not to expose samples to l i g h t p r i o r to c o u n t i n g . An ISOCAP 300 l i q u i d b eta counter (Nuclear Chicago) w i t h programmed window s e l e c t i o n s was used t o count a l l samples. Samples were counted f o r 10 minutes (to a maximum o f 10 counts) and recorded as counts per minute (cpm). Quench curves were generated by repeated c o u n t i n g of @ THO s p i k e d Aquasol to which i n c r e a s i n g amounts (0.0-1.0 ml) of a v i a n plasma were added. Subsequent to each plasma a d d i -t i o n , the sample was s t o r e d i n darkness f o r 24 hours and c o u n t i n g was repeated 5 times. Raw counts were converted to d i s i n t e g r a t i o n s per minute (dpm) by r e f e r e n c e to these quench curves. b. C a l c u l a t i o n s The c a l c u l a t i o n s and data p l o t t i n g were done with the a i d o f a PDP 11/45 computer ( D i g i t a l C o r p o r a t i o n ) . The pro-gram i s l i s t e d i n Appendix I. TBW volume was c a l c u l a t e d from the d i l u t i o n o f i n j e c t e d THO a t t . J o A s i g n t e s t f o r p a i r e d samples was used to compare the values o b t a i n e d from the b i r d s d u r i n g the freshwater and sea-water d r i n k i n g regimes ( L a r k i n , 19 74). Means and standard e r r o r of the mean (SEM) were determined f o r TBW volume and turnover r a t e on a Programmable Hewlett Packard C a l c u l a t o r (Model #9100b). 9 c. A l l o m e t r i c a n a l y s i s Values f o r TBW volume and TBW turnover r a t e d e t e r -mined by e i t h e r THO l o s s or from the d r i n k i n g r a t e were ob-t a i n e d from the l i t e r a t u r e f o r a number of a v i a n s p e c i e s . L i n e a r r e g r e s s i o n analyses of the l o g a r i t h i m s of TBW volume and TBW turnover r a t e on the l o g a r i t h i m of body weight were done with the a i d of a PDP 15 ( D i g i t a l Corporation) computer to o b t a i n equations i n the form: l o g Y = a + b l o g W where Y i s TBW volume or turnover r a t e , W i s weight of the b i r d i n grams, and a and b are the i n t e r c e p t and slope of the r e g r e s s i o n l i n e . C. Ions and Water i n S a l t Gland S e c r e t i o n and C l o a c a l E x c r e t a — E x p e r i m e n t a l Procedures 1. Experimental regime On the day of an experiment the b i r d was fed a p r e -weighed h e r r i n g ( S a r t o r i u s : Kilomat balance) at i t s normal f e e d i n g time. I t was hand-fed or observed u n t i l the f i s h was eaten to i n s u r e t h a t the a p p r o p r i a t e b i r d ate the e n t i r e f i s h . I f the b i r d was to be given an e x t r a s a l t l o a d , a g e l a t i n capsule c o n t a i n i n g 7.35 meq NaCl was p l a c e d i n the f i s h p r i o r to f e e d i n g . The b i r d was l e f t alone f o r the next 4 hours, the minimum time r e q u i r e d f o r s u f f i c i e n t d i g e s t i o n of the f i s h to prevent r e g u r g i t a t i o n , the b i r d ' s normal f r i g h t response. 10 The b i r d was weighed, p l a c e d i n a s o f t c l o t h r e s t r a i n i n g s l i n g and h e l d i n an u p r i g h t p o s i t i o n w i t h i n the c o n f i n e s of a wooden frame (Figure 1). The b i r d s given o n l y the s a l t l o a d were weighed and p l a c e d i n the r e s t r a i n i n g s l i n g p r i o r to s a l t l o a d i n g . Three g e l a t i n capsules c o n t a i n i n g a t o t a l of 3200 yeq Na, +5000 yeq K + and 8200 yeq C l ~ were p l a c e d i n the b i r d ' s g u l l e t f o l l o w e d by 50 ml of d i s t i l l e d water given by stomach tube. The b i r d remained i n the s l i n g but c o l l e c t i o n s a l t gland s e c r e t i o n and c l o a c a l f l u i d was not begun f o r 4 hours C l o a c a l samples were c o l l e c t e d i n a preweighed con-t a i n e r t h a t f i t t e d over the rump of the g u l l . The c o n t a i n e r was an i n v e r t e d 1 g a l l o n p l a s t i c b o t t l e with a hole cut i n the s i d e and a p i e c e of p l a s t i c s c r e e n i n g p l a c e d over the mouth beneath the screw cap. S a l t gland s e c r e t i o n was c o l l e c t e d by p l a c i n g a second p l a s t i c b o t t l e (with the base removed and a i r - h o l e s cut i n both ends) over the head of the b i r d . Both b o t t l e s were suspended from wooden frame and were attac h e d t o each other and to the s l i n g worn by the b i r d so t h a t the b i r d c a r r i e d both c o n t a i n e r s w i t h i t i f i t moved. Temperature and humidity were recorded a t i n t e r v a l s throughout the 24 hour p e r i o d . At the end of t h i s time, the b i r d ' s nares were washed with d i s t i l l e d water by means of a long d i s p o s a b l e p i p e t t e i n s e r t e d through the mouth of the b o t t l e . The 2 c o n t a i n e r s were removed and the b i r d was immediately reweighed and r e t u r n e d to i t s cage. 11 F i g u r e 1. Apparatus f o r 2 4-hour s a l t gland and c l o a c a l e x c r e t i o n c o l l e c t i o n s . G u l l i s p l a c e d i n a c l o t h s l i n g (shaded) which i s suspended from the wooden frame by f l e x i b l e c o r d (dotted l i n e s ) . The c o n t a i n -e r s (1 g a l l o n p l a s t i c jugs w i t h e i t h e r the bottom or s i d e removed) are supported by the frame and attached to the s l i n g by c o r d (dotted l i n e s ) . A b i t of p l a s t i c s c r e e n i n g was p l a c e d over the mouth of the c o n t a i n e r f o r c l o a c a l samples and h e l d i n p l a c e by a rubber band at the neck and the l i d of the c o n t a i n e r . The c i r c l e s on the c o n t a i n e r over the b i r d ' s head r e p r e -sent a i r - h o l e s . A fan was p l a c e d to draw a i r forward through t h i s c o n t a i n e r . The b i r d ' s weight i s supported but i t may walk to and f r o w i t h i n the frame. 11a 12 2. Sample p r e p a r a t i o n a. S a l t gland s e c r e t i o n At the end of the c o l l e c t i o n p e r i o d the c o n t a i n e r was r i n s e d with 25 or 30 ml of 15 meq/1 L i C l . T h i s sample was fr o z e n i n a s e a l e d c o n t a i n e r and analysed a t a l a t e r date f o r t o t a l sodium, potassium and c h l o r i d e content. The recovery of s a l t on the c o n t a i n e r w a l l s was 95% f o r sodium and 101% f o r c h l o r i d e i n 3 t r i a l s w i t h s p i k e d c o n t a i n e r s . b. C l o a c a l e x c r e t i o n The p l a s t i c b o t t l e used f o r c o l l e c t i n g c l o a c a l e x cre-t i o n was weighed immediately a f t e r removal from the b i r d and the i n c r e a s e i n weight was taken as the t o t a l amount of m a t e r i a l e x c r e t e d by the c l o a c a i n the 24 hour p e r i o d . The procedure o u t l i n e d i n the flow diagram (Figure 2) was m o d i f i e d s l i g h t l y from Hughes (1972b). The f l u i d and s o l i d p o r t i o n s of the c l o a c a l sample were i n i t i a l l y separated by a l l o w i n g the sample to f i l t e r f o r 1 hour through the screen i n t o a pre-weighed v i a l . The v i a l was reweighed to determine the weight of f l u i d e x c r e t a . The remaining m a t e r i a l was scraped from the s i d e s o f the c o n t a i n e r and 50 ml of d i s t i l l e d water was used to r i n s e the c o n t a i n e r . T h i s f l u i d was d r a i n e d through the screen i n t o a c o l l e c t i o n b o t t l e to form the 'wash' p o r t i o n o f the sample. T h i s was r e f r i g e r a t e d o v e r n i g h t t o allow s e t t l i n g o f the sus-pended s o l i d s . The 'wash' was subsequently f i l t e r e d through pre-weighed Whatman #1 f i l t e r paper and the m a t e r i a l on the 13 j F i g u r e 2. Flow diagram i n d i c a t i n g methods of s e p a r a t i o n and a n a l y s i s o f c l o a c a l samples. Processes are l i s t -ed on the l e f t - h a n d s i d e and p o r t i o n s t h a t were sub-sequently analyzed f o r i o n contents are underscored on the ri g h t - h a n d s i d e o f the diagram. 13a CLOACAL SAMPLE weigh & f i l t e r through screen scrape & r i n s e c o n t a i n e r w i t h d i s t i l l e d H 2 0 scrape m a t e r i a l from screen and w a l l s of c o n t a i n e r onto f i l t e r paper F l u i d p o r t i o n Wash p o r t i o n f i l t e r through Whatman #1 f i l t e r paper S o l i d p o r t i o n (1) S o l i d p o r t i o n (2) •Values f o r i o n a n a l y s i s incomplete and low, t h e r e f o r e not i n c l u d e d i n computations o f i o n output. 14 f i l t e r paper was d r i e d to constant weight ( s o l i d #1). The f i l t r a t e was s t o r e d and l a t e r analyzed f o r i o n content. The f i n a l p o r t i o n ( s o l i d #2) of the c l o a c a l sample c o n s i s t e d of e v e r y t h i n g t h a t was l e f t i n the c o n t a i n e r a f t e r the washing procedure. These s o l i d s were scraped onto a p i e c e of pre-weighed f i l t e r paper,- f e a t h e r s , i f present, were removed, and the sample d r i e d to constant weight. These 2 d r i e d p o r t i o n s were i n d i v i d u a l l y ground to a f i n e powder wi t h a mortar and p e s t l e and an 0.25 g p o r t i o n of the powder was t r a n s f e r r e d to a 100 ml stoppered v o l u m e t r i c f l a s k c o n t a i n i n g 75 ml of 0.5% LiGO making a d i l u t e s l u r r y with a pH g r e a t e r than 8. The f l a s k s were shaken o v e r n i g h t and the contents f i l t e r e d through Whatman #1 paper. A 2.0 ml a l i q u o t of the f i l t r a t e was d i l u t e d w i t h 8.0 ml of d i s t i l l e d water and analyzed f o r sodium and potassium c o n c e n t r a t i o n s . For c h l o r i d e a n a l y s i s , 5 ml of the f i l t r a t e was evaporated to dryness and then resuspended i n 1 ml of d i s t i l l e d water, c. Ion a n a l y s i s Sodium and potassium c o n c e n t r a t i o n s were measured by i n t e r n a l standard flame photometry using an Instrumentation L a b o r a t o r i e s Model 14 3 flame photometer. A l i q u o t s of the s a l t gland s e c r e t i o n and the c l o a c a l f l u i d s were d i l u t e d with 15 m e q / L i C l t o b r i n g i o n c o n c e n t r a t i o n s w i t h i n r e a d i n g range of the flame photometer. The l i t h i u m i n the d i l u t e d L i C 0 3 s o l u t i o n used to d i s s o l v e the s o l i d p o r t i o n s of the c l o a c a l samples d e s c r i b e d above served as the i n t e r n a l standard f o r these samples. 15 C h l o r i d e was measured wi t h a CMT 10 C h l o r i d e t i t r a t o r (Radiometer, Copenhagen) u s i n g 20 y l a l i q u o t s of sample s o l u t i o n s . Ion content of the f i s h was c a l c u l a t e d from the weight of the f i s h , the water content (61.6% body weight, n = 3) and the f o l l o w i n g i o n c o n c e n t r a t i o n s determined f o r h e r r i n g (Clupea p a l a s i i ) by Hughes (1972b): 82 meq/1 Na +, 124 meq/1 K +, and 69 meq/1 C l ~ . d. E s t i m a t i o n o f s e c r e t i o n volume S a l t gland s e c r e t i o n volume was estimated by d i v i d i n g the t o t a l observed N a + and CI outputs by the c o n c e n t r a t i o n s of these 2 ions i n spontaneous s e c r e t i o n s from n o n - s a l t - l o a d e d b i r d s r e p o r t e d by Hughes (1972b) to be 375 meq Na +/1 and 463 meq CI / l . These are probably minimal c o n c e n t r a t i o n s as the b i r d s i n Hughes' study had not r e c e n t l y i n g e s t e d any i o n s ; t h e r e f o r e , these low c o n c e n t r a t i o n s should p r e d i c t a maximal s e c r e t i o n volume f o r b i r d s i n t h i s study. For each b i r d , the s e c r e t i o n volume was assigned as the mean of the values o b t a i n -ed from Na + and CI output as f o l l o w s : _ I t o t a l Na yeq obs. t o t a l CI yeq obs. V O i e s t L 3 7 5 y e q N a / m l 4 6 3 ^ e c5 Cl/ml e. E s t i m a t i o n of e v a p o r a t i v e water l o s s (EWL) The volume of water l o s t by e v a p o r a t i o n was assumed to be equal to the weight l o s s d u r i n g the 24 hour p e r i o d t h a t was not accounted f o r by other e x c r e t a , i . e . , 16 EWL = AW - W , ,+ W c l o a c a l s.g. where AW i s the change i n body weight, W , , i s the weight C X O c L C EL X of the t o t a l c l o a c a l e x c r e t a and W i s the c a l c u l a t e d s.g. weight of s a l t gland s e c r e t i o n s assuming the volume determined above and 1 g/ml f l u i d . f . D i s c r i m i n a t i o n between s e c r e t o r s and n o n s e c r e t o r s S e c r e t o r s from a l l 3 groups were a r b i t r a r i l y d e f i n e d as b i r d s w i t h a c a l c u l a t e d s e c r e t i o n volume - 1 ml. T h i s value was chosen as there was a d i s t i n c t s e p a r a t i o n i n the d i s t r i b u t i o n of s e c r e t i o n volumes at 1 ml. 3. S t a t i s t i c a l analyses A l l i o n p a r t i t i o n i n g c a l c u l a t i o n s and s t a t i s t i c s c a l -c u l a t i o n s were done u s i n g c a l c u l a t o r s (Monroe, Hewlett Packard programable c a l c u l a t o r 9100B) or a computer (PDP 15, D i g i t a l C o r p o r a t i o n ) . A nonparametric s t a t i s t i c a l t e s t , the Mann Whitney U T e s t ( S i e g e l , 1956) was chosen to determine d i f f e r e n c e s between sample groups. The data on b i r d s given f i s h + s a l t and the b i r d s given o n l y s a l t were compared wi t h data on b i r d s fed only f i s h . B i r d s which s e c r e t e d were compared with those t h a t d i d not. Values are presented as means + standard e r r o r of the mean (SEM). 17 I I I . RESULTS A. T o t a l Body Water Turnover Body weights, TBW volumes, and TBW turnover r a t e s f o r each g u l l and the mean values f o r both the freshwater and seawater d r i n k i n g regimes are presented i n Table I. 1. B i r d weights Body weights (W) of the b i r d s d i d not vary s i g n i f i -c a n t l y between treatments. Mean body weight f o r the f r e s h -water regime was 76 3 + 4 6 g compared to 817 + 50 g f o r the seawater regime. Mean weight f o r both treatments combined was 787 + 33 g. 2. TBW volume There was no d i f f e r e n c e i n TBW volume between the treatments whether expressed as volume or percent of body weight. The mean value of TBW volume was 81.3 + 4.7% W d u r i n g the freshwater regime and 76.9 + 2.5% W d u r i n g the seawater regime. The mean value of TBW volume f o r the combined t r e a t -ments was 79.3 +2.. 8% W. 3. TBW turnover Rates of turnover v a r i e d c o n s i d e r a b l y between i n d i v i d -u a l s w i t h t.jy 2 v a l u e s r a n g i n g from 4.5 t o 8.3 days. Turnover r a t e s d i d not c o r r e l a t e w i t h body weight as demonstrated by a s i g n t e s t ( L a r k i n , 1974). F i g u r e 3 i s a r e p r e s e n t a t i v e p l o t o f l o g dpm THO as a f u n c t i o n o f time f o r one b i r d d r i n k i n g freshwater and l a t e r 18 TABLE I. T o t a l body water volume and turnover r a t e s f o r Glaucous-winged G u l l s , Larus glaucescens ( + SEM) . B i r d # W (g) TBW (ml) TBW (% W) t ( l / 2 ) (days) F l u x (ml/g-day) Freshwater 1 724 552 76.2 5.28 .072 2 880 510 57.9 6.35 .045 3 684 580 84.4 7.63 .056 4 892 685 76.7 7.51 .051 5 577 515 89.2 6.98 .063 6 707 630 89.1 5.92 .074 7 875 840 96.0 5.33 .089 X 763 616 81.3 6.42 .064 +46 +44 +4.7 +0.37 +0.006 Saltwa t e r 1 711 588 82.7 4.51 .091 2 885 620 70.0 8.01 .043 3 646 525 81.2 6.66 .061 4 c 981 820 83.5 7.27 .057 D 6 802 568 70.8 4.92 .071 7 877 643 73.3 8.33 .060 X 817 627 76.9 6.62 .064 +50 + 42 +2.5 +0.65 +0.007 Combined 787 621 79.3 6.52 .064 +33 +29 +2.8 +0.34 +0.004 gure 3. Loss of t r i t i a t e d water (THO) from the e x t r a -c e l l u l a r f l u i d o f one Glaucous-winged G u l l (#4) over a two week p e r i o d . ( 0 ) = f r e s h water regime and (•) = sea water regime. 19a 0 s a l t water J, 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 k 5 6 7 8 9 10 i i 12 13 i<* TIME (DAYS) 20 saltwater. The slope of the l i n e indicates the rate of water turnover (K). The data presented i n Figure 3 and Table I i n d i -cate that neither the ^ 2_/2' required for one-half the water volume to be replaced, nor the water flux (ml/g-day) were di f f e r e n t for the 2 treatments. Mean water flux for the fresh-water and the seawater regimes were i d e n t i c a l , 0.064 ml/g-day. The t-jy2 f o r T B W turnover was 6.42 + 0.37 days for the fresh-water regime compared with 6.62 + 0.65 days for the seawater regime. 4. Allometric comparisons a. TBW volume Figure 4 i s a plot of log TBW as a function of log W. The equation for the regression l i n e i s : log TBW volume = -0.25 + 1.0 log W (n = 19) (ml H20) (g) The slope of t h i s l i n e was not d i f f e r e n t from 1.0, indicating that the TBW volume i s a d i r e c t function of body weight and that TBW volume may be compared among species as a percentage of body weight as i n Table I I . The two values for g u l l s (indicated by A i n Figure 4) were not included i n ' the regression analysis. One point (this study) i s just within the 95% confidence l i m i t s of the l i n e and the other point (Ruch and Hughes, 1975) i s not within the 95% confidence l i m i t s of the regression l i n e . As t h i s analysis and Table II indicate, g u l l s appear to have a high TBW volume compared to other birds. b. TBW turnover The regression l i n e for TBW turnover on body weight i s presented i n Figure 5. The equation i s : gure 4. R e l a t i o n s h i p between t o t a l body water (TBW) volume and body weight (W). A c t u a l data values used and r e f e r e n c e s are l i s t e d i n Table I I . The two p o i n t s marked A r e p r e s e n t the two Glaucous-winged G u l l s and are not i n c l u d e d i n the r e g r e s s i o n l i n e . TOTAL BUY WATER V O L U e VS- BODY V/EIGHT UDG Y = -0-24B7 + 1*015 * UDG X N = 4000* l/j. urx>. looo* GOUO UDG BODY WEIGHT (G) TABLE I I . Comparison of t o t a l body water volume among avian species. Species n W TBW TBW (g) (ml) (%BW) Speotyto c u n i c u l a r i a hypogaea 1 140 58.7 41.9 Gallus domesticus 5 3490 1888 54.1 G a l l u s domesticus 2 2506 1362 54.3 Columba l i v i a 8 362 202 55.0 A r a t i n g a c a n i c u l a r i s e l o u r n i r o s t r u m 1 313 193 61.3 G a l l u s domesticus (laying) 5 3440 2194 61.6 C o t u r n i x c o t u r n i x japonica 5 117 72.8 61.8 T a e n i o p y g i a c a s t a n o t i s 8 13.4 8.5 63.0 G a l l u s domesticus (laying) 5 3530 2252 63.8 Geococcyx c a l i f o r n i c u s 3 291 217 64t> Anas platyrhynchosH 7 2352 1512 64 G a l l u s domesticus 5 2600 1668 64 G a l l u s domesticus 4 5090 3273 64.3 C o t u r n i x c o t u r n i x japonica 5 105 70 66.5 G a l l u s domesticus 4 4640 3090 66.6 Anas p l a t y r h n c h o s 7 3091 2121 68.5 Gypohierax a n g o l e n s i s 1 1590 1124 70.7 G a l l u s domesticus 4 4900 3474 70.9 Larus glaucescens 6 782 622 79 .4 Larus g l a u c e s c e n s 2 835 735 87.9 Reference Chapman & McFarland (1971) Chapman & Mihai (1972) Ruch & Hughes (1975) LeFebvre (19 64) Chapman & Chapman & Chapman & Skadhauge Chapman & McFarland ( 1 9 7 1 ) Mihai (1972) McFarland ( 1 9 7 1 ) & Bradshaw, 1 9 7 4 ) Mihai (1972) Ohmart, Chapman & Black ( 1 9 7 0 ) Ruch & Hughes (1975) Chapman & Black (1967) Chapman & Mihai (19 72) Chapman & McFarland (19 7 1 ) Chapman & Mihai (1972) Ruch & Hughes (19 75) Chapman & McFarland (19 7 1 ) Chapman & Mihai (19 72) Walter (unpub.) Ruch & Hughes (19 75) aThese birds and values are the same as those used i n Figure 4. ID Ohmart et a l . reported TBW volume = 64% W but t h e i r data on body weight and TBW volume in d i c a t e the value should be 75% W. c Maintained on a saltwater regime (87% seawater). ro 23 F i g u r e 5. R e l a t i o n s h i p between t o t a l body water (TBW) turnover r a t e and body weight (W) f o r a v a r i e t y of a v i a n s p e c i e s . The p o i n t f o r Glaucous-winged G u l l s A determined i n t h i s study i s not i n c l u d e d i n the r e g r e s s i o n l i n e . Values f o r turnover were determined by THO disappearance or by t o t a l water budgets. Species and r e f e r e n c e s are l i s t e d i n order from l e a s t t o g r e a t e s t body weight: Zebra F i n c h , T a eniopygia c a s t a n o t i s (2) (Skadhauge & Bradshaw, 19 74); Inca Dove, S c a r d a f e l l a i n c a (27) (McMillen & T r o s t , 1966); Cowbird, Molothrus a t e r obscurus (9) L u s t i c , 1970) ; C o t u r n i x Q u a i l , C o t u r n i x c o t u r n i x j a p o n i c a (10) (Chapman & McFarland, 1971); White-winged Dove, Zenaida a s i a t i c a a s i a t i c a (17) (McMillen & T r o s t , 1966); Burrowing Owl, Speotyto c u n i c u l a r i a hypogaea (1) (Chapman & McFarland, 1971); Roadrunner, Gococcyx c a l i f o r n i c u s (3) (Ohmart, Chapman & McFarland, 1970) ; Petz Conure, A r a t i n g a c a n c u l a r i s e l o u r n i r o s t r u m (1) (Chapman & McFarland, 1971); Glaucous-winged G u l l , Larus glaucescens (;7):f-(present s t u d y ) ; V u l t u r i n e F i s h E agle, Gypohieraz a n g o l e n s i s (1) (Chapman & McFarland, 1971); White Leghorn Chicken, G a l l u s domesticus ( 5 ) (Chapman & Black, 1967); n o n l a y i n g Rock C o r n i s h Hen, Rock C o r n i s h Rooster G a l l u s domesticus (4) (Chapman & M i h a i , 19 72). 23a TOTAL BODY WATER TLFNOVER RATE V5» BODY WEIGHT LOG Y = -0.3393 + 0*7517 * UDG X N = 13 10. jjCX)- 1000- GOOD. LOG BODY WEIGHT CG) 24 l o g t urnover = -0.40 + 0.75 l o g W (n = 13) (ml H20/day) (g) The value f o r the g u l l s i n t h i s study f e l l w i t h i n the range p r e d i c t e d by body weight. B. S a l t Gland and Cloaca 1. Ion and f l u i d output. T o t a l yeq of Na +, K + and CI c o l l e c t e d from the s a l t gland and c l o a c a are presented i n Table I I I f o r each of the experime n t a l treatments. The o n l y s i g n i f i c a n t d i f f e r e n c e among the treatments was the amount o f CI e x c r e t e d v i a the c l o a c a ; the f i s h - f e d b i r d s e x c r e t e d l e s s than the o t h e r two groups. Approximately the same amount of Na + and CI were e x c r e t e d v i a the s a l t gland and c l o a c a ; most o f the K + was e x c r e t e d v i a the c l o a c a . The c a l c u l a t e d volume of water necessary f o r the ob-served e x t r a r e n a l s e c r e t i o n f o r a l l the b i r d s was 1.7 ml as compared to 8.0 ml o f f l u i d l o s t from the c l o a c a . 2. D i s t r i b u t i o n of i o n e x c r e t i o n . F i g u r e 6 i s a bar graph showing the r e l a t i v e percentage of the t o t a l e x c r e t i o n f o r each i o n and water from the s a l t gland, both c l o a c a l f r a c t i o n s , and the t o t a l c l o a c a l e x c r e t i o n . T h i r t y - e i g h t percent of the sodium, 6% of the potassium and 58% of the c h l o r i d e were e x c r e t e d v i a the s a l t gland. Only 15% of the water e x c r e t e d v i a these two routes was v i a the s a l t gland. C. Ion P a r t i t i o n i n g Between C l o a c a l F l u i d and S o l i d P o r t i o n s 25 TABLE I I I . Ion content o f s a l t gland s e c r e t i o n and c l o a c a l e x c r e t i o n c o l l e c t e d over 24 hours from Glaucous-winged G u l l s , Larus  glaucescens given e i t h e r f i s h , f i s h + s a l t , or s a l t only. The values are presented as means + SEM. T o t a l i o n content (yeq) S a l t gland C l o a c a l f l u i d C l o a c a l s o l i d C l o a c a l f l u i d & s o l i d S a l t Gland & c l o a c a l Na + f i s h ^ a only 648+280 284+ 86 324+ 55 608+112 1256+295 f i s h + s a l t b 642+252 766+538 305+ 88 997+531 1639+541 s a l t only 688+252 369+228 118+ 22 487+250 1175+ 25 K + f i s h only 93+ 55 462+105 807+142 1126+253 1361+182 f i s h + s a l t 58+ 20 597+270 645+178 1247+444 1305+449 s a l t only 71+ 46 '894+124 400+4.5 1294+120 1364+165 C l " f i s h f i s h only + s a l t d 927+408 763+288 255+169 .1009+688* 255+169 1009+668* 1153+417 s a l t only 775+275 1551+218* 1551+218* 2326+ 46 an=7, s a l t input was 3089+460 yeq Na + , 4703+700 yeq K +, 2619+ yeq C l . bn=4, s a l t input was 10740+152 yeq Na + , 4941+138 yeq K +, 10095+67 yeq C l ~ . cn=2. s a l t 'input was 3200 yeq Na +, 5000 yeq K +, 8200 yeq C l ~ . dn=2 * p<0.05, Mann Whitney U Test. Ion e x c r e t i o n from b i r d s fed only f i s h was compared to that o f the b i r d s fed f i s h + s a l t and independently to those fed s a l t only. 26 F i g u r e 6. The p a r t i t i o n i n g of ions and water i n 24 hour s a l t gland and c l o a c a l c o l l e c t i o n s from Glaucous-winged G u l l s , Larus glaucescens presented as percen-tages of t o t a l i o n and water e x c r e t i o n . E x c r e t i o n v i a the s a l t gland i s r e p r e s e n t e d by the s t r i p e d b a r s . C l o a c a l e x c r e t i o n i s d i v i d e d i n t o two p o r t i o n s ; f l u i d i s r e p r e s e n t e d by the white p o r t i o n of the bars and s o l i d i s represented by the s t r i p e d p o r t i o n of the b a r s . V e r t i c a l l i n e s r e p r e s e n t + 1 SEM. Sample s i z e was 11 f o r the sodium, potassium and water analyses and was 6 f o r the c h l o r i d e a n a l y s i s . SODIUM POTASSIUM CHLORIDE WATER 27 Only the cations were found i n both the f l u i d and s o l i d portions of the clo a c a l samples. Chloride was found only i n the f l u i d portion. Although the r e l a t i v e d i s t r i b u t i o n of Na + and K + be-tween the two portions varied, the so l i d s contained nearly h a l f of the t o t a l cations i n the cloacal excreta. The logarithims of the concentrations of sodium and potassium i n the f l u i d were plotted against the logarithim of t h e i r respective concen-trantions (yeq/g) i n the s o l i d portion (Figure 7a & 7b). There was no rel a t i o n s h i p between the two sodium concentrations but some ind i c a t i o n of a l i n e a r r e l a t i o n s h i p between the two potassium concentrations. The logarithim of the sum of the cations i n each f r a c t i o n was also plotted (Figure 7c) and a li n e a r r e l a t i o n s h i p was obtained. A s i g n i f i c a n t l y higher chloride concentration was observed i n the salt-only birds compared to the fish-only birds (Table IV). This was the only s i g n i f i c a n t difference i n ion concentrations i n the clo a c a l f l u i d . The weight of the clo a c a l s o l i d material excreted by the s a l t group was about 1/3 the weight excreted by the f i s h group. However, the amount of potassium per unit weight of s o l i d i s s i g n i f i c a n t l y greater i n the s a l t group compared to the f i s h group. For a l l regimes, more K + than Na + was found i n both the f l u i d and s o l i d portions; the Na +/K + r a t i o seemed to be higher i n the f l u i d than i n the s o l i d portion. gure 7. R e l a t i o n s h i p between c a t i o n c o n c e n t r a t i o n s i n the f l u i d p o r t i o n and s o l i d p o r t i o n of the c l o a c a l e x c r e t i o n . P l o t s (a) and (b) are the r e l a t i o n s h i p between Na + and K + r e s p e c t i v e l y i n the f l u i d and s o l i d p o r t i o n s . In (c) the sum o f Na + and K + i n each f r a c t i o n i s p l o t t e d . 28a FLUID NA • K (MEQ/L) 29 TABLE IV. Weight and ion concentration of f l u i d and s o l i d p ortions of c l o a c a l e x c r e t a c o l l e c t e d over 24 hours from Glaucous-winged G u l l s , Larus glaucescens given e i t h e r f i s h , f i s h + s a l t , o r s a l t o n l y . T h e values are presented as means + SEM. FLUID FRACTION Weight,g Ion Concentration, meg/ml Na +/ K Na T K+ C l " f i s h n=7 6.6 +0.7 42.7+13.1 68.1+13.3 37. 1+14.3 0.64+0.13 f i s h + n=4 s a l t 10.1 +4.2 50.8+20.6 56.6+ 8.7 55. 8+21.3 0.94+0.37 s a l t n=2 8.46+0.2 43.0+26.0 106 +17 184 * +37 0.46+0.32 SOLID FRACTION Weight,g Ion Content, yeq/g Na +/K + Na T K+ C l _ f i s h n=7 1.83+0.21 179 +30 439 +54 0 0.43+0.07 f i s h + n=4 s a l t 1.36+0.15 236 +83 524 +184 0 0.51+0.13 s a l t n=2 -• 0.45+0.05* 272 +76 903 +99* 0 0.30+0.05 *p < 0.05, Mann Whitney U Test Ion e x c r e t i o n from b i r d s fed only f i s h was compared to that o f the b i r d s fed f i s h + s a l t and independently to those fed s a l t only. 30 D. E v a p o r a t i v e Water Loss E v a p o r a t i v e water l o s s (EWL) was l e s s f o r the b i r d s given only s a l t than f o r the b i r d s t h a t r e c e i v e d f i s h or f i s h + s a l t . T h i s decrease i n EWL o c c u r r e d d e s p i t e somewhat h i g h e r ambient temperature and lower r e l a t i v e humidity (Table V), f a c t o r s which are expected to i n c r e a s e EWL. E. Comparison Between S a l t Gland S e c r e t o r s and Nonsecretors The i o n output f o r the s e c r e t o r s and n o n s e c r e t o r s i s presented i n Table VI. There are no s i g n i f i c a n t d i f f e r e n c e s i n the c l o a c a l i o n output f o r these two groups and s e c r e t i o n only i n c r e a s e d the t o t a l output of Na + and CI . S i m i l a r l y , t here were no s i g n i f i c a n t d i f f e r e n c e s i n the weights or concen-t r a t i o n s i n the f l u i d or s o l i d c l o a c a l f r a c t i o n s of the two groups (Table V I I ) . However, there was a tendency f o r the n o n s e c r e t o r s to have a s m a l l e r f l u i d and a g r e a t e r s o l i d por-t i o n than the s e c r e t o r s . The f l u i d i o n c o n c e n t r a t i o n s appear i d e n t i c a l f o r the two groups, but the nonsecretors seem to have l e s s i o n per gram s o l i d than the s e c r e t o r s . E v a p o r a t i v e water l o s s f o r the s e c r e t o r s was 57.8 + 8.2 ml and tended to be g r e a t e r than f o r the n o n s e c r e t o r s (39.1 + 2.2 ml), but t h i s d i f f e r e n c e was not s i g n i f i c a n t . 31 TABLE V. E v a p o r a t i v e water l o s s d u r i n g 24-hours from Glaucous-winged G u l l s , Larus glaucescens f ed f i s h , f i s h and s a l t or s a l t o n l y . Data values are means + SEM. EWL, g Temperature, °C R e l a t i v e Humidity F i s h 41.9+ 5. 6 22 + 0.6 72+0.9 n=7 F i s h & S a l t 58.0+11. 0 25 + 0.8 72+0.9 n=4 * S a l t 14.1+ 6. 8 28. 0+0.5 70+0.3 n=2 Ev a p o r a t i v e water l o s s c a l c u l a t e d by assuming EWL = AW, . , - (W. . , + W , . ) b i r d t o t a l s a l t c l o a c a l gland l o s s s e c r e t i o n p<0.05, Mann Whitney U Te s t Data from b i r d s f e d f i s h o n l y were compared to data from b i r d s f e d f i s h and s a l t and independently to those f e d s a l t o n l y . 32 TABLE VI. Ion content of s a l t gland and c l o a c a l i o n ex c r e t i o n : amount o f ion (peq) excreted per 24 hours by secreting 3- and nonsecreting Glaucous-winged G u l l s , Larus glaucescens. The values are means + SEM. K C l T o t a l ion content (yeq) S a l t Cloacal C l o a c a l C l o a c a l S a l t Gland gland f l u i d s s o l i d s F l u i d & S o l i d & c l o a c a l Na secretors n=6 1102+205 587+361 310+65 883+348 1985+274 nonsecretors n=5 98+ 41 263+106 326+ 61 589+131 687+190 secretors n=6 nonsecretors n=5 140+ 53 610+180 739+153 1352+266 7.8+3.8 392+105 759+153 1151+570 1434+254 1159+289 secretors n=5 1556+347" 561+292 nonsecretors 216+ 98 d 249+142d n=4 ~ 561+292 249+142' 1988+352' 318+222v p < 0.05; p < 0.005 (Mann Whitney U Test) a S e c r e t i n g g u l l s were defined as those that secreted at l e a s t 1 ml of f l u i d i n 24 hours. Three of the 7 b i r d s that received only f i s h were secretors and 3 of the 4 birds that received f i s h and s a l t s were secretors. b . n=4 c T n=3 n=2 33 TABLE VII. Weight and ion concentrations of f l u i d and s o l i d portions of c l o a c a l excreta c o l l e c t e d over 24 hours from s e c r e t i n g 3 and nonsecreting Glaucous-winged G u l l s , Larus glaucescens. FLUID FRACTION Weight,g Ion Concentration, meq/1 Na +/K + Na + K + C l " secretors 9.5 +2.8 48.0+13.5 63.0+ 7.7 41.1+ 9. 9 b 0 .83+0.24 n=6 nonsecretors 5.9+0.4 42.8+18.6 65.1+18.5 41.4+25. 8° 0 .71+0.2 3 n=5 SOLID FRACTION Weight,g Ion Per Unit Weight, yeq/g Na +/K + Na + K + C l ~ secretors 1.41+0.17 231 +60 545 +112 0 0 .47+0.16 n=6 nonsecretors 1.95+0.23 162 +18 382 +70 0 0 .45+0.06 n=5 Secreting g u l l s were defined as those that secreted at l e a s t 1 ml of f l u i d i n 24 hours. Three of the 7 birds that received only f i s h were secr e t o r s , and 3 of the 4 birds that received f i s h and s a l t were secr e t o r s . bn=5 Cn=4 34 IV. DISCUSSION A. T o t a l Body Water Volume and Turnover Rate TBW volume i s the same i n freshwater and seawater adapted g u l l s (Table I ) . T h i s o b s e r v a t i o n i s s u p p o r t i v e of the g u l l s ' a d a p t a t i o n t o c h r o n i c i n g e s t i o n o f h y p e r t o n i c f l u i d . The value o f TBW volume (79% body weight) ob t a i n e d i n t h i s study i s high compared t o those o f other b i r d s (Table I I , mean = 62% body weight) but l e s s than the 87.9% body weight o b t a i n e d f o r Glaucous-winged g u l l s by Ruch & Hughes (19 75). The l a r g e r TBW volume may be o f adaptive s i g n i f i c a n c e to marine b i r d s s i n c e a l a r g e r e l a t i v e f l u i d volume would b u f f e r the impact o f a s a l t l o a d on the s a l t c o n c e n t r a t i o n s of the body f l u i d s . (See Appendix III) [For example, 50 ml o f an 1000 m i l l i o s m o l a r s o l u t i o n (e.g., sea water) was c a l c u l a t e d (Appendix III) t o r a i s e the o s m o l a l i t y o f the body f l u i d s from 300 t o 401 mosm/1 i n an 800 gram b i r d i f the TBW volume i s 62% body weight. I f TBW volume i s 84% body weight, the same volume of sea water w i l l r a i s e the o s m o l a r i t y o f the body f l u i d s to 348 mosm/1.] S i m i l a r l y , the l a r g e TBW volume may pr o v i d e a r e s e r v o i r f o r p e r i o d s d u r i n g which water i s not a v a i l a b l e so t h a t a b i r d might be i n ne g a t i v e water balance f o r some time be f o r e i t s t i s s u e s become s e v e r e l y dehydrated. An example of the ad a p t i v e value o f a l a r g e t o t a l body water volume i s ob-served among the anuran amphibians. These organisms are h i g h l y 35 s u s c e p t a b l e to d e h y dration and have TBW volumes ranging from 77.5-80.1% body weight when normally hydrated (Thorson & S v i h l a , 1943). TBW volume measurements o f o t h e r c o a s t a l and p e l a g i c avian s p e c i e s would be of i n t e r e s t to determine i f l a r g e TBW volume i s a g e n e r a l phenomenon among b i r d s which l i v e i n a marine environment. Turnover r a t e o f water was the same i n f r e s h water and sea water adapted g u l l s . F l e t c h e r and Holmes (1968) r e p o r t decreased d r i n k i n g r a t e s i n ducks (Anas platyrhynchos) given 60% sea water as compared to ducks given f r e s h water. However, when the water i n t a k e s are converted to w e i g h t - r e l a t e d turnover r a t e s , the ^-^/2 v a l u e s a r e 4 - 2 a n < ^ 4 - 5 days f o r the freshwater and s a l i n e maintained b i r d s r e s p e c t i v e l y . The d i s c r e p a n c y i n d r i n k i n g r a t e s i s l o s t i n the turnover r a t e s due to lower body weights of s a l i n e - m a i n t a i n e d b i r d s and the assumption of a s l i g h t l y s m a l l e r t o t a l water volume as a percentage o f body weight f o r ducks i n accordance w i t h Ruch & Hughes (19 75) (Table II) . There are some s p e c i e s of p a s s e r i n e b i r d s t h a t t o l e r a t e d r i n k i n g s a l t water. D r i n k i n g r a t e s as a f u n c t i o n o f s a l t con-c e n t r a t i o n i n d r i n k i n g water have been measured f o r a number of s p e c i e s (Bartholomew & Cade, 1963; MacMillen & S n e l l i n g , 1966; Willoughby, 1968; McNabb, 1969; Poulson, 1969). Three types of response have been found: 1) an i n c r e a s e i n d r i n k i n g r a t e with i n c r e a s i n g s a l i n i t y u n t i l a c r i t i c a l maximum salini t y i s reached,rat which p o i n t d r i n k i n g r a t e f a l l s s h a r p l y (e.g., House F i n c h , Bobwhite); 2) no change i n d r i n k i n g r a t e with i n c r e a s i n g s a l i n i t y (e.g., C a l i f o r n i a Q u a i l , Gambel's Q u a i l ) ; and 3) a s l i g h t i n c r e a s e or no change from a very h i g h f r e s h water d r i n k i n g r a t e (e.g., Savannah Sparrow). I t appears t h a t those s p e c i e s l i v i n g i n the more s a l t s t r e s s e d environments ( C a l i f o r n i a Q u a i l , Gam-b e l ' s Q u a i l , and Savannah Sparrow) tend to have co n s t a n t d r i n k i n g r a t e s i n face of f l u c t u a t i o n s i n the s a l i n i t y of the d r i n k i n g water. D r i n k i n g r a t e s t u d i e s have a l s o been done with three s p e c i e s of g u l l . Harrimvan and Rare (1966) measured d r i n k i n g r a t e s of n i a i v e H e r r i n g G u l l s , Larus argentatus o f f e r e d d r i n k i n g s o l u t i o n s r anging i n c o n c e n t r a t i o n from d i s t i l l e d water to 1.0 M NaCl. The d r i n k i n g r a t e was constant f o r b i r d s o f f e r e d s o l u t i o n s from d i s t i l l e d water to about 0.2 M NaCl and then dropped to about 1/3 o f the o r i g i n a l d r i n k i n g r a t e as the s o l u t i o n s were i n c r e a s i n g l y c o n c e n t r a t e d . Harriman (1967) d i d a s i m i l a r experiment with young Laughing G u l l s , Larus a r t i c i l l a , a more p e l a g i c s p e c i e s than the H e r r i n g G u l l s . The b i r d s were not p r e v i o u s l y adapted to sea water and were randomly o f f e r e d d r i n k i n g s o l u t i o n s r anging i n c o n c e n t r a t i o n from d i s t i l l e d water t o 2.0 M NaCl. D r i n k i n g r a t e dropped on l y s l i g h t l y as the d r i n k i n g s o l u t i o n c o n c e n t r a t i o n i n c r e a s e d to 0.5 M NaCl which i s approximately e q u i v a l e n t to sea water con-c e n t r a t i o n s of these i o n s . The d r i n k i n g r a t e d i d d r o p . o f f ' r a p i d l y as the c o n c e n t r a t i o n of the s o l u t i o n s i n c r e a s e d from 0.5 to 1.0 M NaCl. The f a c t t h a t the d r i n k i n g r a t e o f the Laughing G u l l s remained constant through a more co n c e n t r a t e d 36A d r i n k i n g s o l u t i o n than t h a t o f the H e r r i n g G u l l s was i n t e r -p r e t e d by Harriman (1967) t o be due to the h a b i t a t d i f f e r e n c e of these two s p e c i e s . A t h i r d d r i n k i n g r a t e study with Larus  glaucescens, the same s p e c i e s used i n the present study, r e p o r t s t h a t a f t e r a d a p t a t i o n to sea water, the d r i n k i n g r a t e of g u l l s r e c e i v i n g f u l l s t r e n g t h sea water dropped to about h a l f o f the d r i n k i n g r a t e o f the same b i r d s w hile they were r e c e i v i n g tap water (Hughes, p e r s o n a l communication). The d r i n k i n g r a t e s i n Hughes' study were 0.098 ml/g body weight-day and 0.054 ml/g body weight-day when the g u l l s were d r i n k -i n g tap water and sea water r e s p e c t i v e l y . However, the TBW turn o v e r r a t e i n the presen t study was 0.064 ml/g weight-day under both d r i n k i n g regimes. These c o n t r a d i c t i o n s need to be e x p l a i n e d . Harriman (1967) has shown t h a t i t i s p o s s i b l e f o r at l e a s t one s p e c i e s o f g u l l , Larus a r t i c i l l a , t o have the same d r i n k i n g r a t e w h i l e d r i n k i n g NaCl s o l u t i o n s e q u i v a l e n t to sea water as w h i l e d r i n k i n g d i s t i l l e d water. However, d r i n k -i n g r a t e i n Glaucous-winged G u l l s (Hughes) appears to decrease by n e a r l y 50% when the b i r d s are d r i n k i n g sea water compared to when they are d r i n k i n g tap water. I t i s p o s s i b l e t h a t the g u l l s i n Hughes' study were o v e r - d r i n k i n g w h i l e on tap water or t h a t the turnover r a t e i n the presen t study i s a c t u a l l y a f u n c t i o n o f h a n d l i n g r a t h e r than the a c t u a l d r i n k i n g water composition. F u r t h e r experiments are needed to r e s o l v e t h i s apparent d i s c r e p a n c y . 36B Thus, i t appears i n neither pelagic g u l l s , ducks, nor probably i n s a l t adapted passerines, does the rate of water turnover change with drinking regime. Unlike the ducks, however, body, weight changes among the gulls were random with respect to drinking regime. This indicates that i n contrast to ducks, gulls are able to maintain weight and normal hydra-tion while drinking sea water. The rate of turnover i n gulls i s no d i f f e r e n t from water turnover rates i n other avian species (Figure 4). Therefore, t h i s aspect of water metabolism i s not modified i n t h i s species as a consequence of i t s a b i l i t y to ingest hypertonic s a l t solutions without becoming dehydrated. These data indicate that Glaucous-winged Gulls are highly adapted to withstand periods when only saline water i s available since they are able to maintain constant water flux even when ion flux increases. One may assume that there i s no continual accumulation of ions i n sea water maintained birds on the basis of plasma ion l e v e l s ; sodium levels are s l i g h t l y greater i n s a l t adapted birds as compared to fresh water birds (157 vs. 151 meq/1), but remain constant over time (Hughes, 1970). Since s a l t and water balance are c l o s e l y l i n k e d func-t i o n s the i n f l u x and e f f l u x o f both are c a r e f u l l y r e g u l a t e d . Water i n f l u x c o n s i s t s o f water drunk, water i n g e s t e d w i t h food, and met a b o l i c water. Water e f f l u x i n c l u d e s c l o a c a l water l o s s e s (mixed f e c a l and u r i n a r y ) , s a l t gland s e c r e t i o n , and e v a p o r a t i v e water l o s s e s . Since o v e r a l l water f l u x r e -mains const a n t , i t i s probable t h a t changes i n i o n e x c r e t i o n are achieved by r e d i s t r i b u t i o n o f e x c r e t e d ions and water between c l o a c a l and s a l t gland e x c r e t i o n s . T h e r e f o r e the volume and i o n c o n c e n t r a t i o n o f s a l t gland s e c r e t i o n and c l o a c a l e x c r e t a were measured over 24 hour i n t e r v a l s i n f r e s h and s a l t water adapted g u l l s . B. Ions and Water i n S a l t Gland S e c r e t i o n and C l o a c a l E x c r e t i o n There were very few s i g n i f i c a n t d i f f e r e n c e s among the experimental groups f o r the measured parameters. D i f f e r e n c e s t h a t may have e x i s t e d c o u l d have been obscured by s m a l l sample s i z e s and extremely l a r g e v a r i a n c e s w i t h i n groups. I n d i v i d u a l v a r i a t i o n i n c l o a c a l e x c r e t i o n among b i r d s i s g e n e r a l l y h i g h ; however, i n t h i s study there were a l s o s e v e r a l f a c t o r s i n the experimental d e s i g n t h a t c o n t r i b u t e d to the v a r i a n c e w i t h i n groups and decreased the d i f f e r e n c e s between groups. The most obvious c o n t r i b u t i o n to v a r i a n c e w i t h i n each group was the f o u r hour p e r i o d between f e e d i n g and be g i n n i n g of sample c o l l e c t i o n . During t h i s time, d r i n k i n g r a t e was not 38 c o n t r o l l e d or measured. D i f f e r e n c e s i n gut m o t i l i t y and d i g e s t i o n r a t e would have caused d i f f e r e n c e s i n e l e c t r o l y t e a b s o r p t i o n and e x c r e t i o n . Thus, a v a r y i n g p o r t i o n o f the i o n l o a d c o u l d have been e x c r e t e d d u r i n g the subsequent 24 hour study p e r i o d . Indeed,since 50% or more of an NaCl l o a d can be c o l l e c t e d from the s a l t gland w i t h i n 1 hour a f t e r l o a d i n g (Hughes, 19 70), i t i s probable t h a t much of the e x t r a r e n a l s e c r e t i o n immediately a s s o c i a t e d w i t h the f i s h meal o c c u r r e d d u r i n g t h i s 4 hour p e r i o d . Although s e c r e t i o n probably d i d occur b e f o r e c o l l e c t i o n began, i t i s important to note t h a t the i o n l o a d per b i r d expressed as yeq or yeq/100 g body weight v a r i e d w i t h i n each treatment s i n c e the f i s h weights and b i r d weights v a r i e d . Due to the l a c k of d i f f e r e n c e s between groups, the amounts of i o n or f l u i d l o s t from the two groups o f g u l l s t h a t were fed f i s h can be combined. T h e r e f o r e , subsequent d i s c u s s i o n w i l l c o n s i d e r the 11 f i s h - f e d g u l l s as a s i n g l e group. One o b j e c t i v e o f t h i s study was to q u a n t i f y the r o l e of the s a l t gland under c o n d i t i o n s i n which i o n e x c r e t i o n was not induced by a l a r g e s a l t l o a d . Of the t o t a l sodium and c h l o r i d e e x c r e t e d by the f i s h - f e d g u l l s 39% and 58% r e s p e c t i v e l y were removed by s a l t gland s e c r e t i o n (Figure 6) r e p r e s e n t i n g an extremely important f r a c t i o n of the t o t a l . Only 7% of the t o t a l potassium removed was s e c r e t e d by the s a l t gland which, although r e l a t i v e l y s m a l l , does r e p r e s e n t a c o n t r i b u t i o n to 39 potassium removal. Other i n v e s t i g a t o r s have obtained s i m i l a r r e s u l t s . Hughes (1972a) c o l l e c t e d spontaneous s e c r e t i o n s f o r 24 hours from Glaucous-winged G u l l s and the amounts o f sodium, potassium and c h l o r i d e s e c r e t e d were the same as i n t h i s study. C o n t i n u a l c l o a c a l e x c r e t i o n c o l l e c t e d from growing Terns (Hughes, 1968) and K i t t i w a k e s (Hughes, 1972b) consumming known amounts o f food both suggest t h a t an important f r a c t i o n o f the sodium e x c r e t i o n must be v i a the s a l t gland. The percentages of t o t a l sodium and c h l o r i d e e x c r e t i o n removed v i a the s a l t gland o f the g u l l s i n t h i s study are only s l i g h t l y d i f f e r e n t from percentages r e p o r t e d f o r s a l t loaded b i r d s f o r which c l o a c a l e x c r e t i o n and n a s a l s e c r e t i o n were c o l l e c t e d over a r e l a t i v e l y l o n g p e r i o d . Schmidt-Neilsen e t a l . (1958) r e p o r t e d t h a t 48%, 10% and 49% of the t o t a l sodium, potassium and c h l o r i d e r e s p e c t i v e l y e x c r e t e d i n 8 hours were removed v i a the s a l t gland i n a s a l t - l o a d e d cormo-r a n t (54 meq NaCl and 4 meq K + ) . Douglas (1970) c o l l e c t e d e x t r a r e n a l and c l o a c a l e x c r e t i o n s f o r 3-4 hours from p r e v i o u s l y f e d s a l t - l o a d e d H e r r i n g G u l l s , Larus argentatus, and found 66% of the sodium e x c r e t e d was s e c r e t e d by the s a l t gland. I f data from two l a b o r a t o r i e s (Holmes e_t a l , 19 6 8 and Hughes & Ruch, 1969) on spontaneous s a l t e x c r e t i o n from s a l i n e maintained ducks are combined, one can c a l c u l a t e t h a t 6 7.4% of the Na + e x c r e t e d and 0.75% of the K + e x c r e t e d o c c u r r e d v i a the s a l t gland. The low value f o r K + r e l a t i v e to oth e r s t u d i e s may be i n d i c a t i v e of the ducks' p l a n t d i e t s i n c e c l o a c a l values o f K + e x c r e t i o n were hig h r e l a t i v e to those f o r the g u l l s . 40 These re s u l t s for various marine birds are a l l very d i f f e r e n t from those obtained for fed Red-tailed Hawks, Buteo  jamaicensis (Johnson, 1969). Hav/ks do have s a l t glands, but during a 24 hour c o l l e c t i o n period only 3% of the t o t a l sodium excreted was contained i n the s a l t gland secretions. One can i n f e r from these data that i n contrast to the hawks, the g u l l s use the s a l t gland for routine Na + and CI excretion and some K + excretion as well as excretion subsequent to a s a l t load. The balance of the excreted ions were contained i n the clo a c a l samples, approximately 61% of the Na +, 45% of the CI , and 94% of the K + excreted by the birds i n t h i s study. A large portion of the measured cations was found with the pre-c i p i t a t e d s o l i d s . These ions do not contribute to the osmotic pressure of the cloacal f l u i d , and thus represent a reduction of cl o a c a l osmotic pressure roughly equivalent to 87 mosm/1. This important contribution to the t o t a l ion excretion i s r a r e l y considered although si m i l a r proportions of bound cations have been reported for Kittiwakes (Hughes, 1972b), Red-tailed Hawks (Johnson, 1969), and rooster (McNabb et a l . , 1973). In the two l a t t e r studies, NH* was measured i n the c l o a c a l excretion and found to be the major cation i n the f l u i d portion. This suggests that the bound Na + and K + i s an important means of allowing s u f f i c i e n t osmotic space i n the cl o a c a l f l u i d for nitrogen or acid excretion as ammonium. Hughes (19 72b) observed some chloride bound to the s o l i d portion. None was detected i n t h i s study, but t h i s i s 41 probably due to the d i l u t i o n of C l by the u r i c a c i d s o l u b i l i -z a t i o n procedure beyond the d e t e c t i o n l i m i t s of the c h l o r i d e method used r a t h e r than an a c t u a l absence o f c h l o r i d e . I t i s d i f f i c u l t to e v a l u a t e the e f f e c t of f e e d i n g on i o n e x c r e t i o n p a t t e r n s as only 2 b i r d s were not given a f i s h . The primary d i f f e r e n c e was a decrease i n the amount of s o l i d m a t e r i a l i n the c l o a c a l e x c r e t a (Table III) probably due to a decreased amount of s o l i d waste from the rectum. I f , how-ever, the fed b i r d s had more t o t a l u r i c a c i d and u r a t e excre-t i o n , t h e i r c a p a c i t y to b i n d c l o a c a l ions would be g r e a t e r than t h a t of u n f e d - b i r d s . Although not s i g n i f i c a n t , the group given o n l y s a l t d i d tend to have more i o n per u n i t weight of c l o a c a l s o l i d s . Potassium but not sodium a l s o tended to be more co n c e n t r a t e d i n the f l u i d p o r t i o n i n the 2 f a s t e d b i r d s than i n the f e d b i r d s and there i s a c o r r e l a t i o n between the t o t a l c a t i o n c o n c e n t r a t i o n i n the c l o a c a l f l u i d and the t o t a l c a t i o n s / u n i t weight o f s o l i d s (Figure 7). I t i s not p o s s i b l e to judge whether t h i s t r e n d toward h i g h e r i o n c o n c e n t r a t i o n s i s a r e s u l t of f a s t i n g or other circumstances i n t h i s study. A s i g n i f i c a n t d i f f e r e n c e was observed i n the c a l c u l a t e d e v a p o r a t i v e water l o s s among the 3 groups w i t h the unfed b i r d s b e i n g u n u s u a l l y low. Although these 2 b i r d s were s t u d i e d on the same day, which suggests an environmental f a c t o r , the mean temperature was h i g h e r and r e l a t i v e humidity was not s i g n i f i -c a n t l y d i f f e r e n t from those of other experimental days (Table 42 V)/.... The d i f f e r e n c e i n e v a p o r a t i v e r a t e must be r e l a t e d to a d i f f e r e n c e i n treatment or be an a r t i f a c t due to the s m a l l number of t r i a l s . There are a t l e a s t two h i g h l y s p e c u l a t i v e reasons why unfed b i r d s might have lower r a t e s o f e v a p o r a t i v e water l o s s . I t i s p o s s i b l e t h a t the unfed b i r d s were more dehydrated than the others as they were prevented access to water a f t e r r e c e i v i n g t h e i r s a l t l o a d whereas the ot h e r 2 groups were allowed 4 hours with d r i n k i n g water a v a i l a b l e . The g u l l s were observed to d r i n k a f t e r e a t i n g so i t i s l i k e l y t h a t these f i s h - f e d b i r d s d i d so. A second p o s s i b i l i t y i s t h a t the unfed b i r d s have a lower metabolic r a t e than the fed b i r d s and thus a lower r e s p i r a t o r y water l o s s . The c h l o r i d e c o n c e n t r a t i o n was s i g n i f i c a n t l y h i g h e r i n the f l u i d p o r t i o n o f the c l o a c a l e x c r e t i o n i n the unfed g u l l s . T h i s can be r e a d i l y e x p l a i n e d by the l a r g e r p r o p o r t i o n o f c h l o r i d e given i n these b i r d s ' s a l t l o a d compared to the f e d b i r d s (Table 113) . The b i r d s t h a t were f e d only f i s h r e c e i v e d an Na:Cl r a t i o o f 1:2, those t h a t were given f i s h and s a l t r e c e i v e d a r a t i o o f N a i C l o f 1-1 and the b i r d s given only a s a l t l o a d had an Na:Cl r a t i o of 0:39. The d i s c r e p a n c y came about because the e n t i r e anion l o a d a s s o c i a t e d w i t h both sodium and potassium was c h l o r i d e whereas the anion component o f the f i s h i n c l u d e d phosphate, b i c a r b o n a t e and a l a r g e v a r i e t y o f or g a n i c compounds. The a d d i t i o n a l s a l t l o a d given to the f i s h and s a l t group was comprised of NaCl. 43 U n f o r t u n a t e l y , due to the experimental p r o t o c o l , t h i s study does not r e a l l y t e s t the hypothesis t h a t the s a l t gland i s an important route f o r sodium and c h l o r i d e e l i m i n a t i o n un-der normal c o n d i t i o n s . The reason f o r t h i s i s t h a t the b i r d s were not given water d u r i n g the 24 hour c o l l e c t i o n p e r i o d , t h e r e f o r e , the experiments were designed to measure c l o a c a l e x c r e t i o n and s a l t gland s e c r e t i o n d u r i n g 24 hours of i n c r e a s -i n g d e h y d r a t i o n . T h i s i s a l s o an i n t e r e s t i n g q u e s t i o n as i t p e r t a i n s to the a b i l i t y o f marine b i r d s to s u r v i v e i n the absence of d r i n k i n g water. Nearly 40 ml of f r e e water was l o s t due to e v a p o r a t i o n d u r i n g the 2 4 hour c o l l e c t i o n p e r i o d which should have r a i s e d the o s m o l a l i t y of the body f l u i d s by about 6% (e.g., from 300 to 336 mosm/1). Thus, the extent of dehydration i n t h i s study cannot be c o n s i d e r e d t r i v i a l . The 24 hour water and i o n output from the g u l l s are compared wi t h those o f ducks t h a t were f a s t e d f o r 24 hours and s u b j e c t e d to a 33 hour c o l l e c t i o n of s a l t gland and c l o a -c a l e x c r e t i o n without water (Stewart, 1972) (Table V I I I ) . S ince Stewart r e p o r t e d o n l y data on b i r d s t h a t produced "measurable" s e c r e t i o n , data on the ' s e c r e t o r s ' from the p r e s e n t study are used f o r comparison. Ion output from the s a l t gland i s h i g h e r f o r NA + (75% vs. 57% of the t o t a l excreted) and lower f o r K + (2% vs. 9.5% of the t o t a l excreted) i n Stewart's as compared to the p r e s e n t study. The d i s c r e p a n c y i n the d i s t r i b u t i o n of sodium output i s probably due to a d i f f e r e n c e i n methodology s i n c e the c l o a c a l Na + output from the p r e s e n t study i n c l u d e d f l u i d and s o l i d c l o a c a l N a + whereas 44 TABLE V I I I . Comparison of 24 hour water and i o n output i n G u l l s , Larus glaucescens, and Ducks, Anas  p l a t y r h y n c h o s a . H 0, yl/lOOgBW Ion e x c r e t i o n , yeq/lOOg BW Na + K+ C l -G u l l s b ( s e c r e t o r s ) n=6 s a l t gland 359+ 71 133 +26 17+ 7 b 185+42 C c l o a c a 1100+281 100 +35 159+25 63+29 d e v a p o r a t i o n 6912+978 Ducks n=6 s a l t gland 283+ 76 162 +42 5+ 1 c l o a c a 2210+237 54.5+14.3 189+13 ev a p o r a t i o n 6200+380 Data converted from Table 2., Stewart (19 72). S e c r e t o r s were d e f i n e d as those t h a t s e c r e t e d a t l e a s t 1 ml of f l u i d . Stewart measured only f l u i d c l o a c a l i o n s . Indeed, when g u l l s a l t gland sodium output i s expressed i n terms of the c l o a c a l f l u i d N a + o n l y , the output from the s a l t gland i s 73%. Thus, g u l l s and ducks do appear to d i s t r i b u t e sodium i o n e x c r e t i o n s i m i l a r l y d u r i n g d e h y d r a t i o n . Moreover, the amount o f sodium e x c r e t e d v i a the s a l t gland i s a t l e a s t equal to and p o s s i b l y g r e a t e r than the amount e x c r e t e d v i a the c l o a c a i n both s p e c i e s . Other i n v e s t i g a t o r s r e p o r t decreases of 70-89% i n s a l t gland s e c r e t i o n volume i n dehydrated b i r d s compared to hydrated c o n t r o l s (Douglas & Neely, 1969; Ensor & P h i l l i p s , 19 72). However, i n both cases, the experiment was designed to measure s e c r e t i o n r a t e s i n response to a s a l t l o a d . Stewart (1972) and t h i s experimenter measured s e c r e t i o n r a t e i n r e -sponse to dehydration i t s e l f . These l a t t e r two s t u d i e s i n d i -cate t h a t s a l t gland s e c r e t i o n may be an important c o n t r i b u t i o n towards maintainence of osmotic homeostasis d u r i n g dehydration w h ile the former two s t u d i e s i n d i c a t e t h a t the c o n t r i b u t i o n of the s a l t gland may be l i m i t e d due to other c o n s t r a i n t s such as d i m i n i s h i n g f l u i d volumes. Thus, i t may be t h a t s a l t gland s e c r e t i o n d u r i n g dehydration may be a l i m i t e d emergency measure t h a t can a i d s u r v i v a l i n the s h o r t term o n l y . S e v e r a l m o d i f i c a t i o n s to the p r o t o c o l used i n t h i s study are necessary to q u a n t i f y the r o l e s of the s a l t gland, c l o a c a l f l u i d s and s o l i d s i n i o n e x c r e t i o n i n fed and normally hydrated c o n d i t i o n s . These are: p r o v i s i o n of water d u r i n g c o l l e c t i o n p e r i o d s , e l i m i n a t i o n of time between l o a d i n g and beginning sample c o l l e c t i o n , measurement of the volume of f l u i d s e c r e t i o n , and s c a l i n g of i o n l o a d i n g on a weight b a s i s . A y e t more complicated study i s necessary t o d i s t i n g u i s h among the s e v e r a l parameters t h a t d i r e c t l y determine c l o a c a l i o n and water e x c r e t i o n - - t h e kidney, the i n t e s t i n e and the c l o a c a i t s e l f . Crocker and Holmes (1971), Peaker e t al., (1968) and Skadhauge .(1967, 1976), have demonstrated the importance of the i n t e s t i n e and c l o a c a t o av i a n s a l t and water balance, but the a c t u a l con-t r i b u t i o n s o f these organs f o r f e d and hydrated marine b i r d s has not been q u a n t i f i e d . A f i n a l q u e s t i o n r a i s e d by t h i s study and o b s e r v a t i o n s by McNabb e t a l . , (1973) i s whether the r o l e of the c l o a c a l s o l i d s i n i o n e x c r e t i o n may be m o d i f i e d i n response t o s a l t l o a d i n g . McNabb e t a l . , (1973) found t h a t r o o s t e r s i n c r e a s e d t h e i r p r o t e i n u t i l i z a t i o n when given a s a l t l o a d , which suggests some i n t e r -dependence between s a l t and p r o t e i n metabolism and thus the ha n d l i n g of s a l t and d i e t . I t would be i n t e r e s t i n g t o pursue t h i s o b s e r v a t i o n by i n v e s t i g a t i n g whether marine b i r d s can vary the amount of bound ions i n response t o the needs f o r i o n excre-t i o n . For example, a change i n pH or the ammonium content of the u r i n e c o u l d change the p r e c i p i t a t i o n and b i n d i n g p r o p e r t i e s of the u r i c a c i d . C. Co n c l u s i o n s The r e s u l t s of these two experimental procedures p o i n t to s e v e r a l c o n c l u s i o n s r e g a r d i n g s a l t and water metabolism of Glaucous-winged G u l l s . These b i r d s have r e l a t i v e l y h i g h t o t a l body water volumes, but n e i t h e r the TBW volume nor the r a t e of TBW turnover change when the g u l l s are switched from a f r e s h -water to a seawater d r i n k i n g regime. Thus, these b i r d s are w e l l adapted t o v a r i a t i o n s i n the s a l i n i t y of t h e i r d r i n k i n g water. In c o n t r a s t , the g u l l s were unable t o e x c r e t e ions a t a r a t e e q u i v a l e n t t o water l o s s and remain i n s a l t and water balance d u r i n g a 2 4 hour dehydration p e r i o d . T h e r e f o r e , the mechanisms t h a t these b i r d s have t o m a i n t a i n normal f l u i d volumes and TBW turnover r a t e s w i t h i n c r e a s e d i o n uptake, are not able t o f u l l y compensate f o r a l a c k of water. Thus, the g u l l s are s p e c i f i c a l l y adapted to t h e i r environment of abundant water and e x c e s s i v e s a l t . The s a l t gland s e c r e t e d about h a l f of the t o t a l sodium and c h l o r i d e , and about 10% of the t o t a l potassium e x c r e t e d by the b i r d s i n t h i s study. T h i s d i s t r i b u t i o n of i o n e x c r e t i o n i s s i m i l a r t o those observed f o r e x t r a r e n a l i o n e x c r e t i o n i n response to a s a l t l o a d by o t h e r marine s p e c i e s . Thus, the s a l t gland does p l a y an important r o l e i n i o n e x c r e t i o n f o r these b i r d s i n f e d but dehydrated c o n d i t i o n s . Since the a b i l i t y of the s a l t gland to f u n c t i o n appears to decrease with i n c r e a s i n g d e h y d r a t i o n , i t i s l i k e l y t h a t normally fed and normally hydrated b i r d s a l s o use the s a l t gland as a route f o r i o n e x c r e t i o n . The c l o a c a l s o l i d s a l s o p l a y a r o l e i n i o n e x c r e t i o n i n a d d i t i o n t o t h e i r well-known r o l e of removing nitrogenous wastes without c o n t r i b u t i n g t o the osmotic pressure of the u r i n e . C a t i o n s p r e c i p i t a t e d w i t h the c l o a c a l s o l i d s ranged 48 roughly from a fourth to a half of the t o t a l output of sodium and potassium. This important but often neglected f r a c t i o n should be included i n any s a l t balance studies for u r i c o t e l i c species. The e f f e c t of feeding on the patterns of s a l t and water excretion i s s t i l l ambiguous but i t c l e a r l y has some ef f e c t . No d e f i n i t e conclusions may be drawn from t h i s study but 2 possible areas for s p e c i f i c research are i d e n t i f i e d ; 1) characterization of u r i c acid/ion associating c o l l o i d excretion patterns i n terms of feeding and protein content of the d i e t , and, 2) comparison of evaporative water loss rates and metabolic rates between fed and starved b i r d s . The over-riding conclusion that may be drawn from these experiments and discussion i s that although the s a l t gland i s the primary adaptation for s a l t excretion, i t i s only one of several coordinated adaptations i n the water and s a l t metabolism of marine avian species. Other, more subtle, as-pects of s a l t and water metabolism have been suggested and need to be explored and quantified i n order to f u l l y understand the osmoregulatory processes i n these birds. 49 V. SUMMARY Two aspects of osmoregulatory physiology were charac-ter i z e d for Glaucous-winged Gulls, a representative marine avian species, i n order to i d e n t i f y s p e c i f i c adaptations to th e i r marine environment and to describe the integration of several means of ion excretion i n fed b i r d s . Two indices of o v e r a l l water metabolism, TBW volume and turnover rate,were compared i n gulls adapted to drinking fresh water and then to drinking sea water to determine i f o v e r a l l water metabolism was affected by prolonged ingestion of sea water. These values were also compared to those for other avian species by allometric equations to see i f the gulls were unique with respect to these two parameters. Turnover rate, measured by THO loss, was no d i f f e r e n t i n sea water adapted and fresh water adapted g u l l s , nor was there a difference between gulls and other birds. The volume of TBW was computed from i n i t i a l THO space and there was no change with drinking regime. However, the size of the TBW space was unusually high, equalling 79% of body weight compared to a mean of 62% for other birds. Two advantages accruing from a larger r e l a t i v e TBW space may be: 1) reducing the change i n osmotic pressure due to ingestion of hypertonic solutions, and 2) allowing a greater degree of des-s i c a t i o n before tissues become irreparably damaged due to dehydration. 50 A second s e t of experiments was designed t o q u a n t i f y the e x c r e t i o n p a t t e r n f o r sodium, potassium and c h l o r i d e ions when these are i n g e s t e d w i t h a f i s h , a normal d i e t a r y com-ponent f o r the g u l l s . The f i s h was s l i g h t l y hyperosmotic t o the body f l u i d s o f the b i r d s and con t a i n e d a n i t r o g e n l o a d u n l i k e the hyperosmotic i o n loads u s u a l l y given to study s a l t e x c r e t i o n , i o n e x c r e t i o n s from the s a l t gland and the c l o a c a were c o l l e c t e d f o r 24 hours b e g i n n i n g 4 hours a f t e r f e e d i n g . Sodium and c h l o r i d e , the dominant ions i n the s a l t gland s e c r e t i o n , were e x c r e t e d v i a both routes i n roughly equal amounts whereas most o f the potassium was e x c r e t e d v i a the c l o a c a . T h i s a t t e s t s to the f u n c t i o n a l importance of the s a l t gland i n circumstances which do not i n v o l v e acute and h y p e r t o n i c i o n l o a d i n g . U n f o r t u n a t e l y , the r e s u l t s are com-promised by the f a c t t h a t the b i r d s were allowed to dehydrate d u r i n g i o n c o l l e c t i o n and i t i s not p o s s i b l e t o s t a t e i f or how t h i s a f f e c t e d the s a l t gland f u n c t i o n . Ions from the c l o a c a were e x c r e t e d i n two f o r m s — d i s s o l v e d i n the c l o a c a l f l u i d or bound to the s o l i d urates and mucous. In t h i s study, s i g n i f i c a n t p o r t i o n s o f the Na + + and K e x c r e t e d were measured i n both f r a c t i o n s (43% of c l o a c a l N a + and 61% of c l o a c a l K + were i n the s o l i d p o r t i o n ) ; CI was not d e t e c t e d i n the s o l i d p o r t i o n but t h i s absence was probably a f u n c t i o n o f the a n a l y s i s used. Two b i r d s were gi v e n the i o n l o a d a s s s o c i a t e d w i t h e a t i n g a f i s h but not the n i t r o g e n l o a d . 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The e x c r e t i o n of urat e and c a t i o n i c e l e c t r o l y t e s by the kidney o f the male Domestic Fowl (Gallus domesti- cus) . J . Comp. P h y s i o l . 82:47-57. 29. Ohmart, R. D., T. E. Chapman, and L. Z. McFarland. 1970. Water turnover i n Roadrunners under d i f f e r e n t e n v i r o n -mental c o n d i t i o n s . Auk 87:787-793. 30. Poulson, T. L. 1969. S a l t and water balance i n Seaside and S h a r p t a i l e d Sparrows. Auk 86:473-489. 31. Ruch, F. E., J r . and M. R. Hughes. 19 75. The e f f e c t s of h y p e r t o n i c sodium c h l o r i d e i n j e c t i o n on body water d i s t r i b u t i o n i n ducks (Anas p l a t y r h y n c h o s ) , g u l l s (Larus glaucescens) and r o o s t e r s (Gallus domesticus). Comp. Biochem. and P h y s i o l . 52A:21-28. 32. Schmidt-Neilsen, K., C. B. Jorgensen, and H. Osaki . 195 8. E x t r a r e n a l s a l t e x c r e t i o n i n b i r d s . Am. J . P h y s i o l . 193:101-107. 33. S i e g e l , S. 1956. Nonparametric S t a t i s t i c s f o r the B e h a v i o r a l S c i e n c e s . McGraw H i l l Book Co., N. Y. 34. Skadhauge, E. 1967. In v i v o p e r f u s i o n s t u d i e s o f the c l o a c a l water and e l e c t r o l y t e r e s o r p t i o n i n the Fowl (Gal l u s domesticus). Comp. Biochem.and P h y s i o l . 23:483-501. 35. Skadhauge, E. 1976. C l o a c a l a b s o r p t i o n of u r i n e i n b i r d s . Comp. Biochem. and P h y s i o l . 55A:93-98. 36. Skadhauge, E. and S. D. Bradshaw. 1974. S a l i n e d r i n k -i n g and c l o a c a l e x c r e t i o n o f s a l t and water i n the Zebra F i n c h . Am. J . P h y s i o l . 227:126 3-1267. 55 37. Smyth, M. and G. A. Bartholomew. 1966. The water economy o f the B l a c k - t h r o a t e d Sparrow and the Rock Wren. Condor 68:447-458. 38. Stewart, D. J . 1972. S e c r e t i o n by s a l t gland d u r i n g water d e p r i v a t i o n by the duck. Am. J . P h y s i o l . 223:384-386. 39. Stewart, D. J . , W. N. Holmes, and G. F l e t c h e r . 1969. The r e n a l e x c r e t i o n o f nitrogenous compounds by the duck (Anas platyhynchos) maintained on freshwater and on h y p e r t o n i c s a l i n e . J . Exp. B i o l . 50:527-539. 40. Thomas, D. H. and J . G. P h i l l i p s . 1975. S t u d i e s i n a v i a n a d r e n a l s t e r i o d f u n c t i o n . I I . Chr o n i c adrena-lectomy and the turnover o f 3(H)20 i n Domestic Ducks (Anas p l a t y r y n c h o s L.) Gen. Comp. E n d o c r i n o l . 26:404-411. 41. Thorson, T. B. and A. S v i h l a . 1943. C o r r e l a t i o n o f the h a b i t s of amphibians w i t h t h e i r a b i l i t y to s u r v i v e the l o s s o f body water. Ecology 24:374-381. 42. Willoughby, E. J . 1966. Water requirements o f the Ground Dove. Condor 68:243-248. 43. Willoughby, E. J . 196 8. Water economy o f the Stark's Lark and Grey-backed F i n c h Lark from Namib d e s e r t of South West A f r i c a . Compl Biochem. P h y s i o l . 27:723-745. 56 A P P E N D I X I C O M P U T E R P R O G R A M CALL P I 1 3 0 IN=5 10=6 READ ( IN, lO) NB 10 FORMAT (13) N = N13*9 DO 5 J = l , NB WRITE (10, 100) J l O O FORMAT (1H1, 12X, 'B IRD #' , 1 3 . / / 1 2 X , ' T I M E ' . 10X. ' B ' , 8X. ' D P M ' , S X , 1 ' M C I / M L ' , 4X-, 'TRUE M C I / M L ' , 6 X , ' L O G M C I / M L ' / / ) CALL SCALF (0. 5, 1. 0. O. , - 6 . ) CALL FGRID (0, 0, - 6 . . 1. , 14) CALL FORID (1. 0, - 6 . • 1. . 5) DO 25 IX=1,2 SY = 0. ST = 0. STY = 0. STS = 0. C = 0 X = 1. DO 15 I — 1,9 READ ( IN, 30) XT 30 FORMAT (F5. 2) READ ( IN, 50) B 50 FORMAT (F7. 0) 2 EF = . 256 4 DPM = B / E F XC = DPM/2. 2E3 IF ( 1 -2 ) 13, 17. 19 13 T=XT BG=XC GO TO 13 17 B T - X T 19 T = ( (X-2 . ) *43 ( B T - X T ) ) / 2 4 . 18 CONTINUE XM = XC-BG IF (XM) '21, 21, 24 21 Y=l. C=C+1. GO TO 23 24 Y = ALOGIO(XM) NY =Y IF (NY-1) 41 , 42, 41 57 42 41 C = C + 1. GO TO 23 SY = SY + Y STY = STY + T#Y ST = ST + T STS = STS + T * T 33 C A L L FPLOT ( -2 , T. C A L L POINT ( IX -1 ) C A L L PENUP Y) 28 200 WRITE (10. 200) T» FORMAT ( I U . F5. 2, X=X+1. B, DPM, XC, XM, Y F12. 0, F l l . 0. E14. 3, E14. 3. F12. 5) IS CONTINUE XK = < S T Y - S Y * S T / ( 9 . A = < S Y - X K * S T ) / ( 9 . • Y14 = XK*14. + A - C ) ) / ( S T S - S T * S T / ( 9 . - C ) ) -C ) • T5 = - . 693 /XK IF <A . OT. O. . OR. C A L L FPLOT (0, 0. ," A . LT. - 6 . . OR. Y14 . GT. A) O. ) GO TO 61 IF <Y14 . LT. - 6 . ) i X=14. Y=Y14 GO TO 201 201 GO TO 202 Y=-6. X=<A+6. ) /XK 202 61 CALL FPLOT (2, X. Y) CALL FPLOT ( 1, 20. . - 6 . ) WRITE (10, 300) XK, T5 300 25 FORMAT ( / / 12X, ' K IF <J . EO. 5) GO CONTINUE = F6. 3. / 1 2 X , ' T ( 1/2) = ' TO 5 F6. 3, / / / / / / ) 5 CONTINUE STOP END 58 APPENDIX I I DATA FROM INDIVIDUAL BIRDS FOR ION AND FLUID EXCRETION DURING A 24 HOUR COLLECTION PERIOD. Table 1. Ion lo a d , r e n a l and e x t r a r e n a l i o n e x c r e t i o n f o r i n d i v i d u a l b i r d s d u r i n g a 24 hour c o l l e c -t i o n p e r i o d . Table 2. Weight l o s s e s and c a l c u l a t e d e v a p o r a t i v e water l o s s f o r i n d i v i d u a l Glaucous-winged G u l l s d u r i n g 24 hours. Table 3. Co n c e n t r a t i o n s of ions i n c l o a c a l f l u i d s and amount of i o n per u n i t weight o f c l o a c a l s o l i d s f o r i n d i v i d u a l g u l l s d u r i n g 24 hour c o l l e c t i o n p e r i o d . TABLE 1. Ion load, renal and extrarenal ion excretion for individual birds during a 24 hour collection period. SALT CAPSULE FISH • SALT CAPSULE • DIST. HjO 8 9 . 10 11 12 13 INPUT g fish Na+ (ueq) K+_(Ueq) Cl~ (ueq) 64 3232 4922 2739 70.5 3560 5422 3017 42.2 2131 3245 1806 63.2 3192 4860 2705 107.2 5414 8244 4588 35.5 1793 2730 1519 45.5 2298 3499 1947 62 10591 4768 10114 65 11133 499? 10032 69 10805 5306 10273 61 10431 4691 9961 3200 5000 8200 3200 . 5000 8200 OUTPUT SALT GLAND Na+ (ueq) K* (ueq) CI" (Ueq) CLOACAL FLUID N a * Ueq) K (ueq) CI" (ueq) CLOACAL SOLIDS Na+ (v,cq) (ueq) total ueq K* (ueq) (ueq) total ueq CI" No or trace amounts of chloride were found in a l l cloacal solids' samples. 38 1683 1613 8 35 36 278 48 1300 494 683 92 4.0 395 159 63 1.0 24 2.0 105 50 70 8 2S 2050 2250 875 25 338 1050 475 83 276 272 456 95 701 104 349 2363 21 332 413 410 237 861 367 817 127 693 1320 139 235 93 290 89 •410 51 739 114 309 1709 435 50 235 260 200 270 185 55 225 355 . 50 97 39 122 104 26 165 81 100 299 16 121 532 89 357 364 226 435 266 155 S24 371 171 740 315 875 310 565 870 140 360 475 415 245 150 93 401 194 161 464 364 341 650 16 97 890 413 1276 504 726 1334 504 701 1125 431 342 463 25 1050 596 770 1322 135 5 140 400 4 404 913 116 500 141 1018 1780 70 26 96 360 35 395 TOTAL CLOACAL Na+ (ueq) 615 365 629 820 321 1136 K* (ueq) 1303 823 1513 1365 1093 2151 Cl~ Totals are as listed under cloacal fluid. 370 631 504 1394 2588 2445 392 570 503 577 736 1174 237 1413 TOTAL OUTPUT Na+ (ueq) K+ (ueq) CI* (ueq) 653 2053 1307 1218 118 2340 2242 1672 2339 1655 1428 1285 357 1094 76 1414 2175 761 418 633 1804 1499 3082 2495 1075 640 595 585 1199 1199 2372 1150 1529 2280 TABLE 2. Weight losses and calculated evaporative water loss for individual Glaucous-winged Gulls during 24 hours. •1 2 3 4 5 6 7 8 9 10 11 12 13 Body weight wt (g) 760 832 843 764 850 870 914 770 965 936 790 839 756 wf (g) 708 745 790 704 797 813 870 683 890 874 744 803 733 W (g) 52 87 47 60 S3 57 44 87 75 62 46 36 23 Salt aland ml H 20 a .078 4.47 4.58 2.06 0.75 0.74 0.13 3.47 1.32 1.99 .638 1.74 1.76 Cloacal fluid g 6.6 9.2 4.9 9.2 5.1 6.2 5.0 8.9 22.1 2.6 6.7 8.64 8.28 Cloacal solids g 2.72 1.16 2.06 1.12 1.84 2.06 1.32 1.24 1.09 1.80 1.29 .40 .49 g solids g fluids .412 .126 .420 .122 .361 .332 .36 3 .139 .049 .690 .192 .047 .055 Evap. 820° g 42.4 72.5 35.0 47.6 45.3 48.0 37.6 73.4 50.5 55.6 37.3 25.2 12.5 'Calculated using measured ion output and assuming ion concentrations equal to those measured for spontaneous secretion (Hughes, 1971a). 'calculated by assuming that a l l unaccounted for weight loss was due to evaporative water loss. CTl O TABLE 3. Concentrations of ions in cloacal fluids and amount of ion per unit weight of cloacal solids for individual gulls during 24 hour collection period. 1 2 3 4 5 6 7 8 9 10 11 12 13 C l o a c a l f l u i d N a + roeq/1 12. ,5 30. 0 55.0 49.5 18.5 112. 5 21.0 39.0 106.5 8.0 49.5 69.0 17.0 K+ neq/1 62. .5 44. 5 48.0 93.5 71.5 131. 0 25.S 77.5 59.5 54.5 35.0 89.0 123.0 C l " meq/1 14. .0 31. 5 18.0 44.5 10.0 118. 5 23.0 34.5 77.0 — ~ 153 215 N a / K .200 675 1.14 .530 .254 850 .825 .505 1.69 .142 1.41 .775 .138 C l o a c a l s o l i d s N a + yeq/1 196 76. 7 174 324 123 211 146 125 479 207 133 347 196 K+ ueq/1 328 356 620 449 394 648 277 567 1029 240 265 1002 804 N a / K .598 215 .280 .722 .311 326 .527 .221 .466 .861 .500 .347 .243 62 APPENDIX I I I EFFECTS OF TBW VOLUME ON THE ESTIMATED OSMOTIC EFFECTS OF A HYPERTONIC SALT LOAD. Table 1. Estimated change i n o s m o l a l i t y o f the body f l u i d s o f a g u l l due to a s a l t l o a d f o r two TBW volumes. 63 I t i s observed t h a t Glaucous-winged G u l l s have a TBW volume o f 80-88% W (Table II) whereas mean TBW volume f o r other s p e c i e s i s 62% W. Could t h i s a p p a r e n t l y l a r g e r TBW volume p l a y a r o l e i n b u f f e r i n g the osmotic e f f e c t s o f a hy p e r t o n i c l o a d , such as the i n g e s t i o n o f sea water? An answer can be p r o v i d e d by the f o l l o w i n g thought experiment. Assume 50 ml of sea water 1000 mosm/1 are given to an 800 g g u l l w i t h body f l u i d o s m o l a l i t y o f 300 mosm/1. I f the sea water o s m o t i c a l l y e q u i l i b r a t e s w i t h the e n t i r e TBW volume, what i s the i n c r e a s e i n body f l u i d o s m o l a l i t y i f the TBW volume i s 62% W? 84% W? I f the time course o f s e c r e t i o n i s such t h a t the sea water o s m o t i c a l l y e q u i l i b r a t e s w i t h the e x t r a c e l l u l a r f l u i d space (ECF) o n l y , the c a l c u l a t i o n o f the i n c r e a s e i n body f l u i d o s m o l a l i t y can s t i l l be done u s i n g Ruch and Hughes' (1975) estimate o f ECF as 44% TBW volume. The r e s u l t s o f such c a l c u l a t i o n s are presented i n Table I. The o s m o l a l i t y o f the body f l u i d i n c r e a s e s f o r both values o f TBW volume but the b i r d w i t h the l a r g e r TBW volume experiences 16-29 mosm/1 l e s s i n c r e a s e . TABLE 1. Estimated change i n the o s m o l a l i t y of the body f l u i d s o f a g u l l due t o a s a l t l o a d f o r two TBW volumes. Change i n o s m o l a l i t y o f the body f l u i d s A mosm. Load e q u i l i b r a t e d TBW wolume, % W wit h : 62% 84% TBW +64 + 4 8 ECF +130 +101 i n i t i a l plasma o s m o l a l i t y = 300 mosm/1 lo a d = 50 ml of 1000 mosm/1 sea water W = 800 g 

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