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An investigation of rodents' use of learned caloric information in diet selection and foraging Arbour, Katherine Johanna 1987

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INVESTIGATION OF RODENTS' USE OF LEARNED CALORIC INFORMATION IN DIET SELECTION AND FORAGING by KATHERINE J . ARBOUR B.A., S t a t e U n i v e r s i t y Of New York At P l a t t s b u r g h , 1 9 8 4 A THESIS SUBMITTED IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF ARTS in THE FACULTY OF GRADUATE STUDIES Department Of Psychology 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 A p r i l 1 9 8 7 © Katherine J . Arbour, 1 9 8 7 In presenting th i s thesis in p a r t i a l fu l f i lment of the requirements for an advanced degree at the Univers i ty of B r i t i s h Columbia, I agree that the L i b r a r y s h a l l make i t f ree ly ava i lab le for reference and study. I further agree that permission for extensive copying of th i s thesis for scho lar ly purposes may be granted by the Head of my Department or by his or her representat ives . It i s understood that copying or publ i ca t ion of th is thesis for f i n a n c i a l gain s h a l l not be allowed without my written permission. Department of Psychology The Univers i ty of B r i t i s h Columbia 2075 Wesbrook Place Vancouver, Canada V6T 1W5 Date: A p r i l 15, 1987 i i A b s t r a c t When given a c h o i c e between two foods of equal c a l o r i c value but d i f f e r e n t f l a v o r s , r a t s show a robust preference f o r that food whose f l a v o r was p r e v i o u s l y a s s o c i a t e d with a higher c a l o r i e food. T h i s f i n d i n g suggests that rodents may i d e n t i f y food q u a l i t y by sensory s i g n a l s such as t a s t e . The f i r s t p o r t i o n of t h i s t h e s i s e x p l o r e s t h i s f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t i n other rodents, namely hamsters and g e r b i l s . When hamsters were t e s t e d i n the same paradigm as r a t s , the c o n d i t i o n i n g e f f e c t was not observed. T h i s discrepancy may have r e s u l t e d from the hamsters' a b i l i t y to s t o r e food mash i n t h e i r cheekpouches. A c c o r d i n g l y , hamsters were next presented with l i q u i d d i e t s which c o u l d not be cheekpouched. The c o n d i t i o n i n g e f f e c t was observed when d i f f e r e n t f l a v o r s were a s s o c i a t e d with d i f f e r e n t q u a l i t y l i q u i d d i e t s . However, the e f f e c t was l e s s robust than that d i s c o v e r e d f o r r a t s . A second s p e c i e s , g e r b i l s , d i d show robust c o n d i t i o n i n g e f f e c t s . Thus, u n l i k e r a t s and g e r b i l s who show a robust f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t , hamsters are l e s s l i k e l y to i d e n t i f y food q u a l i t y by using t a s t e cues. Once c o n d i t i o n e d to detect c a l o r i c d e n s i t y by using f l a v o r cues, hamsters and g e r b i l s were placed on an 8-arm r a d i a l maze that c o n s i s t e d of four arms b a i t e d with h i g h - c a l o r i e l i q u i d and four arms b a i t e d with l o w - c a l o r i e l i q u i d . The purpose of t h i s second, p a r t of the t h e s i s r e s e a r c h was to i n v e s t i g a t e the rodents' p r e f e r e n c e f o r food l o c a t i o n s that contained food of v a r y i n g q u a l i t i e s . Both s p e c i e s were expected to v i s i t and d r i n k f i r s t from the arm l o c a t i o n s c o n t a i n i n g the higher c a l o r i e l i q u i d . Although hamsters d i d not v i s i t more h i g h - c a l o r i e arm l o c a t i o n s , they d i d d r i n k from these arms more o f t e n . When v i s i t i n g arm l o c a t i o n s , hamsters appeared to use a c i r c l i n g s t r a t e g y that began i n the same arm each t r i a l and c o n s i s t e d of v i s i t s to c o n s e c u t i v e arms. G e r b i l s n e i t h e r v i s i t e d nor drank more o f t e n from the h i g h - c a l o r i e arm l o c a t i o n s . G e r b i l s a l s o d i d not appear to use a c i r c l i n g s t r a t e g y . Thus, when fo r a g i n g on an 8-arm r a d i a l maze fo r food of v a r y i n g q u a l i t y , hamsters' use of a c i r c l i n g s t r a t e g y p r o h i b i t e d them from f i r s t v i s i t i n g h i g h - c a l o r i e arms but not from p r e f e r e n t i a l l y d r i n k i n g from these l o c a t i o n s . U n l i k e hamsters, g e r b i l s d i d not adopt a s t r a t e g y to c o l l e c t food rewards and were not s e l e c t i v e about the food reward that was consumed. The f o r a g i n g s t r a t e g i e s of hamsters was f u r t h e r explored i n the t h i r d part of the t h e s i s . Hamsters were allowed to forage on an e q u a l l y - b a i t e d 17-arm r a d i a l maze. Each arm l o c a t i o n was b a i t e d with a sunflower seed. Once again , hamsters v i s i t e d arm l o c a t i o n s by using a c i r c l i n g s t r a t e g y which c o n s i s t e d of v i s i t s to c o n s e c u t i v e arms. However, on the l a r g e r maze hamsters d i d not begin each t r i a l i n the same arm l o c a t i o n . In a d d i t i o n , hamsters that were pl a c e d on the same maze with 4 of the 17 b a i t e d arms blocked, given 13 arm l o c a t i o n c h o i c e s , removed from the maze while the blocks were a l s o removed, and pl a c e d back on the maze to s e l e c t 4 a d d i t i o n a l arm l o c a t i o n s , d i d not p r e f e r e n t i a l l y s e l e c t the p r e v i o u s l y blocked arms. Thus, hamsters whose response a l g o r i t h m was d i s r u p t e d d i d not show a i v memory-based s t r a t e g y f o r c o l l e c t i n g s e e d s f r o m t h e maze. The major c o n c l u s i o n s f r o m t h i s r e s e a r c h a r e t h a t 1.) Hamsters c a n l e a r n t o a s s o c i a t e c a l o r i c d e n s i t y and f l a v o r c u e s , b u t t h e l e a r n e d e f f e c t i s e a s i l y e x t i n g u i s h e d . 2.) T h i s d i e t a r y i n f o r m a t i o n may be u s e d when d e c i d i n g what t o e a t but not where t o f o r a g e . 3.) H a m s t e r s a p p e a r t o be h a r v e s t e r s who v i s i t a l l f o r a g i n g l o c a t i o n s by a d o p t i n g a r e s p o n s e s t r a t e g y . 4.) G e r b i l s c a n a l s o l e a r n t o a s s o c i a t e c a l o r i c d e n s i t y and f l a v o r , and t h e l e a r n e d e f f e c t i s r o b u s t . 5.) G e r b i l s do n o t a p p e a r t o use t h i s i n f o r m a t i o n when d e c i d i n g w h i c h f o o d s t o e a t o r where t o f o r a g e . I t w i l l be i n t e r e s t i n g f o r f u t u r e s t u d i e s t o see i f r a t s use f l a v o r - c a l o r i e i n f o r m a t i o n i n f o r a g i n g s e t t i n g s . V Table of Contents A b s t r a c t i i L i s t of F i g u r e s v i Acknowledgement ix Chapter I INTRODUCTION 1 Chapter II EXPERIMENT 1 14 1 . PART 1 14 1 .1 Method 14 1.1.1 Subjects 14 1.1.2 M a t e r i a l s 15 1.1.3 Procedure 16 1.1.4 S t a t i s t i c s 17 1.1.5 R e s u l t s And D i s c u s s i o n 18 2. PART 2 21 2.1 Method 22 2.1.1 Subjects 22 2.1.2 M a t e r i a l s 22 2.1.3 Procedure 23 2.1.4 S t a t i s t i c s 24 2.1.5 R e s u l t s And D i s c u s s i o n 25 3. PART 3 32 3.1 Method 33 3.1.1 Subjects 33 3.1.2 M a t e r i a l s 33 3.1.3 Procedure 33 3.1.4 S t a t i s t i c s 34 3.1.5 R e s u l t s And D i s c u s s i o n 34 Chapter III EXPERIMENT 2 45 4.1 Method 45 4.1.1 Subjects 45 4.1.2 M a t e r i a l s 45 4.1.3 Procedure 46 4.1.4 S t a t i s t i c s 47 4.1.5 R e s u l t s And D i s c u s s i o n ...49 Chapter IV EXPERIMENT 3 58 5.1 Method 58 5.1.1.Subjects 58 5.1.2 M a t e r i a l s 59 5.1.3 Procedure 59 5.1.4 S t a t i s t i c s 60 5.1.5 R e s u l t s And D i s c u s s i o n 61 v i Chapter V GENERAL DISCUSSION 77 References 89 v i i L i s t of Figures 1. Mean consumption of i s o c a l o r i c mash whose f lavors were previous ly paired with a high- or low-ca lor ie mash by hamsters af ter 1 hr and 24 hr 19 2. Mean consumption of h igh- and low-ca lor ie Sustacal l i q u i d by hamsters during the condi t ioning and test phases 26 3. Mean consumption of i s o c a l o r i c l i q u i d associated with a f lavor previously paired to high- or low-calor ie Sustacal by hamsters in the test phase 28 4. Mean consumption of o r i g i n a l h igh- and low-ca lor ie f lavor associated Sustacal l i q u i d by hamsters given a d d i t i o n a l t r i a l s with the f lavors reversed 30 5. Mean consumption of h igh- and low-calor ie mash by g e r b i l s in the test phase 35 6. Mean consumption of i s o c a l o r i c mash associated with a f lavor previously paired to high- or low-calor ie Sustacal by gerb i l s given add i t i ona l i s o c a l o r i c mash presentation ( ex t inc t ion t r a i n i n g ) 38 7. Mean consumption of h igh- and low-calor ie mash whose f lavors are reversed by g e r b i l s given 3 add i t i ona l days of mash presentation . . . . 4 0 8. Mean consumption of h igh- and low-calor ie mash by gerb i l s given 3 add i t i ona l days with no f lavors added to the mash 43 9. The percentage of v i s i t s to and drinks from arm locat ions that contain h i g h - c a l o r i e Sustacal l i q u i d for both hamsters and g e r b i l s 50 10. The arm preference t o t a l s , preference value, summed across t r i a l s for each hamster v i s i t i n g h igh- and low-c a l o r i e arm locat ions on the 8-arm r a d i a l maze. The arms containing h igh-ca lor i e Sustacal l i q u i d are noted for each subject 53 11. The arm preference t o t a l s , preference value, summed across t r i a l s for each g e r b i l v i s i t i n g h igh- and low-c a l o r i e arm locat ions on the 8-arm r a d i a l maze. The arms containing h igh-ca lor i e Sustacal l i q u i d are noted for each subject 56 12. The percentage of v i s i t s to baited arms for ra t s , v i i i g e r b i l s , hamsters, and mice. Data for rats from Olton , C o l l i s o n , and Werz, 1977 ; for g e r b i l s from Wilk ie and S l o b i n , 1983 ; for mice from Mizumori, Rosenzweig, and Kermisch; 1982 62 13. The percentage of v i s i t s to bai ted arms for r a t s , g e r b i l s , and hamsters averaged across subjects for each t r i a l . Data for rats from Ol ton , C o l l i s o n , and Werz, 1977 ; for g e r b i l s from Wilk ie and S l o b i n , 1983 65 14. The arm preference t o t a l s , preference value, summed across t r i a l s for each hamster v i s i t i n g arm locat ions on the 17-arm r a d i a l maze 67 15. The arm preference t o t a l s , preference value, summed across t r i a l s for each rat v i s i t i n g arm locat ions on the 17-arm r a d i a l maze. Data taken from Olton , C o l l i s o n , and Werz, 1977 69 16. The frequency of v i s i t s as a function of the arm locat ions r e l a t i v e pos i t ion to the previous v i s i t . Data for rats from Olton , C o l l i s o n , and Werz, 1977 ; for g e r b i l s from Wilkie and S l o b i n , 1 983 71 17. The percentage of correct v i s i t s to baited arms for each choice averaged across subjects in the unblocked and blocked condit ions 74 ix Acknowledgement I thank Don W i l k i e f o r h i s support and e d i t o r i a l comments. I thank Rod Wong and Jamie Smith f o r s e r v i n g as h e l p f u l members on the committee. I thank the f a c u l t y and graduate students i n the biopsychology area of the U n i v e r s i t y of B r i t i s h Columbia f o r s h a r i n g t h e i r i n t e r e s t s and equipment. :BIOSHEET 1 I . INTRODUCTION At some po int , genera l i s t foragers whose d i e t , unl ike that of a s p e c i a l i s t , cons is ts of several food items must decide which foods to eat . Omnivorous centra l place foragers such as hamsters and s q u i r r e l s may decide which foods to eat before or during a foraging bout, or after return to i t s home. According to Optimal Foraging Theory (OFT) (cf . Emlen, 1966; Hughes & Townsend, 1981; Krebs, Houston, & Charnov, 1981; Krebs, Stephens, & Sutherland, 1983; Pyke, Pul l iam, & Charnov, 1977), foragers select food in a manner that maximizes benefits and minimizes costs . The most commonly used currency representing costs and benefits i s energy measured in terms of c a l o r i c units (Schoener, 1971). Thus, animals are viewed as foraging optimal ly i f the ir c a l o r i c input outweighs the ir c a l o r i c output ( e . g . , t r a v e l expenses, handling of food, e t c . ) . Foragers, e s p e c i a l l y g e n e r a l i s t s , often remain f l e x i b l e al lowing d i f f erent foods to be selected while maintaining the same energy balance or c a l o r i c intake. The assumption that foragers e s s e n t i a l l y regulate or balance energy by means of c a l o r i c ingestion is a s i m p l i f i c a t i o n . It may be more r e a l i s t i c to define an optimal food choice by a forager as a dec is ion that grants the greatest n u t r i t i o n a l benefit while i n f l i c t i n g the least cost . N u t r i t i o n a l requirements involve more than c a l o r i c intake. Foragers must also regulate the amount of mineral and vitamin intake as well as avoid toxic substances. The ra t s ' a b i l i t y to recover from a v i tamin-def i c i ent or minera l -def ic ient diet by 2 se lec t ing foods which provide recovery is well known (Adam, 1973; Handal, 1965; H a r r i s , C lay , Hargreaves, & Ward, 1933; Rozin, 1967; Zahorik, Maier , & Pies , 1974). The ra t s ' a b i l i t y to avoid toxic compounds has a lso been widely demonstrated (Galef & C l a r k , 1971; Barnett , Cowan, Radford, & Prakash, 1975; G a r c i a , Rusiniak, & Bre t t , 1978, Melcer & Timberlake, 1985). Although the regulat ion of energy balance seems to predominate over other e s sent ia l s , in that , rats as an example w i l l not overeat c a l o r i e s in order to obtain adequate amounts of prote in (Andik, Donhoffer, Farkas, & Schmidt, 1963) or water (Bruce & Kennedy, 1951), not a l l foragers appear as optimal c a l o r i e gatherers (Giraldeau & Kramer, 1982; Lobel & Ogden, 1981; M i l t o n , 1979; Pul l iam, 1980; Rapport, 1980; Tinbergen, 1981; Vadas, 1977). The energy maximizing model of optimal foraging assumes that animals aim to maximize net intake ( i . e . , c a l o r i e s ) with no n u t r i t i o n a l cons tra in t s , with perfect knowledge of food qua l i ty and of tradeoffs with other kinds of costs or benefits (Krebs, Stephens, & Sutherland, 1983). However, in most instances, to assume that maximizing gain in terms of energy is an appropriate optimizat ion c r i t e r i o n is an e r r o r . Giraldeau and Kramer (1982), for example, found that load s ize of chipmunks carry ing seeds back to a centra l cache was cons i s tent ly smaller than predicted by an energy maximizing model. The incongruity of empir ica l f indings and the energy maximizing model may be a resul t of a foragers' need to e s tab l i sh a tradeoff among c a l o r i c balance, toxin avoidance, and 3 n o n - c a l o r i c n u t r i t i o n a l requirements when d e c i d i n g which foods to eat. The p e n a l i t y f o r f a i l i n g to maintain a proper d i e t as w e l l as a v o i d t o x i c substances can be d e l e t e r i o u s or even f a t a l . For i n s t a n c e , i n g e s t i n g a t o x i c substance can r e s u l t i n s i c k n e s s or death. A s i c k animal i s at heightened r i s k i f unable to escape p r e d a t o r s when f o r a g i n g , and at a disadvantage i f unable to t r a n s p o r t food to i t s home. Although the body has e l a b o r a t e i n t e r n a l mechanisms such as poison d e t o x i f i c a t i o n , n u t r i e n t b i o s y n t h e s i s , and n u t r i e n t storage to a v o i d the danger of e a t i n g something harmful or e a t i n g too much of a 'good' food, animals' behavior a l s o p l a y s an important r o l e i n r e g u l a t i n g n u t r i t i o n a l balance. Recent s t u d i e s suggest three b e h a v i o r a l mechanisms that an animal may use i n d i e t s e l e c t i o n . These are innate p r e f e r e n c e , s o c i a l t r a n s m i s s i o n , and experience-based a c q u i s t i o n of d i e t a r y i n f o r m a t i o n . An innate p r e f e r e n c e i n food s e l e c t i o n i s i l l u s t r a t e d by animals' p r e f e r e n c e f o r s w e e t - t a s t i n g food items (Rozin, 1976). Sweet-tasting food items represent foods with a high sugar co n t e n t . In l i g h t of OFT, choosing foods with a high sugar content and t h e r e f o r e high c a l o r i c content maximizes e n e r g e t i c i n t a k e . A c c o r d i n g l y , a g r e a t e r b e n e f i t i s d e r i v e d from i n c r e a s i n g c a l o r i c input by i n g e s t i o n of sweet foods than from i n g e s t i n g a more abundant food with l e s s sugar per food item. However, a l l behavior cannot be e x p l a i n e d by such innate mechanisms. Evidence e x i s t s f o r other c o s t - r e d u c i n g mechanisms of d i e t s e l e c t i o n . 4 Soc ia l transmission i s a cost-reducing mechanism of diet se lec t ion that allows an animal to benefit from watching the feeding behaviors of others . Galef (1984) has shown that under a wide var ie ty of experimental condi t ions , an 'observer' rat w i l l adopt the diet of a 'demonstrator' r a t . This includes rats that are wi ld and domesticated, food deprived and non-food deprived, with f a m i l i a r and unfamil iar partners , l i q u i d -dr ink ing and mash-eating, as well as young and o l d . However, most examples of s o c i a l transmission consider juveni les ' gathering of information about food q u a l i t y from watching parents food choice (Galef & Sherry, 1973; Hogan, 1977). For example, Galef and Clarke (1972) describe the transmission of d ie t preference patterns from mother rat to pup. This transmission occurs v i a two possible routes . F i r s t , rat pups may feed in the environment along with the ir mother, become f a m i l i a r with cer ta in foods, and prefer these fami l iar foods af ter weaning (Galef & Clarke , 1971, 1972). Second, information about diet q u a l i t y may be passed along to the pup v ia the mother's milk (Galef & Henderson, 1972; Galef & Sherry, 1973; LeMagnen & T a l l o n , 1966). By noting which foods are ingested, juveni les can avoid toxic foods and minimize the amount of sampling necessary in developing an adequate d i e t . We must remember that i l l n e s s as a resul t of poisoning increases the amount of energy the body needs for recovery while i n h i b i t i n g the s ick animal from gathering more food. Thus, s o c i a l transmission reduces the costs of deciding which foods to eat . Experience-based a c q u i s i t i o n of d ie tary information occurs 5 when an animal associates a sensory a t t r i b u t e of the food with d ie tary q u a l i t y . The Blue jay ' s strong avoidance response to the toxic monarch but ter f ly and i t s non-toxic mimic, the viceroy b u t t e r f l y , af ter ingestion of the toxic monarch but ter f ly (Brower, 1958) i s a good example that involves a v i s u a l s t imulus. Booth (1972) has demonstrated the ra t s ' adjustment in meal s ize using o l fac tory stimulus cues as a determinant of c a l o r i c dens i ty . Rats ate less of a d a i l y meal i f the odor associated with the meal had previously been paired with a high-carbohydrate d i e t . Th i s , too, i s an example of an experience-based diet modi f icat ion . As opposed to innate preference and s o c i a l transmission, food se lec t ion by th i s means involves a feedback system based upon t r i a l and e r r o r . That i s , an animal samples a new food, i f the food item is b e n e f i c i a l he continues to ingest the food item, i f not he avoids ingest ion . An important quest ion, however, is what i s the basis for judgement when comparing good and better foods. Avoiding a food that produces i l l n e s s is a c learcut d i s t i n c t i o n between a good and bad food. But, what d i s t i n c t i o n can be used to choose between adequate and better foods? When animals choose food, we labe l the selected food as the preferred food. If a l l members of the same species choose the same food upon i n i t i a l presentat ion, then we conclude that the animal has an innate preference for that food. If the l i k e l i h o o d of choosing a food changes due to the animals' experience with that food, we conclude that the animal has a learned preference for that food. Preferences are learned when 6 ingestion of a substance i s followed by an improvement in ' p h y s i o l o g i c a l s tate ' (Garcia , Hankins, Rusiniak, 1974; Revusky, 1967; Zahorik and Maier, 1969). Evidence for poison avoidance (good vs bad) suggests that animals learn to avoid toxic substances qu ick ly and maintain th i s avoidance behavior for long periods of time (Riley & Clarke , 1977). However, the sparse evidence for learning about the p o s i t i v e aspects of foods and the f lavors associated with them suggests that animals require long-term experience with the food, and that the behavior which i s learned is quick ly extinquished (Mehiel & B o l l e s , 1984). Thus, a di f ference in preference for adequate vs better foods i s harder to detect than a di f ference in preference for good vs bad foods. Three studies have demonstrated r a t ' s preference for f a m i l i a r - b e n e f i c i a l foods (better) over fami l iar - sa fe foods (adequate). In 1967, Revusky measured the e f fects of deprivat ion using a preference technique. Rats were condit ioned to prefer e i ther grape ju ice or milk depending upon which l i q u i d they had access to when deprived. For instance, rats in a f i r s t group were fed grape ju ice while hungry and milk while sa t ia ted , and rats in a second group recieved the opposite treatment. In a subsequent test choice , the f i r s t group preferred grape juice more than the second group. Revusky concluded that the rats ' preference for a food was greater i f the food had previously been consumed at a high deprivat ion l eve l than at a low deprivat ion l e v e l regardless of the test deprivaton. Thus, rats preferred the f a m i l i a r - b e n e f i c i a l food. In 1974, Zahorik, 7 Maier, and P i e s compared the t h i a m i n e - d e f i c i e n t r a t s ' p r e f e r e n c e between a recovery f l a v o r ( b e t t e r ) and a f a m i l i a r - s a f e food (adequate). Four groups had a d i s t i n c t i v e f l a v o r p a i r e d with a c e r t a i n phase of the experiment. That i s , f l a v o r s were presented e i t h e r before the r a t s became thiamine d e f i c i e n t ( o l d -f a m i l i a r f l a v o r ) ; while the r a t r e c i e v e d thiamine i n j e c t i o n s d u r i n g the recovery p e r i o d (recovery f l a v o r ) ; a f t e r the l a s t recovery i n j e c t i o n (new-familiar f l a v o r ) ; or f o r the f i r s t time d u r i n g the t e s t phase (novel f l a v o r ) . When given a c h o i c e between the recovery f l a v o r and the f a m i l i a r - s a f e f l a v o r or novel f l a v o r r a t s who were no longer t h i a m i n e - d e f i c i e n t p r e f e r r e d the recovery f l a v o r . Thus, they a l s o p r e f e r r e d the f a m i l i a r - b e n e f i c i a l food. More r e c e n t l y , B o l l e s , Hayward, and C r a n d a l l (1981) r e p o r t e d the r a t s ' p r e f e r e n c e f o r t a s t e s a s s o c i a t e d with higher c a l o r i e food items. B o l l e s et a l . (1981) gave two groups of r a t s s e v e r a l t r i a l s i n order to form an a s s o c i a t i o n between the f l a v o r of a food mash and i t s c a l o r i c d e n s i t y . Rats were given two foods i n t h e i r homecages. A h i g h - c a l o r i e food mash had one f l a v o r . A l o w - c a l o r i e food mash had a second f l a v o r . The c a l o r i c d e n s i t y - f l a v o r a s s o c i a t i o n was counterbalanced. Once the r a t s consumed more h i g h - c a l o r i e food mash, they were allowed to choose between the two f l a v o r s when the food mashes were of equal c a l o r i c content. The r a t s more o f t e n chose the f l a v o r p r e v i o u s l y a s s o c i a t e d with the high c a l o r i e mash. Th e i r c h o i c e of mash was r e l i a b l e and c o n s i s t e n t with t h e i r knowledge of f l a v o r as a mediating cue to c a l o r i c d e n s i t y . In a d d i t i o n to 8 demonstrating a robust e f f e c t , B o l l e s et a l . developed a procedure amenable to t e s t i n g other rodent p o p u l a t i o n s . The r o l e of c o n d i t i o n i n g i n d i e t s e l e c t i o n i s explored f u r t h e r i n t h i s t h e s i s . In p a r t i c u l a r , the rodents' use of c a l o r i c d e n s i t y i n f o r m a t i o n i s i n v e s t i g a t e d . Golden hamsters (Mesocricetus auratus) and Mongolian g e r b i l s (Meriones  u n g u i c u l a t u s ) were given a c h o i c e between a good food of adequate c a l o r i c value and a b e t t e r food of higher c a l o r i c v a l u e . B o l l e s et a l . (1981) demonstrated the e f f e c t that p r i o r c o n d i t i o n i n g of f l a v o r cues to c a l o r i c d e n s i t y has on a r a t ' s a b i l i t y to choose a h i g h - c a l o r i e food item. Thus, the f i r s t p o r t i o n of t h i s t h e s i s i s simply an extension of B o l l e s et a l . ' s work to examine the c o n d i t i o n i n g e f f e c t i n other rodent s p e c i e s . There i s a l s o a second focus i n t h i s t h e s i s . I f rodents can choose n u t r i e n t r i c h sources by i t s a s s o c i a t e d f l a v o r and w i l l use t h i s i n f o r m a t i o n as a b a s i s f o r f u t u r e d e c i s i o n s when encountering the same f l a v o r , then w i l l rodents use t h i s i n f o r m a t i o n i n a c t u a l f o r a g i n g s i t u a t i o n s ? That i s , we asked i f the a d d i t i o n of cost of t r a v e l to our o r i g i n a l two c h o i c e procedure would change the rodent's d e c i s i o n to consume high c a l o r i e foods. T r a d i t i o n a l l y , the e f f e c t of t r a v e l on rodents' f o r a g i n g has been analyzed i n a r a d i a l - a r m maze s i t u a t i o n . A r a d i a l - a r m maze c o n s i s t s of a c e n t r a l hub with a number of arms or a l l e y s r a d i a t i n g away from the c e n t r a l a r e a . T y p i c a l l y , food or water i s p l a c e d at the end of each arm. Then, animals who are food or water d e p r i v e d must l o c a t e or c o l l e c t the reward. For example, 9 Batson, Best, P h i l l i p s , P a t e l , and G i l l e l a n d (1986) examined ra t s ' preference for cer ta in arms when water and/or food deprived. They report that rats are able to a l t e r the ir preference for a r a d i a l maze arm which is empty, i s associated with a toxic substance, or contains a high q u a l i t y food source. An arm was preferred when chosen at the beginning in a sequence of eight choices . T h i r s t y rats who foraged for water rewards on an 8-arm r a d i a l maze decreased the i r preference for an empty arm. Rats that learned a sacchar in - l i th ium assoc iat ion e i ther on the maze or in the ir homecage decreased the ir preference for an arm containing saccharin . When food and water deprived, rats increased the i r preference for an arm containing a sweet chocolate milk s o l u t i o n . Thus, Bateson et a l . i l l u s t r a t e d the rats ' a b i l i t y to a l t e r the ir preference for a food s i t e (arm locat ion) when n u t r i t i o n a l needs changed or the qua l i ty of the food item changed. In the second set of studies reported in th i s thes i s , both g e r b i l s and hamsters were placed within a foraging s i tua t ion on an 8-arm r a d i a l maze where one-half of the arms were baited with a h i g h - c a l o r i e l i q u i d and one-half with a low-calor ie l i q u i d . Although, I expect the rodents to f i r s t v i s i t those arms baited with the h i g h - c a l o r i e l i q u i d , th i s may not be the case. A secondary purpose of th i s thes is was to examine the foraging strategy of hamsters in the radia l -arm maze. The foraging s trategies that are observed in a radia l -arm maze s i tua t ion vary among species . Since Ol ton , C o l l i s o n , and Werz's (1977) inves t igat ion of the r a d i a l maze performance of r a t s , at 10 l e a s t s i x other s p e c i e s have been t e s t e d i n the r a d i a l - a r m maze. These are Mongolian g e r b i l s (Meriones u n g u i c u l a t u s ) ( W i l k i e & S l o b i n , 1 9 8 3 ) , CD-1 mice (Mus) (Mizumori, Rosenzweig, Se Kermisch, 1 9 8 2 ) , r i n g doves ( S t r e p t o p e l i a r i s o r i a ) ( W i l k i e , Spetch, & Chew, 1 9 8 1 ) , domestic pigeons (Columba l i v i a ) (Bond, Cook, & Lamb, 1981 ; Roberts & Van Veldhuizen, 1 9 8 5 ; Spetch & Edwards, 1 9 8 6 ) , Savannah sparrows (Passerculus sandwichensis) (Moore & Osadchuk, 1 9 8 2 ) , and Siamese f i g h t i n g f i s h (Betta  splendens) ( R o i t b l a t , Tham, & Golub, 1 9 8 2 ) . A f o r a g i n g s t r a t e g y can be c h a r a c t e r i z e d as e i t h e r a response s t r a t e g y based on a l g o r i t h m i c responding or a memory-based s t r a t e g y r e l y i n g on environmental cues. One response s t r a t e g y i s to v i s i t s u c c e s s i v e arms in a c h o i c e sequence in a c l o c k w i s e (+) or a n t i - c l o c k w i s e (-) d i r e c t i o n (Foreman, 1 9 8 5 ) . For i n s t a n c e , a subject may v i s i t each arm ( + 1 ) , or s k i p two arms and v i s i t the arm which i s three arms away from the l a s t c h o i c e (+3 ) . We look f o r response p a t t e r n s by showing the frequency of s e l e c t i o n ( e.g., 20 v i s i t s ) dependent upon the number of arms d i s t a n c e from the arm j u s t v i s i t e d (e.g. + 1 ) . A d i s t r i b u t i o n that i s peaked and unimodal i l l u s t r a t e s a l g o r i t h m i c responding. I f the peak i s + or - 1 , then the subject v i s i t s each arm c o n s e c u t i v e l y . The c o n s e c u t i v e arm p a t t e r n (+ or -1) i s u s u a l l y seen on l a r g e mazes (Olton & Werz, 1 9 7 8 ) . An a l g o r i t h m i s not c o n s i d e r e d as evidence f o r s p a t i a l memory because choice i s independent of food l o c a t i o n (Eckerman, 1 9 8 0 ) . Siamese f i g h t i n g f i s h use of a response s t r a t e g y when f o r a g i n g on the r a d i a l - a r m maze i s a good example (Bond, Cook, & Lamb, 11 1981). Rats and g e r b i l s , on the other hand, perform more e f f e c i e n t l y on the radia l -arm maze and may use a memory-based strategy (cf . Ol ton , 1978; Roberts, 1984). The ra t s ' a b i l i t y to avoid entering unbaited arms seems to be c o n t r o l l e d by extramaze v i s u a l cues that d i s t i n q u i s h various locat ions (Olton & C o l l i s o n , 1979; Zoldeck & Roberts, 1978). A l so , the order of se lect ions var ies from t r i a l to t r i a l and subject to subject , implying that accurate performance is not simply a resu l t of learning a p a r t i c u l a r route through the maze (Olton & Samuelson, 1976). However, rats foraging on the radia l -arm maze have also been known to use a response strategy (Foreman, 1985; Yoerg & Kamil , 1982). Response patterning appears to complement rather than replace the rats ' use of a s p a t i a l representation of the environment. The rats ' use of e i ther a response or memory-based strategy was large ly determined by the task procedure employed by the experimenter. Ring doves (Wilkie & S l o b i n , 1983) and pigeons (Roberts & Van Veldhuizen, 1985) w i l l a lso d i sp lay accurate working s p a t i a l memory when given spec ia l and extended t r a i n i n g on the t r a d i t i o n a l radia l -arm maze. Savannah sparrows also perform accurately when tested outdoors in an 8-arm r a d i a l maze (Moore & Osadchuck). For pigeons, demonstration of a working s p a t i a l memory i s a recent d iscovery . Bond, Cook, and Lamb (1981) compared the performance of rats and pigeons on the same 8-arm r a d i a l maze and found lower accuracy in the pigeons. They suggested that the pigeons' performance was a resul t of having 12 been f o r c e d to feed i n an u n n a t u r a l s e t t i n g . A c c o r d i n g l y , Spetch and Edwards (1986) allowed pigeons to feed i n o p e n - f i e l d environments with e i g h t e l e v a t e d food s i t e s . In t h i s more n a t u r a l i s t i c s e t t i n g , pigeons d i s p l a y e d evidence of working s p a t i a l memory w i t h i n a few t r i a l s . The pigeons' use of a f o r a g i n g s t r a t e g y , l i k e t h a t of the r a t , seems to depend upon the task procedure employed by the experimenter. Mice, u n l i k e r a t s and pigeons, f o r a g i n g on a r a d i a l - a r m maze gave no evidence of improved performance beyond that e x h i b i t e d d u r i n g the f i r s t few days of t r a i n i n g (Mizumori, Rosenzweig, & Kermisch, 1982). Although mice d i d choose b a i t e d arms at accuracy l e v e l s above chance, Mizumori et a l . concluded that t h e i r performance c a l l e d f o r t h the need to q u e s t i o n the use of r a d i a l - a r m mazes as an i n d i c a t o r of innate food-search b e h a v i o r s . In p a r t i c u l a r , Mizumori et a l . s t a t e d that other s p e c i e s ' performance on the r a d i a l - a r m maze should be exp l o r e d i n order to i n v e s t i g a t e the c o m p a r a b i l i t y of food-search behaviors i n the f i e l d , v a r i a b l e s that a f f e c t search behaviors, and how these f a c t o r s d i r e c t l y i n f l u e n c e r a d i a l - a r m maze performance. The f o r a g i n g s t r a t e g y of another commonly s t u d i e d rodent -the hamster - on a r a d i a l - a r m maze i s unexplored. Thus, in a f i n a l study, hamsters were allowed to forage on a r a d i a l maze where arms were b a i t e d e q u a l l y with a s i n g l e sunflower seed. T h i s study served two purposes. F i r s t , the hamsters' performance can be compared to other s p e c i e s . Second, the hamsters' performance can be compared to hamsters' performance 13 i n a maze which i s unequally b a i t e d ( v i z . Experiment 2) . 1 4 I I . EXPERIMENT 1 The purpose of Experiment 1 was to r e p l i c a t e B o l l e s et a l . (1981) i n order t o t e s t the robustness and u n i f o r m i t y of the f l a v o r - c a l o r i e c o n d i t i o n i n g phenomenon a c r o s s s p e c i e s . Golden hamsters and Mongolian g e r b i l s were given experience with two d i e t s , one high i n c a l o r i e s and one low i n c a l o r i e s . Each d i e t was marked by a d i s t i n c t i v e f l a v o r . D i e t s were e i t h e r l i q u i d or a mash. The c o n d i t i o n i n g of f l a v o r p r e f e r e n c e s was assessed by the degree t o which s u b j e c t s p r e f e r r e d the h i g h - c a l o r i e f l a v o r i n a choice t e s t i n which the two f l a v o r s were p l a c e d i n d i e t s of i s o c a l o r i c d e n s i t i e s . Experiment 1 c o n s i s t s of three p a r t s : mash pr e f e r e n c e of hamsters, l i q u i d p r e f e r e n c e of hamsters, and mash p r e f e r e n c e of g e r b i I s . 1. PART 1 1.1 Method 1.1.1 Subjects S i x t e e n e x p e r i m e n t a l l y naive Golden hamsters (Mesocricetus  auratus) ( e i g h t female, e i g h t male) were i n d i v i d u a l l y housed i n wire mesh cages (24 cm x 18 cm x 17 cm) on a reversed 12-hr l i g h t / 12-hr dark c y c l e (dark c y c l e began at 8:00 a.m.). They were t e s t e d d u r i n g the l a s t t h i r d of the dark c y c l e . They had u n l i m i t e d access to water. 15 1.1.2 Mater ia l s During the condi t ioning phase, a subject was given access in i t s homecage to a s ingle 2.5 cm t a l l paper cup that contained a f lavored mash. The cup was glued to a 13 cm x 8 cm x 5 cm wooden base. During the test phase, a subject was given access in i t s homecage to two cups that contained f lavored mash. The cups were glued to a 13 cm x 8 cm x 5 cm wooden base and separated by a 5 cm x 5 cm wooden p a r t i t i o n . The h i g h - c a l o r i e mash consisted of the fo l lowing: 100 g Canadian corn starch (Best Foods), 13 g generic vegetable o i l , 38.5 g Purina lab chow, 10 g f l avor , and 100 ml water. This mixture was about 5.0 c a l o r i e s per gram. The low-ca lor ie mash contained no s tarch . Ca lor ie s were reduced by subs t i tu t ing a lpha-ce l lu lose f iber for s tarch . A lpha-ce l lu lose f iber i s i n d i g e s t i b l e and therefore has no c a l o r i e s . Thus, the low-c a l o r i e mash consisted of the fo l lowing: 100 g a lpha-ce l lu lose f iber (National Biochemical C o r p . ) , 13 g generic vegetable o i l , 38.5 g Purina lab chow, 10 g f l avor , and 100 ml water. This mixture was about 1.0 c a l o r i e s per gram. Flavors were provided by adding to the d ie ts rasberry and strawberry extract (Club House). Body weights and food mash weights were measured to the nearest gram by using a standard laboratory sca le . 16 1.1.3 P r o c e d u r e On c o n d i t i o n i n g d a y s , t h e s u b j e c t s had a d l i b a c c e s s t o w a t e r a n d a s i n g l e f l a v o r e d mash. The s u b j e c t s were p r e s e n t e d w i t h 30 g o f h i g h - o r l o w - c a l o r i e mash on a l t e r n a t e d a y s . E a c h d i e t was f l a v o r e d w i t h e i t h e r r a s b e r r y o r s t r a w b e r r y . F o r e i g h t s u b j e c t s ( f o u r f e m a l e , f o u r m a l e ) r a s b e r r y f l a v o r i n g was a d d e d t o t h e h i g h - c a l o r i e d i e t a n d s t r a w b e r r y t o t h e l o w - c a l o r i e d i e t . The f l a v o r s were r e v e r s e d f o r t h e o t h e r e i g h t s u b j e c t s . C o n s u m p t i o n was m e a s u r e d a t t h e end o f e a c h 2 4 - h r p e r i o d . ( P i l o t s t u d i e s s u g g e s t e d t h a t s p i l l a g e was n e g l i g i b l e ; c o n s e q u e n t l y , t h i s m ethod o f m e a s u r i n g c o n s u m p t i o n was p o s s i b l e . ) On t h e t h i r d d a y , t h e t e s t f o o d was r e p l a c e d by s t a n d a r d l a b o r a t o r y chow i n o r d e r t o e n s u r e t h a t p r o p e r n u t r i e n t r e q u i r e m e n t s were m a i n t a i n e d . The f o u r t h day was a d e p r i v a t i o n day when n e i t h e r t e s t f o o d n o r l a b o r a t o r y chow was a v a i l a b l e . T h i s c y c l e was r e p e a t e d f o u r t i m e s p r i o r t o t h e t e s t p h a s e . A l t h o u g h B o l l e s e t a l . o n l y r e p e a t e d t h e c y c l e t w i c e p r i o r t o t h e t e s t p h a s e , p r e l i m i n a r y s t u d i e s s u g g e s t e d t h a t h a m s t e r s were n o t a s r e a d i l y c o n d i t i o n e d t o t a s t e c u e s a s r a t s . On t e s t d a y s , t h e s u b j e c t s were o f f e r e d two c u p s o f f o o d , b u t a t t h i s t i m e t h e f o o d i n b o t h c u p s was t h e same, c o n s i s t i n g o f a m i x t u r e o f e q u a l p r o p o r t i o n s o f t h e h i g h - a n d l o w - c a l o r i e d i e t s . The o n l y d i f f e r e n c e b e t w e e n t h e two t e s t d i e t s was t h e a d d i t i o n of t h e f l a v o r s t h a t h a d p r e v i o u s l y b een c o r r e l a t e d w i t h c a l o r i c d e n s i t y . D u r i n g t h e f i r s t 5 min o f t e s t i n g , s u b j e c t s were t e s t e d i n g r o u p s of two so t h a t t h e e x p e r i m e n t e r c o u l d r e c o r d t h e amount o f t i m e s p e n t e a t i n g , s n i f f i n g o r t r a n s p o r t i n g 1 7 the c ontents of each cup. E a t i n g i s d e f i n e d as the a c t u a l consumption of mash or the act of p u t t i n g mash i n t o the cheekpouch. S n i f f i n g i s noted when the sub j e c t stands on h i s hind l e g s over the mash. Being next to the food cups on a l l four paws i s not c o n s i d e r e d as s n i f f i n g . A measure of t r a n s p o r t i n g was i n c l u d e d because s u b j e c t s t r a n s p o r t e d e i t h e r the food cups or cheekpouch contents to the corner of the cage where they s t o r e d t h e i r food. The amount of time spent engaged in at l e a s t one of these a c t i v i t i e s was tracked on a stopwatch. A c c o r d i n g l y , the t o t a l measure was a composite of the amount of time spent e a t i n g , s n i f f i n g , or t r a n s p o r t i n g mash. Consumption of mash was measured a f t e r the f i r s t hour and again a f t e r 24 hr. The d i e t that was v i s i t e d f i r s t was a l s o recorded. A f t e r the f i r s t t e s t day, a l l s u b j e c t s spent the next 24 hr with ad l i b access to l a b o r a t o r y chow. T h i s was followed by a 24-hr d e p r i v a t i o n p e r i o d . A f t e r t h i s d e p r i v a t i o n day, a second t e s t day i d e n t i c a l to the f i r s t occured. 1.1.4 S t a t i s t i c s When a n a l y z i n g measures of mash and l i q u i d consumption or time spent e a t i n g , s n i f f i n g , and t r a n s p o r t i n g mash du r i n g the f i r s t 5 min of o b s e r v a t i o n , a within-group a n a l y s i s of v a r i a n c e with two f i x e d f a c t o r s , t r i a l and c a l o r i c d e n s i t y (high or low), was used. An i n t e r a c t i o n between the amount of mash or l i q u i d consumed per t r i a l and c a l o r i c d e n s i t y demonstrates the c o n d i t i o n i n g e f f e c t . That i s , c o n d i t i o n i n g occurs when an in c r e a s e i n h i g h - c a l o r i e consumption i s coupled with a decrease in l o w - c a l o r i e consumption. E x t i n c t i o n produces the opposite 18 e f f ec t . In order to conclude that condit ioning or ex t inc t ion has occurred the measure of h i g h - c a l o r i e consumption must be greater than low-calor ie consumption af ter the condi t ioning phase (condit ioning) or equal to low-calor ie consumption af ter the test phase ( ex t inc t ion ) . Although the amount of time spent eat ing , s n i f f i n g or transport ing the high- and low- c a l o r i e mash during the f i r s t 5 min of observation may not agree with the measures of mash consumption, in nearly every case they did agree. Therefore, for a l l parts of Experiment 1, only the consumption measures are reported. 1.1.5 Results And Discussion Figure 1 shows consumption of i s o c a l o r i c d iets during test t r i a l s . During th i s phase, hamsters d id not consume more of the mash whose f lavor was previously associated to the h i g h - c a l o r i e mash ( M =5.58 g, 16.79 g) than the mash whose f lavor was previously associated to the low-ca lor ie mash ( M =5.73 g, 18.58 g) af ter 1 hr [ F (1,15)= 0.0656, 2 =.7889] nor after 24 hr [ F (1 , 15) = 1 .7683, p_ = .2013]. After 1 hr , hamsters ate an equal amount of i s o c a l o r i c f lavored mash. After 24 hr , hamsters a c t u a l l y ate a greater amount of mash whose f lavor was previous ly associated to the low-ca lor ie mash. Thus, hamsters did not demonstrate the f l a v o r - c a l o r i e condi t ioning e f f e c t . When consumption was measured after 1 hr , hamsters had consumed more mash during the f i r s t test t r i a l ( M =6.83 g) than the second test t r i a l ( M =4.48 g) [ F (1 ,1 5) = 1 9. 0452, p_ = .0008], When consumption was measured after 24 hr , hamsters 19 F i g u r e 1 - Mean c o n s u m p t i o n o f i s o c a l o r i c mash whose f l a v o r s were p r e v i o u s l y p a i r e d w i t h a h i g h - o r l o w - c a l o r i e mash by h a m s t e r s a f t e r 1 h r a n d 24 h r . 1 HOUR 21 consumed more mash during the second test t r i a l ( M =20.10 g) than the f i r s t test t r i a l ( M =15.18 g) . [ F (1 , 1 5) =48.8433 , p_ =.0000], Hamsters' consumption of mash across t r i a l s appears to switch from immediate feeding to delayed feeding. Recal l that u n t i l the test phase, hamsters had been presented with one mash per condi t ioning t r i a l or 30 g of mash per day. Perhaps, the a v a i l a b i l i t y of twice as much mash (60 g) a l t ered the ir feeding strategy. When presented with a small amount of food, hamsters may eat larger but fewer meals per day. When presented with a large amount of food, hamsters may prefer to eat smaller but more meals per day. The amount of i s o c a l o r i c mash hamsters consumed was independent of the t r i a l number when measured af ter I hr [ F (1,15)=0.0314, p =0.8380] and 24 hr [ F (1,15)=2.7200, g =.1168] (Figure 1). The hamsters appear to eat an equal amount of i s o c a l o r i c mash af ter 1 hr and 24 hr in both t r i a l s . Hamsters showed no preference towards v i s i t i n g e i ther f lavored i s o c a l o r i c mash f i r s t . Choice of each f lavored mash was equally l i k e l y . Those hamsters with a h i g h - c a l o r i e rasberry f lavor assoc iat ion chose rasberry mash 9 times in 16 t r i a l s (56%). Those hamsters with a h i g h - c a l o r i e strawberry - f lavor assoc iat ion chose strawberry mash 7 times in 16 t r i a l s (44%). 2. PART 2 In Part 1, the hamsters d id not show a s i g n i f i c a n t f l a v o r -c a l o r i e condi t ioning e f f ec t . This outcome d i f f e r s from that reported by Bol les et a l . (1981) for r a t s . One reason for th i s discrepancy may be that Bol les et a l . ' s o r i g i n a l procedure was 22 not f o l l o w e d e x a c t l y . Because i n p i l o t s t u d i e s we found that hamsters s t o r e d food mash i n t h e i r cheekpouches, a s i n g l e mash had to be presented on a l t e r n a t e days i n order to prevent cheekpouching. Since the o r i g i n a l mashes were d i f f e r e n t c o l o r s , when cheekpouched a b a l l of mash c o n s i s t i n g of more than one c o l o r c o u l d be d i s c o v e r d i n the hamsters' food cache. If hamsters cheekpouch and sample both d i e t mixes, then the mash no longer can be i d e n t i f i e d by one f l a v o r - c a l o r i e a s s o c i a t i o n . Simultaneous sampling of mash d u r i n g the c o n d i t i o n i n g phase r e s u l t s i n a mixture that resembles the i s o c a l o r i e mixture presented i n the t e s t phase. However, B o l l e s et a l . ' s procedure i n v o l v e d simultaneous p r e s e n t a t i o n of the low- and h i g h - c a l o r i e mash. Consequently in Part 2, v a n i l l a and c h o c o l a t e S u s t a c a l (a milky l i q u i d substance) was s u b s t i t u t e d f o r the f l a v o r e d mash because cheekpouching of a l i q u i d substance i s u n l i k e l y . With t h i s m o d i f i c a t i o n , we were able to present low- and h i g h - c a l o r i e d i e t s s i m u l t a n e o u s l y . 2.1 Method 2.1.1 Subjects The same su b j e c t s that served i n Part 1 were used. 2.1.2 M a t e r i a l s During the c o n d i t i o n i n g and t e s t phase, a sub j e c t was given access i n i t s homecage to two 50 ml tubes of S u s t a c a l (a milky l i q u i d substance manufactured by Mead Johnson which i s used as a d i e t a r y supplement). The h i g h - c a l o r i e S u s t a c a l l i q u i d c o n s i s t e d of 145 ml of 23 Sustacal to 290 ml of water. This mixture was 3.4 c a l o r i e s per ml . The low-ca lor ie Sustacal l i q u i d consisted of 90 ml of Sustacal to 300 ml of water. This mixture was 2.3 c a l o r i e s per ml. Sustacal i s manufactured in both v a n i l l a and chocolate f l a v o r s . Therefore, no add i t iona l extract was needed in order to f lavor each d i e t . 2.1 .3 Procedure During the condi t ioning phase, the subjects had ad l i b access to water and 1 - h r access to both Sustacal l i q u i d d i e t s . Placement of the tubes on the l e f t or r ight side of the homecage was randomized. For eight subjects (four female, four male) v a n i l l a Sustacal was the h i g h - c a l o r i e d iet and chocolate the low-calor ie d i e t . The f lavors were reversed for the other eight subjects . Consumption was measured once, at the end of a 1 - h r per iod . (Sustacal l i q u i d must be r e f r i g e r a t e d . Thus, consumption measures past 1 hr would be confounded by spoilage e f f ec t s . ) Subjects were given one p e l l e t (approximately 5g) of laboratory chow fol lowing l i q u i d presentat ion . After 2 days of condi t ion ing , a 24-hr deprivat ion period when no food or Sustacal l i q u i d was ava i lab le was implemented. This cyc le was repeated four times p r i o r to the test phase. On test days, the subjects were offered both tubes, but at th i s time the l i q u i d in both tubes were of equal c a l o r i c densi ty , cons i s t ing of an equal mixture of both d i e t s . The only di f ference between the two .tubes was the f lavors that had previously been corre la t ed with c a l o r i c densi ty . Consumption was measured at the end of a 1 -hr per iod . Subjects were given 24 one p e l l e t (approximately 5g) of l a b o r a t o r y chow f o l l o w i n g l i q u i d p r e s e n t a t i o n . F i v e c o n s e c u t i v e t e s t days were implemented before four s u b j e c t s , two from each group (one male, one female) were randomly chosen to serve i n a f u r t h e r t e s t . T h i s group of four s u b j e c t s r e c e i v e d 5 more days of t e s t i n g with the o r i g i n a l h i gh-and l o w - c a l o r i e d i e t s but with the v a n i l l a and c h o c o l a t e f l a v o r s r e v e r s e d . The f l a v o r s - r e v e r s e d group was added to t e s t the t e n a c i t y of the c o n d i t i o n e d f l a v o r p r e f e r e n c e s when the uncondit i o n e d stimulus c o n d i t i o n s were re v e r s e d . That i s , to compare the s t r e n g t h of the c o n d i t i o n e d stimulus to the uncondit i o n e d s t i m u l u s . 2.1.4 S t a t i s t i c s 1 Data from the c o n d i t i o n i n g and t e s t phases are analyzed with the same experimental design o u t l i n e d i n the s t a t i s t i c s s e c t i o n of Part 1 (Sec. 1.1.4). Data from the f l a v o r s - r e v e r s e d group were a l s o analyzed with the same experimental design, a w i t h i n group design with two f i x e d f a c t o r s , t r i a l and c a l o r i c d e n s i t y (high or low). A switch to the h i g h - c a l o r i e l i q u i d , which now has the opposite f l a v o r than i t had o r i g i n a l l y , i s evidenced by a higher consumption measure f o r the h i g h - c a l o r i e l i q u i d . 25 2.1.5 Results And Discussion As shown in Figure 2, hamsters consumed more high c a l o r i e l i q u i d during the condit ioning phase [ F (1,15)=42.6651, 2 =.0001]. In the test phase, hamsters also consumed more of the i s o c a l o r i c l i q u i d whose f lavor was previously paired with a h i g h - c a l o r i e l i q u i d [ F (1,15)=22.0693, 2 =.0005] (Figure 2). Although hamsters were w i l l i n g to sample from both i s o c a l o r i c d iet mixes, they did consume more h i g h - c a l o r i e l i q u i d . Thus, they did demonstrate the f l a v o r - c a l o r i e condit ioning e f f ec t . As shown in Figure 3, over test t r i a l s consumption of the i s o c a l o r i c l i q u i d s whose f lavors were previously paired to high-or low-ca lor ie Sustacal converged. This increase in consumption of the i s o c a l o r i c l i q u i d whose f lavor was previously paired to the low-ca lor ie l i q u i d coupled with the decrease in the consumption of the l i q u i d whose f lavor was previously paired to the h i g h - c a l o r i e l i q u i d represents ex t inc t ion [ t r i a l x f lavor i n t e r a c t i o n ; F (4,60)=5.5475, 2 =.0010], Thus, within 5 t r i a l s of i s o c a l o r i c presentation hamsters no longer preferred the f lavor which previously represented a h igh -ca lor i e food. The f l a v o r - c a l o r i e condit ioning effect appears to be eas i ly extinguished in hamsters. When hamsters were given 5 a d d i t i o n a l days with the f lavors reversed, there was a marginal d i f ference in the amount of l i q u i d consumed [ F (1,3)=8.4440, 2 =.0639]. Hamsters consumed an average of 7.45 ml of the l i q u i d whose f lavor was o r i g i n a l l y paired with h i g h - c a l o r i e Sustaca l , but i s now paired with low-c a l o r i e Sustacal and an average of 6.78 ml of the l i q u i d whose 26 F i g u r e 2 - Mean consumption of h i g h - and l o w - c a l o r i e S u s t a c a l l i q u i d by hamsters d u r i n g the c o n d i t i o n i n g and t e s t phases. CONDITIONING TEST 28 F i g u r e 3 - Mean c o n s u m p t i o n o f i s o c a l o r i c l i q u i d a s s o c i a t e d w i t h a f l a v o r p r e v i o u s l y p a i r e d t o h i g h - o r l o w -c a l o r i e S u s t a c a l by h a m s t e r s i n t h e t e s t p h a s e . TEST 30 F i g u r e 4 - Mean consumption of o r i g i n a l h i g h - and low-c a l o r i e f l a v o r a s s o c i a t e d S u s t a c a l l i q u i d by hamsters given a d d i t i o n a l t r i a l s with the f l a v o r s r e v e r s e d . FLAVORS 2 + 0-1 1 1 1 , 1 2 3 4 § TRIAL 32 f l a v o r was o r i g i n a l l y p a i r e d w i t h l o w - c a l o r i e S u s t a c a l , b u t i s now p a i r e d w i t h h i g h - c a l o r i e S u s t a c a l . A l t h o u g h o v e r a l l c o n s u m p t i o n m e a s u r e s i n d i c a t e t h a t h a m s t e r s c o n t i n u e d t o p r e f e r t h e o r i g i n a l h i g h - c a l o r i e - f l a v o r a s s o c i a t i o n , t h e m a r g i n a l l y s i g n i f i c a n t [ F (4,1 2) = 2 .8001 , p_ =.0742] i n t e r a c t i o n b e t w e e n t r i a l a n d c a l o r i c d e n s i t y d e p i c t s an i n c r e a s e i n c o n s u m p t i o n o f t h e o r i g i n a l l o w - c a l o r i e - f l a v o r l i q u i d p a i r ( i . e . , h i g h - c a l o r i e l i q u i d ) a n d a d e c r e a s e i n t h e c o n s u m p t i o n o f o r i g i n a l h i g h - c a l o r i e - f l a v o r l i q u i d p a i r ( i . e . , l o w - c a l o r i e l i q u i d ) ( F i g u r e 4 ) . I n F i g u r e 4, t h e h i g h - c a l o r i e m e a s u r e r e f e r s t o t h e i s o c a l o r i c l i q u i d whose f l a v o r was p r e v i o u s l y p a i r e d t o a h i g h - c a l o r i e d i e t b u t i s now, upon p r e s e n t a t i o n , p a i r e d t o a l o w - c a l o r i e d i e t ; a n d v i c e v e r s a f o r t h e l o w - c a l o r i e m e a s u r e . T h u s , a s w i t c h i n p r e f e r e n c e a p p e a r s t o h a v e b e g u n . T h e r e f o r e , h a m s t e r s w i l l d e c r e a s e t h e i r p r e f e r e n c e f o r a f o o d when t h e f l a v o r a s s o c i a t e d w i t h t h a t f o o d no l o n g e r r e p r e s e n t s a h i g h e r q u a l i t y f o o d . As w e l l , h a m s t e r s w i l l a d o p t a p r e f e r e n c e f o r a f o o d whose f l a v o r h a s r e c e n t l y b e en p a i r e d w i t h an e n r i c h e d f o o d . 3. PART 3 I n P a r t 1 h a m s t e r s e x p o s e d t o a s u c c e s s i v e d i s c r i m i n a t i o n p r o c e d u r e d i d n o t d e m o n s t r a t e t h e f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t . I n P a r t 2 h a m s t e r s e x p o s e d t o a s i m u l t a n e o u s d i s c r i m i n a t i o n p r o c e d u r e d i d d e m o n s t r a t e t h e f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t , b u t t h e e f f e c t was l e s s r o b u s t t h a n t h a t d i s c o v e r e d by B o l l e s e t a l . ( 1 9 8 1 ) when r a t s s e r v e d a s s u b j e c t s . As o p p o s e d t o r a t s , h a m s t e r s were more w i l l i n g t o e a t 33 or d r i n k both a v a i l a b l e mashes or l i q u i d s . Because of t h i s apparent s p e c i e s d i f f e r e n c e , a study of f l a v o r - c a l o r i e a s s o c i a t i o n i n another s p e c i e s was warranted. Thus, i n Part 3 f l a v o r e d mash was presented to Mongolian g e r b i l s i n the same f a s h i o n as Part 1. 3.1 Method 3.1.1 S u b j e c t s S i x t e e n e x p e r i m e n t a l l y naive Mongolian g e r b i l s (Meriones  u n q u i c u l a t u s ) (eight female, e i g h t male) were housed i n d i v i d u a l l y in opaque-sided cages in a colony on a reversed 12-hr l i g h t / 12-hr dark (dark c y c l e began at 8:00 a.m.). They had u n l i m i t e d access to water. 3.1.2 M a t e r i a l s The m a t e r i a l s were i d e n t i c a l to those used i n Part 1. 3.1.3 Procedure The procedure was i d e n t i c a l to that used i n Part 1 except that the g e r b i l s were only o f f e r e d 1Og of each d i e t , and a f t e r completion of the 4 t e s t days the group was randomly d i v i d e d i n t o three groups. One group r e c e i v e d three more days of t e s t i n g ( e x t i n c t i o n group), one group r e c e i v e d three more days of t e s t i n g with the o r i g i n a l h i g h - and l o w - c a l o r i e d i e t s but with the r a s b e r r y and strawberry f l a v o r s r eversed, and one group r e c e i v e d three more days of t e s t i n g with the o r i g i n a l h i gh- and l o w - c a l o r i e d i e t s with no f l a v o r s added. The e x t i n c t i o n group was added to t e s t the t e n a c i t y of the c o n d i t i o n i n g e f f e c t . 34 Since hamsters had 5 days of i s o c a l o r i c presentation and gerb i l s had only two, three more days of i s o c a l o r i c presentation allows us to roughly compare the ex t inc t ion rate (or the tenacity of the condi t ioning ef fect) between species . The f lavors-reversed group was added to test the tenaci ty of these preferences when the unconditioned stimulus condit ions were reversed. The no f lavors group was added to test i f propert ies other than taste are being used as cues for d ie t choice . 3.1.4 S t a t i s t i c s Data from the test phase and a d d i t i o n a l test condit ions are analyzed with the same experimental design out l ined in the s t a t i s t i c s sect ion of Part 2 (Sec 2 .1 .4 ) . If g e r b i l s continue to prefer the i s o c a l o r i c mash whose f lavor was previous ly paired with h i g h - c a l o r i e mash, then we can conclude that the condit ioning ef fect i s robust. If g e r b i l s choose the h i g h - c a l o r i e mash when no f lavors are added to the mash, then we can assume that other cues in addit ion to tas te , such as texture or odor cues, may a id in detect ing the h igh-c a l o r i e mash. 3.1.5 Results And Discussion As shown in Figure 5, g e r b i l s consumed more of the i s o c a l o r i c mash whose f lavor was previously associated with h i g h - c a l o r i e mash [ F (1 ,1 5) =60.9009, p_ =.0000]. Thus, gerb i l s d id demonstrate the f l a v o r - c a l o r i e condi t ioning e f f ec t . Unlike hamsters, th i s ef fect was robust. As compared to hamsters, g e r b i l s were less l i k e l y to sample from the i s o c a l o r i c mash 35 ure 5 - Mean consumption of hi g h - and l o w - c a l o r i e mash by g e r b i l s i n the t e s t phase. 37 whose f l a v o r was p r e v i o u s l y p a i r e d t o t h e l o w - c a l o r i e mash. When g e r b i l s were g i v e n e x t e n d e d p r e s e n t a t i o n o f t h e i s o c a l o r i c mash, g e r b i l s c o n t i n u e d t o p r e f e r t h e mash whose f l a v o r was p r e v i o u s l y a s s o c i a t e d w i t h h i g h - c a l o r i e mash [ F (1 ,3)=9.0561, 2 = . 0 5 9 0 ] . G e r b i l s consumed a mean 4.39 a n d 1.37 g o f i s o c a l o r i c mash whose f l a v o r was p r e v i o u s l y a s s o c i a t e d w i t h h i g h - c a l o r i e a n d l o w - c a l o r i e mash, r e s p e c t i v e l y . F i g u r e 6 i l l u s t r a t e s t h e s t r e n g t h o f t h e c o n d i t i o n i n g e f f e c t a c r o s s t r i a l s . No i n t e r a c t i o n e x i s t e d b e t w e e n c o n s u m p t i o n p e r t r i a l a n d c a l o r i c d e n s i t y [ F ( 2 , 6 ) = 1 . 2 0 9 7 , 2 =.3629]. T h u s , u n l i k e h a m s t e r s , t h e f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t i s n o t e a s i l y e x t i n g u i s h e d i n g e r b i l s . When g i v e n 3 a d d i t i o n a l d a y s w i t h t h e f l a v o r s r e v e r s e d , g e r b i l s e x c l u s i v e l y consumed t h e h i g h - c a l o r i e mash whose f l a v o r was o r i g i n a l l y p a i r e d w i t h l o w - c a l o r i e mash. [ F (1 ,3)=83.2328, 2 =.0055], G e r b i l s consumed 4.57 g a n d 0.0 g o f t h e h i g h - a n d l o w - c a l o r i e mash, r e s p e c t i v e l y . A l t h o u g h no i n t e r a c t i o n was o b s e r v e d b e t w e e n t h e amount o f mash consumed p e r t r i a l a n d c a l o r i c d e n s i t y [ F ( 2 , 6 ) = 2 . 7 0 3 7 , 2 =.1452], F i g u r e 7 i l l u s t r a t e s t h e s t r o n g a v o i d a n c e o f l o w -c a l o r i e mash ( i . e . , t h e mash whose f l a v o r was o r i g i n a l l y p a i r e d t o t h e h i g h - c a l o r i e mash) by g e r b i l s . I n F i g u r e 7, t h e h i g h -c a l o r i e m e a s u r e r e f e r s t o t h e i s o c a l o r i c mash whose f l a v o r was p r e v i o u s l y p a i r e d t o a h i g h - c a l o r i e mash b u t i s now, upon p r e s e n t a t i o n , p a i r e d t o a l o w - c a l o r i e d i e t ; a n d v i c e v e r s a f o r t h e l o w - c a l o r i e m e a s u r e . T h u s , g e r b i l s r e a d i l y s w i t c h e d t h e i r mash p r e f e r e n c e i n a c c o r d a n c e w i t h mash q u a l i t y r e g a r d l e s s o f 38 F i g u r e 6 - Mean c o n s u m p t i o n o f i s o c a l o r i c mash a s s o c i a t e d w i t h a f l a v o r p r e v i o u s l y p a i r e d t o h i g h - o r l o w - c a l o r i e S u s t a c a l by g e r b i l s g i v e n a d d i t i o n a l i s o c a l o r i c mash p r e s e n t a t i o n ( e x t i n c t i o n t r a i n i n g ) . EXTINCTION HIGH LOW CTl CO 44-MASH (g) 34-2 + i + 0 4 1 1 2 TRIAL 3 40 F i g u r e 7 - Mean c o n s u m p t i o n o f h i g h - a n d l o w - c a l o r i e mash whose f l a v o r s a r e r e v e r s e d by g e r b i l s g i v e n 3 a d d i t i o n a l d a y s mash p r e s e n t a t i o n . FLAVORS REVERSED 42 the p r i o r assoc iat ion formed from f l a v o r - c a l o r i e cond i t ion ing . Although g e r b i l s may use the information gained from f lavor -c a l o r i e condi t ioning when choosing betwen two i s o c a l o r i c d iets of d i f f erent f l avors , they do not re ly exc lus ive ly on taste cues when offered foods of d i f f erent c a l o r i c dens i ty . When given 3 a d d i t i o n a l days with no f lavors added to mash, gerb i l s exc lus ive ly consumed h i g h - c a l o r i e mash [ F (1,3)=292.2598, p_ =.0023]. G e r b i l s consumed a mean 3.72 g and 0.0 g of h igh- and low-ca lor ie mash, re spec t ive ly . Figure 8 i l l u s t r a t e s the strong avoidance of low-calor ie mash by g e r b i l s . This further demonstrates the g e r b i l s a b i l i t y to use cues other than taste when choosing the h i g h - c a l o r i e food i f presented with foods of d i f f eren t c a l o r i c density that have the same f lavor or e s s e n t i a l l y no f lavor as soc ia t ions . In add i t i on , the g e r b i l s ' a b i l i t y to choose a h i g h - c a l o r i e food does not appear to be affected by p r i o r f lavor assoc iat ions to that p a r t i c u l a r food. 43 F i g u r e 8 - Mean c o n s u m p t i o n o f h i g h - a n d l o w - c a l o r i e mash by g e r b i l s g i v e n 3 a d d i t i o n a l d a y s w i t h no f l a v o r s a d d e d t o mash. NO FLAVORS 5 j 4 3 •-MASH (g) 2-i 0<r-1 2 TRIAL HIGH LOW 45 I I I . EXPERIMENT 2 The p u r p o s e o f E x p e r i m e n t 2 was t o a n a l y z e t h e f o o d c h o i c e s o f t h e same h a m s t e r s and g e r b i l s a s i n E x p e r i m e n t 1 i n a f o r a g i n g s i t u a t i o n where t r a v e l i s n e c e s s a r y . T r a v e l i s an a d d i t i o n a l c o s t o f f o r a g i n g t h a t may a f f e c t d i e t s e l e c t i o n . We were i n t e r e s t e d i n d e t e c t i n g a c h a n g e i n p r e f e r e n c e f o r a known h i g h - c a l o r i e f o o d s o u r c e t h a t a s u b j e c t must now a c t i v e l y s e e k . S u b j e c t s were a l l o w e d t o f o r a g e on an 8-arm r a d i a l maze on w h i c h o n e - h a l f o f t h e arms were b a i t e d w i t h h i g h - c a l o r i e S u s t a c a l a n d o n e - h a l f w i t h l o w - c a l o r i e S u s t a c a l . E a c h s u b j e c t was a l l o w e d t o v i s i t a n d / o r d r i n k f r o m e i g h t a r m s . We were i n t e r e s t e d i n s e e i n g i f s u b j e c t s w o u l d p r e f e r t o v i s i t a n d d r i n k f r o m t h o s e arms w h i c h c o n t a i n e d t h e h i g h - c a l o r i e S u s t a c a l . I f f l a v o r -c a l o r i e a s s o c i a t i o n s a r e an i m p o r t a n t f a c t o r i n f o r a g i n g i n n a t u r a l s e t t i n g s , t h a n we w o u l d e x p e c t s u b j e c t s t o r e a d i l y l e a r n t o v i s i t p l a c e s c o n t a i n i n g t h e h i g h - c a l o r i e f o o d . 4.1 M e t h o d 4.1.1 S u b j e c t s The same h a m s t e r s a n d g e r b i l s t h a t s e r v e d a s s u b j e c t s i n E x p e r i m e n t 1 s e r v e d i n E x p e r i m e n t 2. 4.1.2 M a t e r i a l s D u r i n g t e s t i n g , s u b j e c t s were t r a n s p o r t e d i n t h e i r homecage f r o m t h e h o u s i n g room i n t o t h e t e s t i n g room. An 8-arm r a d i a l maze was e l e v a t e d (60cm) i n t h e c e n t e r o f a 3.2m x 2.8m x 2.8m t e s t i n g room. The d i m e n s i o n s o f e a c h arm were 30cm x 15.5cm and 46 the diameter of the center platform was 90cm. Each arm was f l a t and without wal l s . A small receptacle for food or l i q u i d was located at the d i s t a l end of each arm. Extramaze v i s u a l cues consisted of the fo l lowing: two swivel c h a i r s , a garbage can, a large wooden board (3.0m x 2.5m), six shelf doors, a countertop, and a door. No intramaze cues were provided. The experimenter sat in the same swivel chair in the same corner of the tes t ing room for each t r i a l . The high- and low-calor ie Sustacal was the same as in Experiment 1. 4.1.3 Procedure Hamsters were f i r s t reconditioned to the ir o r i g i n a l f l a v o r -c a l o r i e assoc ia t ions . Gerb i l s were condit ioned to a new f l a v o r -c a l o r i e assoc iat ion that used Sustacal l i q u i d as a diet mix rather than mash. Both species were presented with Sustacal l i q u i d in the same fashion as out l ined in Experiment 1, Part 2. Pr ior to the tes t ing phase, each subject was allowed to explore the unbaited maze for 5 consecutive days, 10 min each day. During subsequent test phases, Sustacal l i q u i d (1ml) was located in the recept ic l e at the end of each maze arm. For each subject , one-half of the arms contained h igh-c a l o r i e Sustacal and one-half contained low-calor ie Sustaca l . For each subject , h igh- and low-ca lor ie Sustacal f lavor associat ions remained the same as in Experiment 1. The assignment of each arm locat ion - Sus taca l - f lavor assoc iat ion was random for each subject and remained the same for each t r i a l . However, hamsters and g e r b i l s were randomly paired such 47 that a hamster foraging on a maze where arms #2, #4, #6, and #7 are h i g h - c a l o r i e v a n i l l a Sustacal i s matched to a g e r b i l foraging under the same cond i t ions . After being placed in the center of the maze, subjects were allowed to v i s i t a t o t a l of eight arms and drink the Sustacal l i q u i d . R e v i s i t i n g an arm was also considered as a v i s i t . Accordingly , a subject could v i s i t eight arms without entering a l l ava i l ab l e arms. Arm choice or a v i s i t was made when the subject ' s hind paws transversed the arm entrance. A drink was taken when the subject 's tongue entered the recept i c l e at least once. Many subjects sampled by taking a s ingle l i c k of Sus taca l . This was considered as dr inking in th i s context. Not d r i n k i n g , then, i s evident by the subject 's f a i l u r e to taste the l i q u i d . After eight choices were made the subjects were removed from the maze apparatus, and returned to the housing room. 4.1.4 S t a t i s t i c s Data for both hamsters and g e r b i l s were analyzed using the same s t a t i s t i c s . A within-group analys i s of variance with two f ixed fac tors , t r i a l and c a l o r i c density (high and low), was used when analyzing recondit ioning measures from hamsters and condit ioning measures from g e r b i l s . When the subjects v i s i t e d each arm on the maze, arm locat ion (number) and whether or not the subject drank from the arm was noted. The number of v i s i t s to the h igh -ca lor i e arm locat ions were t a l l i e d and div ided by the t o t a l number of 48 p o s s i b l e v i s i t s per t r i a l . If c o n s i d e r i n g the s u b j e c t s ' performance a f t e r four c h o i c e s , then the t o t a l number of v i s i t s i s f o u r . Thus, a subject who v i s i t e d one h i g h - c a l o r i e arm l o c a t i o n has v i s i t e d 25% of the p o s s i b l e h i g h - c a l o r i e arm l o c a t i o n s . To determine d r i n k i n g performance s u b j e c t s r e c e i v e d one p o i n t f o r e i t h e r d r i n k i n g from a h i g h - c a l o r i e arm l o c a t i o n or not d r i n k i n g from a l o w - c a l o r i e arm l o c a t i o n . T h i s method of s c o r i n g was necessary to c o n t r o l f o r s u b j e c t s who drank from a l l arms or no arms. These p o i n t s were t a l l i e d and d i v i d e d by the t o t a l number of p o s s i b l e v i s i t s per t r i a l . Subjects r e c e i v e d a t o t a l score f o r the number of v i s i t s to and d r i n k s from h i g h -c a l o r i e arm l o c a t i o n s . These scores were compared to chance l e v e l (50%) us i n g a t - t e s t s t a t i s t i c . P r e f e r e n c e r a t i n g s were a l s o o b t a i n e d f o r each s u b j e c t . Since s u b j e c t s c o u l d v i s i t e i g h t arms, a score of e i g h t i d e n t i f i e d the s u b j e c t s f i r s t c h o i c e , a h i g h l y p r e f e r r e d arm l o c a t i o n . The s u b j e c t s ' second c h o i c e r e c i e v e d a score of seven; the t h i r d c h o i c e r e c i e v e d a score of s i x ; f o u r t h c h o i c e i s f i v e ; and so on. Arms that were r e v i s t e d or not v i s i t e d r e c i e v e d a score of zero. For each t r i a l a preference r a t i n g score f o r each arm was obtained f o r each s u b j e c t . The pref e r e n c e scores were summed a c r o s s t r i a l s . Preference r a t i n g s allows us to d e p i c t a c o n s i s t e n t p r e f e r e n c e f o r one or more arms, response p a t t e r n i n g or c i r c l i n g , or a memory-based s t r a t e g y . An arm that i s p r e f e r r e d w i l l have a high preference s c o r e . A c i r c l i n g s t r a t e g y w i l l be evident i f the subject begins each 49 t r i a l in the same locat ion and c i r c l e s in the same d i r e c t i o n . If so, the graph i l l u s t r a t i n g preference score and arm locat ion w i l l have a peak marking the arm that begins the c i r c u i t and a progress ive ly lower preference rat ing for each arm locat ion fol lowing the peak. If the graph has no peaks and the subject has a high performance score, then the lack of response patterning may indicate that the subject used a memory-based strategy or that the subject began each t r i a l in a d i f f erent arm l o c a t i o n . 4.1.5 Results And Discussion For Experiment 2, eight hamsters were recondit ioned to the ir o r i g i n a l c a l o r i c density - Sus taca l - f lavor as soc ia t ion . After 5 condit ioning days, hamsters consumed more h i g h - c a l o r i e l i q u i d ( M =7.39 ml) than low-calor ie l i q u i d ( M =2.49 ml) [ F (1,7)=23.3512, g =.0023]. On the 8-arm r a d i a l maze where one-half of the arms were baited with h igh-ca lor i e Sustacal and one-half with low-ca lor ie Sustaca l , of the f i r s t four choices , 54% of the v i s i t s were to h igh -ca lor i e arm loca t ions . This was not above chance (50%) [ t (7) = .95, p_ =.3800]. Of the f i r s t four choices , 66% of the drinks were taken at h igh-ca lor i e arm loca t ions . This was above chance [ t (7)=3.8, g =.0089]. As shown in Figure 9, for a l l eight choices , 55% of the v i s i t s were to h igh-ca lor i e arm loca t ions . This was not above chance [ t (7) = 2.12, p_ =.0780]. For a l l eight choices , 72% of the drinks were taken at h igh-c a l o r i e arm locat ions (Figure 9). This was above chance [ t (7)=7.72, 2 =.0002]. Thus, hamsters d id not prefer to v i s i t the 50 F i g u r e 9 - The percentage of v i s i t s to and d r i n k s from arm l o c a t i o n s that c o n t a i n h i g h - c a l o r i e S u s t a c a l l i q u i d f o r both hamsters and g e r b i l s . HAMSTERS GERBILS 52 h i g h - c a l o r i e arm l o c a t i o n s . H o wever, t h e y d i d p r e f e r t o d r i n k f r o m t h e s e l o c a t i o n s . F i g u r e 10 d e p i c t s t h e arm p r e f e r e n c e r a t i n g f o r e a c h h a m s t e r . Arm p r e f e r e n c e i s c a l c u l a t e d by summing t h e p r e f e r e n c e r a t i n g f o r e a c h arm a c r o s s t r i a l s ( r e f e r t o t h e s t a t i s t i c s S e c . 4.1.4. f o r f u r t h e r d e t a i l s ) . A l t h o u g h e a c h h a m s t e r was r a n d o m l y a s s i g n e d d i f f e r e n t h i g h - c a l o r i e arm l o c a t i o n s , t h e y b e gan e a c h t r i a l a t t h e same arm ( v i z . arm #2), and c i r c l e d t h e maze i n t h e same d i r e c t i o n f o r e a c h t r i a l . I n F i g u r e 10, t h e h i g h - c a l o r i e arm l o c a t i o n s a r e g i v e n f o r e a c h s u b j e c t . E a c h arm p r e f e r e n c e g r a p h shows t h a t t h e s u b j e c t d i d n o t s e l e c t i v e l y v i s i t t h e h i g h - c a l o r i e arm l o c a t i o n s . H o w e v e r , i f t h e s e s u b j e c t s were c i r c l i n g t h e maze i n o r d e r t o l o c a t e h i g h - c a l o r i e a r m s , t h e n t h e o b s e r v e d 5 5 % o f v i s i t s t o h i g h - c a l o r i e arms i s n o t s u r p r i s i n g s i n c e 50% o f t h e arms c o n t a i n e d h i g h - c a l o r i e S u s t a c a l . T h e i r d e c i s i o n o f w h e t h e r o r n o t t o d r i n k f r o m an arm l o c a t i o n p r o v i d e s more i n f o r m a t i o n a b o u t t h e i r d i e t p r e f e r e n c e s . T h e i r f o r a g i n g s t r a t e g y , m a i n l y u s i n g an a l g o r i t h m , d i c t a t e s t h e i r arm l o c a t i o n p r e f e r e n c e s . T h a t i s , t h e arm w h i c h i s most p r e f e r r e d i s t h a t arm w h i c h i s n e x t t o t h e arm c u r r e n t l y v i s i t e d . F o r E x p e r i m e n t 2, e i g h t g e r b i l s were c o n d i t i o n e d t o p r e f e r h i g h - c a l o r i e S u s t a c a l l i q u i d u s i n g t a s t e c u e s . They consumed more h i g h - c a l o r i e l i q u i d ( M =6.18 ml) t h a n l o w - c a l o r i e l i q u i d ( M =0.58 ml) [ F (1 ,7) = 111.5731, p = . 0 0 0 1 ] . When f o r a g i n g on t h e 8-arm r a d i a l maze u n d e r t h e same c o n d i t i o n s a s t h e h a m s t e r s , o f t h e f i r s t f o u r c h o i c e s , 49% o f 53 F i g u r e 10 - The arm p r e f e r e n c e t o t a l s , p r e f e r e n c e v a l u e , summed a c r o s s t r i a l s f o r e a c h h a m s t e r v i s i t i n g h i g h - a n d l o w -c a l o r i e arm l o c a t i o n s on t h e 8-arm r a d i a l maze. The arms c o n t a i n i n g h i g h - c a l o r i e S u s t a c a l l i q u i d a r e n o t e d f o r e a c h s u b j e c t . 55 the v i s i t s were to h i g h - c a l o r i e arm loca t ions . This was not above chance (50%) [ t (7) = .20, p_ =.8500]. Of the f i r s t four choices , 56% of the drinks were taken at h i g h - c a l o r i e arm l o c a t i o n s . This was not above chance [ t (7) = .87, p_ =.4100], As shown in Figure 9, for a l l eight choices , 52% of the v i s i t s were to h i g h - c a l o r i e arm loca t ions . This was not above chance [ t (7)=1.02, 2 =.3400]. For a l l eight choices , 60% of the drinks were taken at h i g h - c a l o r i e arm locat ions (Figure 9). This was not above chance [ t (7)=1.55, 2 =.1600]. G e r b i l s , l i k e hamsters, d id not prefer to v i s i t the h i g h - c a l o r i e arm l o c a t i o n s . However, unl ike hamsters, gerb i l s d id not prefer to drink from h i g h - c a l o r i e arm loca t ions . Figure 11 depicts the arm preference rat ing for each g e r b i l . According to Figure 11, no arm was preferred across a l l t r i a l s , and no o v e r a l l c i r c l i n g strategy i s v i s i b l e . Thus, unl ike hamsters, gerb i l s d i d not adopt a foraging strategy in order to e i ther locate or consume food rewards. 56 F i g u r e 11 - The arm p r e f e r e n c e t o t a l s , p r e f e r e n c e v a l u e , summed a c r o s s t r i a l s f o r e a c h g e r b i l v i s i t i n g h i g h - a n d l o w -c a l o r i e arm l o c a t i o n s on t h e 8-arm r a d i a l maze. The arms c o n t a i n i n g h i g h - c a l o r i e S u s t a c a l l i q u i d a r e n o t e d f o r e a c h s u b j e c t . 58 IV. EXPERIMENT 3 The purpose of Experiment 3 was to compare the hamsters' performance i n a r a d i a l - a r m maze on which the arms were e q u a l l y b a i t e d to both t h e i r performance i n an unequally b a i t e d r a d i a l -arm maze as w e l l as to other s p e c i e s ' performance i n an e q u a l l y b a i t e d r a d i a l - a r m maze. Hamsters were p l a c e d on a 17-arm r a d i a l maze b a i t e d with s i n g l e sunflower seeds. In the f i r s t phase, the f o r a g i n g s t r a t e g y u t i l i z e d i n c o l l e c t i n g these seeds was noted. In the second phase, four of the b a i t e d arms were blocked. A f t e r the hamsters made 13 c h o i c e s , they were t e m p o r a r i l y removed from the maze, while the blocks were withdrawn. The hamsters' subsequent four c h o i c e s when returned to the maze were recorded. T h i s t e s t allowed the hamsters to demonstrate a memory-based s t r a t e g y f o r c o l l e c t i n g seeds i n a maze s i t u a t i o n . 5.1 Method 5.1.1 Subjects F i v e e x p e r i m e n t a l l y naive Golden hamsters (two female, three male) were housed i n d i v i d u a l l y i n opaque-sided cages i n a colony on a r e v e r s e d 12-hour l i g h t / 12-hour dark c y c l e (dark c y c l e began at 8:00am). They had u n l i m i t e d access to water and were maintained at 80% of t h e i r f r e e - f e e d i n g body weight. They were t e s t e d d u r i n g the l a s t t h i r d of the dark c y c l e . 59 5.1.2 Mater ia l s A 17-arm r a d i a l maze was c e n t r a l l y posi t ioned on the f loor in a 3.2m x 2.8m x 2.8m room. The dimensions of each arm were 60cm x 13cm x 14cm and the diameter of the center platform was 72cm. The top of each arm was covered by translucent p l a s t i c . The ent ire maze was painted gray. Extramaze v i s u a l cues consisted of the fo l lowing: three large posters (90cm x 60cm) and six small p ic tures (15cm x 15cm) attached to the walls about 1.5m above the f l o o r , scattered boxes, a garbage can, two c h a i r s , a door, six shelf doors, and a countertop. No intramaze cues were provided. Sunflower seeds were strewn around the outside of the maze to prevent the subjects from using food odors as cues as to whether or not a p a r t i c u l a r arm was ba i ted . 5.1.3 Procedure Pr ior to the tes t ing phases, each hamster was allowed to explore the unbaited maze for 7 consecutive days for approximately 30 min each day. During subsequent test phases, a s ingle sunflower seed was located in a small receptacle at the end of each maze arm. During Phase 1 (Day 1 to Day 14), each hamster was allowed access to the maze for 10 min or u n t i l 17 arms were v i s i t e d . A l l arm choices were recorded. An entry into an arm was defined as placement of a l l four paws within the arm - with or without seed removal. During Phase 2 (Day 15 to Day 25), the entrance to four randomly selected arms was blocked with wire mesh. After 13 arm choices , the hamster was placed 60 within i t s homecage, the blocks were removed, and the hamster was returned to the maze. The i n t e r v a l between removal and replacement of the subject was approximately 10 s. The f i r s t four choices after replacement were recorded. The purpose of Phase 2 was to invest igate the hamsters' use of a memory-based strategy for foraging. If a response strategy was being used to c o l l e c t the sunflower seeds, blocking a cer ta in number of arms would l i m i t the e f f i c i ency of th i s s trategy. Hamsters who successful ly v i s i t e d the previously blocked and s t i l l baited arms necessar i ly re ly on a memory-based foraging strategy. During Phase 1, the homecage was placed in the center of the maze. An inverted V-shape wire mesh ladder (15cm wide) that allowed the hamster to leave and reenter the cage was randomly placed in one of the four sides of the cage. Access to the homecage was provided so that the hamsters' could transport seeds back to i t s cache. Since th i s behavior was not observed, during Phase 2, only the ladder was placed in the center of the maze. Each hamster was placed on the top of the ladder at the beginning of each test session and when being returned to the maze in Phase 2. 5.1.4 S t a t i s t i c s Analys is of the hamsters' performance on the 17-arm equal ly -ba i ted r a d i a l maze involves accuracy scores, preference ra t ings , and patterning measures. Two types of accuracy scores are generated. The f i r s t accuracy score i s the number of correct v i s i t s ( i . e . , v i s i t i n g 61 b a i t e d arms) averaged a c r o s s a l l s u b j e c t s and r e p o r t e d f o r each t r i a l . T h i s i s accuracy a c r o s s t r i a l s . The second accuracy score i s the number of c o r r e c t v i s i t s averaged across t r i a l s r e p o r t e d f o r each arm c h o i c e . T h i s i s accuracy w i t h i n t r i a l s . P r e f e r e n c e r a t i n g s were ob t a i n e d i n the same f a s h i o n as o u t l i n e d i n Experiment 2 (Sec. 2.1.4). However, the highest p r e f e r e n c e score i s 17 s i n c e the maze c o n s i s t e d of 17 arm l o c a t i o n s . To look f o r p o s s i b l e response s t r a t e g i e s the number of c h o i c e s as a f u n c t i o n of the chosen arms p o s i t i o n r e l a t i v e to the l a s t c h o i c e was c a l c u l a t e d . Choosing the arm d i r e c t l y to the l e f t or r i g h t of the arm c u r r e n t l y v i s i t e d i s + or -1; choosing the arm two doors to the l e f t or r i g h t of the arm c u r r e n t l y v i s i t e d i s + or -2; three doors i s + or -3; and so on. 5.1.5 R e s u l t s And D i s c u s s i o n Each hamster q u i c k l y l e a r n e d to l o c a t e the sunflower seeds at the end of each maze arm. As shown i n F i g u r e 12, they r e t r i e v e d the seeds at accuracy l e v e l s comparable to that r e p o r t e d f o r r a t s , g e r b i l s , and mice. As shown i n F i g u r e 12, r a t s , hamster, and g e r b i l s performed above chance (64%). That i s , they v i s i t e d more b a i t e d arms than that number of b a i t e d arms that c o u l d have been v i s i t e d randomly. Chance performance was c a l c u l a t e d by Eckerman (1980). Eckerman c o n s i d e r s both the d i f f i c u l t y i n d i s c o v e r i n g b a i t e d arms as the number of v i s i t s i n c r e a s e s , and a p r e f e r e n c e f a c t o r determined by the subjects', past s e l e c t i o n p a t t e r n s when f o r a g i n g with a response b i a s . The chance of v i s i t i n g a b a i t e d arm on the f i r s t c h o i c e i s 100% 62 F i g u r e 12 - The p e r c e n t a g e o f v i s i t s t o b a i t e d arms f o r r a t s , g e r b i l s , h a m s t e r s , a n d m i c e . D a t a f o r r a t s f r o m O l t o n , C o l l i s o n , a n d W e r z , 1977 ; f o r g e r b i l s f r o m W i l k i e a n d S l o b i n , 1983 ; f o r m i c e f r o m M i z u m o r i , R o s e n z w e i g , a n d K e r m i s c h ; 1982. ACCURACY SPECIES 64 s i n c e a l l arms a r e b a i t e d . T h i s v a l u e c h a n g e s f o r e a c h arm s e l e c t e d t h e r e a f t e r a s a f u n c t i o n o f t h e number o f b a i t e d arms a v a i l a b l e t o t h e s u b j e c t a t e a c h s e l e c t i o n . The r e p o r t e d c h a n c e l e v e l o f 64% i s a c o m p o s i t e o f c h a n c e p e r f o r m a n c e c a l c u l a t e d f o r t h e p r o b a b i l i t y o f v i s i t i n g e a c h b a i t e d arm b a s e d upon t h e number o f b a i t e d arms a v a i l a b l e amd t h e r e s p o n s e b i a s e s o f t h e s u b j e c t . F i g u r e 13 d e p i c t s t h e p e r c e n t o f c o r r e c t ( i . e . , a s y e t u n v i s i t e d ) arm e n t r i e s , a v e r a g e d a c r o s s t h e f i v e h a m s t e r s f o r Day 1 t o Day 14 ( i . e . , a c c u r a c y a c r o s s t r i a l s ) . I n o r d e r t o i l l u s t r a t e t h e c o m p a r a b l e p e r f o r m a n c e o f h a m s t e r s , g e r b i l s , a n d r a t s on t h e 17-arm r a d i a l maze, p r e v i o u s l y p u b l i s h e d d a t a f r o m g e r b i l s ( W i l k i e & S l o b i n , 1983) and r a t s ( O l t o n , C o l l i s o n , & Werz, 1977) a r e a l s o shown. When u s i n g a r e s p o n s e s t r a t e g y t h e h a m s t e r s ' p e r f o r m a n c e was a s c o n s i s t e n t a s t h a t d e m o n s t r a t e d by r a t s a n d g e r b i l s t h a t p r e s u m a b l y c o l l e c t f o o d r e w a r d s f r o m t h e maze by u s i n g a memory-based s t r a t e g y . Arm p r e f e r e n c e r a t i n g s f o r h a m s t e r s ( F i g u r e 14) a n d r a t s ( O l t o n , C o l l i s o n , & Werz, 1977) ( F i g u r e 15) s u g g e s t t h a t no p a r t i c u l a r s e q u e n c e f o r v i s i t i n g arms n o r a p a r t i c u l a r arm was p r e f e r r e d a c r o s s t r i a l s . T h i s c o n t r a s t s t o t h a t d i s c o v e r e d f o r h a m s t e r s i n E x p e r i m e n t 2. However, when t h e number o f c h o i c e s a s a f u n c t i o n o f t h e c h o s e n arms p o s i t i o n s r e l a t i v e t o t h e l a s t c h o i c e i s e x a m i n e d , a t u r n i n g s t r a t e g y i s a p p a r e n t ( F i g u r e 1 6 ) . F o r e x a m p l e , c h o o s i n g t h e arm d i r e c t l y t o t h e l e f t o r r i g h t o f t h e arm c u r r e n t l y v i s i t e d i s + o r - 1; c h o o s i n g t h e arm two d o o r s t o t h e l e f t o r r i g h t o f t h e arm c u r r e n t l y v i s i t e d i s + o r 65 F i g u r e 13 - The p e r c e n t a g e o f v i s i t s t o b a i t e d arms f o r r a t s , g e r b i l s , a n d h a m s t e r s a v e r a g e d a c r o s s s u b j e c t s f o r e a c h t r i a l . D a t a f o r r a t s f r o m O l t o n , C o l l i s o n , a n d W e r z , 1977 ; f o r g e r b i l s f r o m W i l k i e a n d S l o b i n , 1983. 95-r % CORRECT 8o4-HAMSTERS GERBILS - r - RATS 67 F i g u r e 14 - The arm p r e f e r e n c e t o t a l s , p r e f e r e n c e v a l u e , summed a c r o s s t r i a l s f o r e a c h h a m s t e r v i s i t i n g arm l o c a t i o n s on t h e 17-arm r a d i a l maze. 69 F i g u r e 15 - The arm p r e f e r e n c e t o t a l s , p r e f e r e n c e v a l u e , summed a c r o s s t r i a l s f o r e a c h r a t v i s i t i n g arm l o c a t i o n s on t h e 17-arm r a d i a l maze. D a t a t a k e n f r o m O l t o n , C o l l i s o n , a n d Werz, 1 977. 71 F i g u r e 16 - The f r e q u e n c y o f v i s i t s a s a f u n c t i o n o f t h e arm l o c a t i o n s r e l a t i v e p o s i t i o n t o t h e p r e v i o u s v i s i t . D a t a f o r r a t s f r o m O l t o n , C o l l i s o n , and W e rz, 1977 ; f o r g e r b i l s f r o m W i l k i e a nd S l o b i n , 1983. 73 2; t h r e e d o o r s i s + o r - 3; a n d s o o n . T h u s , F i g u r e 16 shows t h a t h a m s t e r s c h o o s e a v e r y h i g h p e r c e n t a g e o f a d j a c e n t arms. G e r b i l s a n d r a t s , on t h e o t h e r h a n d , a r e much l e s s l i k e l y t o e n t e r a d j a c e n t a r m s . T h i s s u g g e s t s t h a t h a m s t e r s u s e a c i r c l i n g s t r a t e g y s i m i l a r t o t h a t n o t e d i n E x p e r i m e n t 2 when f o r a g i n g on an e q u a l l y b a i t e d maze. I n o r d e r t o e x a m i n e t h e p o s s i b i l i t y t h a t h a m s t e r s c o u l d s u c c e s s f u l l y c h o o s e n o n - a d j a c e n t b a i t e d arms when f o r c e d , a random 4 o f t h e 17 arms were b l o c k e d . T h u s , t h e f i r s t 13 c h o i c e s f o r c e d t h e h a m s t e r t o t r a n s v e r s e b l o c k e d e n t r a n c e s b r e a k i n g t h e r e s p o n s e a l g o r i t h m — a l w a y s t u r n l e f t o r r i g h t . The l a s t 4 c h o i c e s f o r c e d t h e h a m s t e r t o l o c a t e b a i t e d arms w h i c h were n o t a d j a c e n t . P r e s u m a b l y , i n f o r m a t i o n g r a n t e d by e x p l o r a t i o n o f t h e maze d u r i n g t h e f i r s t 13 c h o i c e s a b o u t t h e c o n d i t i o n o f e a c h arm ( i . e . , b a i t e d v s u n b a i t e d ) w o u l d be a c c e s s i b l e d u r i n g t h e l a s t 4 c h o i c e s . F i g u r e 17 c o m p a r e s t h e p e r c e n t o f c o r r e c t c h o i c e s when no arms were b l o c k e d ( u n b l o c k e d ) , a n d t h e p e r c e n t o f c o r r e c t c h o i c e s f o r 17 arms when 4 arms were b l o c k e d ( b l o c k e d ) . The g r a n d mean f o r t h e number o f b a i t e d arm l o c a t i o n s c h o s e n by h a m s t e r s i n t h e u n b l o c k e d a n d b l o c k e d c o n d i t i o n s i s 8 4 . 8 % and 74.4%, r e s p e c t i v e l y . No d i f f e r e n c e e x i s t e d b e t w e e n t h e g r a n d mean u n d e r t h e s e c o n d i t i o n s [ t ( 3 2 ) = 1 . 2 9 , p =.21 0 0 ] , However, p e r f o r m a n c e d e c r e a s e d r a p i d l y a f t e r t h e t e n t h c h o i c e i n t h e b l o c k e d c o n d i t i o n . I f we compare a c c u r a c y f o r t h e l a s t s e v e n c h o i c e s , t h e n a s i g n i f i c a n t d i f f e r e n c e b e t ween t h e u n b l o c k e d ( M =69%) a n d b l o c k e d ( M =44%) c o n d i t i o n s d o es r e s u l t 74 F i g u r e 17 - The p e r c e n t a g e o f c o r r e c t v i s i t s t o b a i t e d arms f o r e a c h c h o i c e a v e r a g e d a c r o s s s u b j e c t s i n t h e u n b l o c k e d a n d b l o c k e d c o n d i t i o n s . OH 1 1 1 1 1 1 I 1 1 1 1 1 1 1 I 1 1 2 3 4 5 6 7 6 9 10 11 12 13 14 18 16 17 CHOICE 76 [ t (12)=2 .83, 2 =.016]. The greatest d i f ference between the unblocked ( M =58.9%) and blocked ( M =31%) condit ions was found in the las t four choices [ t (6)=4.46, 2 =.0066]. Thus, hamsters do not appear to possess the a b i l i t y to use a memory-based foraging strategy for c o l l e c t i n g food rewards under these experimental condi t ions . Contrary to our expectations, no hamster transported seeds from the maze arms back to the c e n t r a l l y - l o c a t e d home cage. It i s not c lear yet why the subjects d id not transport the seeds. Had more food items been ava i lab le cheekpouching may have been observed. 77 V. GENERAL DISCUSSION H a m s t e r s a n d g e r b i l s , l i k e r a t s ( B o l l e s e t a l . , 1 9 8 1 ) , c a n i d e n t i f y f o o d q u a l i t y by u s i n g t a s t e c u e s . I n p a r t i c u l a r , t h e s e r o d e n t s p e c i e s show a f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t . R a t s a n d g e r b i l s show a r o b u s t e f f e c t . H a m s t e r s , on t h e o t h e r h a n d , a r e more l i k e l y t o c h o o s e f o o d s o f v a r y i n g q u a l i t y r e g a r d l e s s o f t h e i r k n o w l e d g e o f f l a v o r a s a m e d i a t i n g c u e t o c a l o r i c d e n s i t y . I n i t i a l l y , h a m s t e r s t h a t were p r e s e n t e d w i t h h i g h - and l o w -c a l o r i e mash d i d n o t d e m o n s t r a t e f l a v o r - c a l o r i e c o n d i t i o n i n g . When h a m s t e r s were s i m u l t a n e o u s l y p r e s e n t e d w i t h b o t h d i e t m a s h e s , t h e y p l a c e d b o t h mashes i n t h e i r c h e e k p o u c h e s . H a m s t e r s , u n l i k e r a t s and g e r b i l s , h a v e e x t e n s i v e c h e e k p o u c h e s t h a t a i d i n t r a n s p o r t i n g f o o d t o t h e c e n t r a l c a c h e . These c h e e k p o u c h e s a p p a r e n t l y h i n d e r e d t h e h a m s t e r s i n f o r m i n g a s i n g l e f l a v o r - c a l o r i e a s s o c i a t i o n . T h u s , i n o u r i n i t i a l e x p e r i m e n t a l t a s k , t h e h a m s t e r s ' c h e e k p o u c h was a b i o l o g i c a l c o n s t r a i n t , i n p a r t i c u l a r , a m o r p h o l o g i c a l c o n s t r a i n t ( c f . Domjan & G a l e f , 1983; H i n d e & S t e v e n s o n - H i n d e , 1973; S h e t t l e w o r t h , 1 9 8 2 ) . The c h e e k p o u c h a s a b i o l o g i c a l c o n s t r a i n t i n d i e t s e l e c t i o n i s an i m p o r t a n t c o n s i d e r a t i o n . A c h e e k p o u c h e n a b l e s a f o r a g e r t o t r a n s p o r t l a r g e q u a n t i t i e s o f f o o d t o a c e n t r a l n e s t . T h u s , h a m s t e r s c a n h a r v e s t f o o d a n d b u i l d h o a r d s . I n d e e d t h e h a m s t e r s ' u s e o f a r e s p o n s e s t r a t e g y when f o r a g i n g on t h e r a d i a l - a r m maze may r e f l e c t a h a r v e s t i n g p a t t e r n . W i t h c h e e k p o u c h e s , a h a r v e s t e r may h a p h a z a r d l y c o l l e c t s e e d s t h a t a r e s t r a i n e d t h r o u g h a s e l e c t i o n p r o c e s s a f t e r a f o r a g i n g b o u t . 78 T h i s t y p e o f f o r a g i n g s u g g e s t s t h a t t h e h a m s t e r may be a d e l a y e d - d e c i s i o n m aker. I n a n a t u r a l s e t t i n g , c e n t r a l p l a c e f o r a g e r s who have i n t e n s e p r e d a t i o n p r e s s u r e may b e n e f i t by d e l a y i n g d i e t s e l e c t i o n u n t i l t h e r i s k o f p r e d a t i o n i s d e c r e a s e d . W h i l e f o r a g i n g , h a m s t e r s may l o a d t h e i r c h e e k p o u c h e s q u i c k l y a n d n o n s e l e c t i v e l y . T h i s d e c r e a s e s t h e i r p r e d a t i o n r i s k by e c o n o m i z i n g t h e amount o f t i m e s p e n t away f r o m c o v e r i n o r d e r t o f o r a g e . L i m a and V a l o n e ( 1 986) h a v e shown t h a t g r e y s q u i r r e l s ( S c i u r u s c a r o l i n e n s i s ) w h i c h a r e c e n t r a l p l a c e f o r a g e r s w i l l a l t e r l o a d s i z e when f o r a g i n g u n d e r v a r i o u s c o v e r d e n s i t i e s . K o t l e r ( 1 9 8 4 ) s u g g e s t s t h a t t h e f o r a g i n g b e h a v i o r o f g r a n i v o r o u s d e s e r t r o d e n t s i s a l s o r e s p o n s i v e t o b o t h p r e d a t i o n r i s k a n d f o o d r e s o u r c e s . A c c o r d i n g l y , h a m s t e r s t h a t f o r a g e i n b a r r e n d e s e r t c l i m a t e s may h a v e c h e e k p o u c h e s i n o r d e r t o s a f e l y t r a n s p o r t l a r g e q u a n t i t i e s o f f o o d l o n g d i s t a n c e s i n s p a r s e l y c o v e r e d a r e a s . T h u s , c h e e k p o u c h i n g a b i l i t i e s i n c r e a s e f o r a g i n g e f f i c i e n c y . However, i n c e r t a i n d i e t s e l e c t i o n t a s k s , t h e y may be c o n s i d e r e d a b i o l o g i c a l c o n s t r a i n t . C h e e k p o u c h l o a d i n g i s a d v a n t a g e o u s t o a h i g h l y - p r e d a t e d g e n e r a l i s t f e e d e r . H o w e v e r , i f c h e e k p o u c h e s were s e n s i t i v e t o t o x i n s o r f l a v o r s , t h e n t h e l o a d i n g p r o c e s s may become i n e f f i c i e n t . F o r p r e s u m a b l y , a h a m s t e r d i s c a r d s u n w a n t e d f o o d s , s u c h a s p o i s o n o u s o r d e c a y i n g i t e m s , a f t e r r e t u r n i n g t o i t s b u r r o w . I f t h e h a m s t e r h a s t o n o t e t h e f l a v o r o f a f o o d w h i l e h a r v e s t i n g , t h e n t h e p r o c e s s o f c h e e k p o u c h i n g s l o w s down t h e f o r a g i n g p r o c e s s . T h e r e f o r e , i n o u r i n i t i a l e x p e r i m e n t a l 79 s i t u a t i o n h a m s t e r s may h a v e been u n a b l e t o f o r m a s i n g l e f l a v o r -c a l o r i e a s s o c i a t i o n when c h e e k p o u c h i n g was p o s s i b l e . The i n t r o d u c t i o n o f l i q u i d d i e t s f o r c e d h a m s t e r s t o t a s t e e a c h f o o d . A t t h i s t i m e , t h e f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t was e v i d e n c e d . G e r b i l s , w h i c h do n o t h a v e c h e e k p o u c h e s , n e c e s s a r i l y t a s t e f o o d t h a t t h e y t r a n s p o r t t o t h e i r h o m e s i t e o r b u r r o w . The d i f f e r e n c e b e t w e e n h a m s t e r s a n d g e r b i l s i n h o a r d i n g s t r a t e g y was c l e a r i n o u r e x p e r i m e n t s . H a m s t e r s l o a d e d t h e i r c h e e k p o u c h e s and t r a n s p o r t e d t h e c h e e k p o u c h c o n t e n t s t o t h e c o r n e r o f t h e c a g e where t h e y c a c h e t h e i r f o o d . G e r b i l s a t t e m p t e d t o move t h e f o o d c u p s b u t o t h e r w i s e a t e t h e mash d i r e c t l y f r o m t h e c u p . S i n c e g e r b i l s c o u l d n o t t r a n s p o r t t h e mash, t h e i r i m m e d i a t e c o n c e r n may h a v e been f o o d q u a l i t y . G e r b i l s may n o t be d e l a y e d -d e c i s i o n m a k e r s . I f t h i s i s t h e c a s e , t h e n t h e g e r b i l s i n c r e a s e d s e n s i t i v i t y t o t a s t e c u e s o v e r t h a t o f t h e h a m s t e r s i s n o t s u r p r i s i n g . The f l a v o r use d i f f e r e n c e b e t w e e n h a m s t e r s and g e r b i l s i s f u r t h e r s t r e n g t h e n e d when we c o n s i d e r t h e e x t i n c t i o n e f f e c t s o f t h e t e s t p h a s e . H a m s t e r s , w h i c h r e q u i r e d l i q u i d p r e s e n t a t i o n t o a v o i d c h e e k p o u c h e f f e c t s , were more l i k e l y t o c h o o s e e i t h e r o f t h e i s o c a l o r i c l i q u i d s whose f l a v o r s were p r e v i o u s l y p a i r e d t o h i g h - o r l o w - c a l o r i e S u s t a c a l . T h e i r p r e f e r e n c e f o r a p a r t i c u l a r f l a v o r was n o t t e n a c i o u s . G e r b i l s , h o w e v e r , c o n t i n u e d t o p r e f e r t h e f l a v o r t h a t was p r e v i o u s l y p a i r e d t o t h e h i g h - c a l o r i e mash. G e r b i l s a p p e a r t o m a i n t a i n a s t r o n g e r f l a v o r a s s o c i a t i o n t h a n do h a m s t e r s . 80 G e r b i l s a p p a r e n t l y u s e c u e s o t h e r t h a n t a s t e when c h o o s i n g t h e h i g h - c a l o r i e mash. I n t h e f l a v o r s r e v e r s e d a n d no f l a v o r s c o n d i t i o n , no l o w - c a l o r i e mash was consumed. A n o t h e r s e n s o r y c u e , w h i c h B o l l e s e t a l . ( 1 9 8 1 ) s u g g e s t e d t h a t r a t s may have u s e d , i s t e x t u r e c u e s . The l o w - c a l o r i e mash c o n t a i n e d a l p h a -c e l l u l o s e w h i c h i s a n o n - c a l o r i c f i b e r . T h u s , t h e l o w - c a l o r i e mash may ha v e h a d a s o f t e r o r d r i e r t e x t u r e . When t h e d i e t s were m i x e d b o t h i s o c a l o r i e mashes n e c e s s a r i l y h a d t h e same t e x t u r e . T h e r e f o r e , g e r b i l s r e l i e d upon t a s t e c u e s . Of c o u r s e , g e r b i l s a l s o d e m o n s t r a t e d t h e f l a v o r - c a l o r i e c o n d i t i o n i n g e f f e c t when p r e s e n t e d w i t h S u s t a c a l l i q u i d . T h u s , t h e y do n o t r e l y e x c l u s i v e l y on t e x t u r e c u e s , b u t may a l s o u s e t a s t e c u e s . H a m s t e r s a n d g e r b i l s t h a t consumed S u s t a c a l l i q u i d c o u l d n o t use t e x t u r e c u e s s i n c e b o t h t h e d i e t m i x e s were w a t e r e d down t o d i f f e r e n t c o n s i s t e n c i e s ; no a d d i t i v e s were e m p l o y e d . An i n t e r e s t i n g q u e s t i o n i n t h e f l a v o r - c a l o r i e c o n d i t i o n i n g p a r a d i g m i n v o l v e s t h e r o d e n t s ' a b i l i t y t o d e t e c t c a l o r i c d e n s i t y g i v e n t h e same f l a v o r . When g i v e n two f o o d s w i t h t h e same f l a v o r b u t d i f f e r e n t c a l o r i c d e n s i t i e s w i l l r o d e n t s be a b l e t o d e t e c t c a l o r i c d e n s i t y , a n d p r e f e r t h e h i g h e r q u a l i t y f o o d i t e m ? O r , w i l l t h e s w e e t n e s s o f b o t h s o l u t i o n s i n h i b i t r o d e n t s ' f r o m i d e n t i f y i n g t h e h i g h - c a l o r i e f o o d i t e m . We've l a b e l l e d t h i s t h e " N u t r i s w e e t d i l e m n a " . F o r e x a m p l e , i f r a t s a r e p r e s e n t e d w i t h c h e r r y K o o l - a i d t h a t i s s w e e t e n e d w i t h N u t r i s w e e t a n d c h e r r y K o o l - a i d t h a t i s s w e e t e n e d w i t h s u g a r , t h e n w h i c h K o o l - a i d d r i n k w i l l t h e y p r e f e r ? T h i s a p p r o a c h a s k s i f t h e amount o f s u g a r i n a f o o d i t e m c a n be d e t e c t e d w i t h o u t t a s t e o r t e x t u r e c u e s . T h i s 81 a p p r o a c h c o u l d a l s o be u s e d t o e x p l o r e t h e r o d e n t s ' s e n s i t i v i t y t o f o o d i t e m s w i t h e x c e s s i v e s u g a r . Can a f o o d h a v e t o o many c a l o r i e s o r be t o o s w e e t ? I n t e r e s t i n g l y , we assume t h a t s i n c e a n i m a l s h a v e an i n n a t e p r e f e r e n c e f o r s w eet f o o d s t h a t t h e y w i l l a l w a y s c h o o s e f o o d i t e m s w i t h t h e h i g h e s t s u g a r c o n t e n t ( R o z i n , 1 9 7 7 ) . P e r h a p s , t h i s a s s u m p t i o n i s f a u l t y . As m e n t i o n e d e a r l i e r , a n i m a l s c a n e a t t o o much o f a 'good' f o o d . S i n c e a n i m a l s must g a t h e r n u t r i e n t s i n a d d i t i o n t o c a l o r i e s , f o o d - s e a r c h b e h a v i o r s w h i c h r e l y e x c l u s i v e l y on c a l o r i c i n p u t may be m a l a d a p t i v e . The e n e r g y m a x i m i z i n g m o d el o f OFT a s sumes t h a t o p t i m a l e q u a t e s t o 'most'. T h u s , i f e n e r g y i s d e f i n e d i n t e r m s o f c a l o r i c u n i t s , t h e n f o r a g e r s must e a t t h e most amount o f c a l o r i e s i n o r d e r t o a p p e a r a s o p t i m a l f o r a g e r s . H owever, t h e 'most' amount o f s u g a r , f o r e x a m p l e , t h a t an a n i m a l c a n i n g e s t may be h a r m f u l . A l t h o u g h t h e body c a n s t o r e f o o d i n t h e f o r m o f f a t , an o v e r w e i g h t f o r a g e r i s a t a d i s a d v a n t a g e f o r two r e a s o n s . F i r s t , t h e i r b o d i e s a r e u n n e c e s s a r i l y t a x e d . S e c o n d , o v e r w e i g h t f o r a g e r s c a n n o t f l e e f r o m p r e d a t o r s a s q u i c k l y a s f i t a n i m a l s . I n l i g h t o f t h e s e d i s a d v a n t a g e s f o r u n f i t f o r a g e r s , p e r h a p s t h e d e f i n i t i o n o f an o p t i m a l f o r a g e r s h o u l d n o t be t h e a n i m a l who c o l l e c t s t h e 'most' e n e r g y i n t e r m s o f c a l o r i c u n i t s . When we assume i n OFT t h a t a n i m a l s h a v e no n u t r i t i o n a l c o n s t r a i n t s , p e r f e c t k n o w l e d g e o f f o o d q u a l i t y a n d o f t r a d e o f f s w i t h o t h e r k i n d s o f c o s t s o r b e n e f i t s ( K r e b s , S t e p h e n s , & S u t h e r l a n d , 1 9 8 3 ) , we may n o t be a s m i s t a k e n a s when we assume o p t i m a l i s t h e 'most'. I n d e e d , i n o u r d e m o n s t r a t i o n h a m s t e r s 82 a n d g e r b i l s d i d ha v e k n o w l e d g e o f f o o d q u a l i t y . H o wever, when a c t i v e l y f o r a g i n g t h e y d i d n o t se e k t o m a x i m i z e e n e r g y i n t a k e i n t h e same manner a s d e f i n e d by OFT. A l t h o u g h we s t r e s s t h a t h i g h s u g a r o r c a l o r i c i n t a k e i s u n h e a l t h y f o r humans, we e x p e c t h e a l t h y o r f i t non-human a n i m a l s t o d e m o n s t r a t e h i g h s u g a r o r c a l o r i c i n t a k e . The k e y w o r d s m e n t i o n e d i n t h e i n t r o d u c t i o n a r e ' p r o p e r d i e t ' . R o d e n t s may have k n o w l e d g e o f p r o p e r d i e t r e q u i r e m e n t s a n d s e l e c t f o o d s a c c o r d i n g t o t h e i r n u t r i t i o n a l n e e d s . A c c o r d i n g t o ' c a f e t e r i a ' d a t a , h e a l t h y r a t s c a n s e l f -s e l e c t a b a l a n c e d d i e t ( L a t , 1967; R i c h t e r , 1 942-1943, 1955; R o z i n , 1 9 6 8 ) . E x p e r i m e n t e r s , on t h e o t h e r h a n d , may n o t have k n o w l e d g e o f t h e r o d e n t s i m m e d i a t e d i e t a r y n e e d s a n d s e t a s a premium e x t r e m e a n d e x o r b i t a n t n u t r i t i o n a l g o a l s f o r t h e r o d e n t . The f e e d i n g s t r a t e g i e s a d o p t e d by r o d e n t s i n o r d e r t o m a i n t a i n , a p r o p e r d i e t may be s h a p e d by f o o d a v a i l a b i l i t y . A r o d e n t t h a t c a n h o a r d may r e a c t d i f f e r e n t l y t o s c a r c e f o o d . Wong ( 1 9 8 6 ) s u g g e s t s t h a t h a m s t e r s a n d g e r b i l s t h a t h a v e been f o o d d e p r i v e d may ha v e d i f f e r e n t f e e d i n g s t r a t e g i e s . A c c o r d i n g t o Wong, h a m s t e r s w i l l n o t e n h a n c e f o o d i n t a k e when d e p r i v e d . T h a t i s , t h e y m a i n t a i n t h e same o v e r a l l c a l o r i c i n p u t p e r d a y . G e r b i l s , h o w e v e r , i n c r e a s e f o o d i n t a k e when d e p r i v e d . I n o u r 8-arm r a d i a l maze s i t u a t i o n h a m s t e r s v i s i t e d a l l f o o d l o c a t i o n s , b u t p r e f e r r e d t o d r i n k f r o m t h e h i g h - c a l o r i e arm l o c a t i o n s . G e r b i l s , on t h e o t h e r h a n d , seemed t o r a n d o m l y s e l e c t arm l o c a t i o n s a n d were more w i l l i n g t o d r i n k f r o m e i t h e r h i g h - o r l o w - c a l o r i e arm l o c a t i o n s . S i n c e b o t h r o d e n t s were d e p r i v e d , p e r h a p s , d e p r i v a t i o n s t a t e h a d d i f f e r e n t i a l e f f e c t s on h o a r d e r s 83 ( i . e . , h a m s t e r s ) a n d n o n - h o a r d e r s ( i . e . , g e r b i l s ) . T h i s s h o u l d be f u r t h e r e x p l o r e d by i n t r o d u c i n g a n o n - d e p r i v e d g r o u p o f h a m s t e r s a n d g e r b i l s i n t o t h e same e x p e r i m e n t a l s i t u a t i o n o u t l i n e d i n E x p e r i m e n t 2. B a t s o n e t a l . s ' ( 1 9 8 1) d e s c r i p t i o n o f t h e r a t s ' b e h a v i o r when f o r a g i n g on a r a d i a l - a r m maze f o r a s i n g l e c h o c o l a t e m i l k r e w a r d p r o v i d e s an e x a m p l e o f . t h e r o d e n t s ' c h a n g e i n f o r a g i n g b e h a v i o r when f o o d a n d / o r w a t e r d e p r i v e d . They a p p e a r t o c h o o s e f o o d s w h i c h a r e n e e d e d a n d t o a v o i d u n n e c e s s a r y f o o d s . When t h i r s t y r a t s were p l a c e d on an 8-arm r a d i a l maze w i t h s e v e n arms b a i t e d w i t h w a t e r a n d one arm b a i t e d w i t h c h o c o l a t e m i l k . T h e i r p r e f e r e n c e f o r t h e c h o c o l a t e - b a i t e d arm d i d n o t c h a n g e . H o w e v e r , when f o o d a n d w a t e r d e p r i v e d t h e r a t s ' p r e f e r e n c e f o r t h e c h o c o l a t e - b a i t e d arm i n c r e a s e d . T h u s , t o a t h i r s t y r a t , t h e f o o d r e w a r d was u n n e c e s s a r y . The r a t s t h a t h a d k n o w l e d g e o f t h e f o o d q u a l i t y - l o c a t i o n a s s o c i a t i o n u s e d t h i s i n f o r m a t i o n o n l y when n e c e s s a r y . R a d i a l arm maze t a s k s h a v e been u s e d e x t e n s i v e l y t o e x p l o r e r o d e n t f o r a g i n g s t r a t e g i e s ( M i z u m o r i , R o s e n z w e i g , & K e r m i s c h , 1982; O l t o n , C o l l i s o n , & W e r z , 1977; W i l k i e & S l o b i n , 1 9 8 3 ) . R a d i a l - a r m mazes o f f e r a u n i q u e o p p o r t u n i t y t o i n v e s t i g a t e t h e r o l e o f d i e t s e l e c t i o n i n f o r a g i n g t a s k s u n d e r a c o n t r o l l e d e x p e r i m e n t a l s i t u a t i o n . A c c o r d i n g t o t h i s t h e s i s r e s e a r c h , t h e r o d e n t s ' a b i l i t y t o c h o o s e f o o d s t h a t p r o v i d e a d e q u a t e n u t r i e n t s i n a c h o i c e t a s k may a c t u a l l y t e l l u s v e r y l i t t l e a b o u t d i e t s e l e c t i o n i n an a c t i v e f o r a g i n g s i t u a t i o n . N e i t h e r h a m s t e r s n o r g e r b i l s i n o u r e x p e r i m e n t a l s e t t i n g s o u g h t f o o d i n a manner i n 84 w h i c h t h e o b s e r v e r c o u l d i d e n t i f y t h e f o r a g e r s ' k n o w l e d g e o f f o o d q u a l i t y . A c c o r d i n g t o o u r r e s u l t s f r o m E x p e r i m e n t 1, h a m s t e r s a n d g e r b i l s knew w h i c h f l a v o r r e p r e s e n t e d t h e h i g h -c a l o r i e f o o d . However, when v i s i t i n g f o o d l o c a t i o n s t h i s k n o w l e d g e was n o t d e m o n s t r a t e d . P e r h a p s , i n an a c t u a l f o r a g i n g s i t u a t i o n where t r a v e l i n c r e a s e s c o s t a l a r g e r d i f f e r e n c e i n f o o d q u a l i t y i s n e c e s s a r y b e f o r e t h i s k n o w l e d g e i s d e m o n s t r a t e d . F u t u r e r e s e a r c h s h o u l d e x p l o r e t h e r o d e n t s ' arm c h o i c e s g i v e n h i g h l y d i f f e r e n t f o o d q u a l i t y - f l a v o r a s s o c i a t i o n s ( e . g . , low d e n s i t y c o n t a i n s 20% o f t h e c a l o r i e s f o u n d i n t h e h i g h d e n s i t y d i e t ) . I n a d d i t i o n , f u t u r e r e s e a r c h s h o u l d i n v e s t i g a t e t h e r a t s ' p e r f o r m a n c e i n a s i m i l a r maze s i t u a t i o n a s u s e d i n E x p e r i m e n t 2. R e c a l l t h a t M i z u m o r i e t a l . (1982) s u g g e s t e d t h a t t h e r a d i a l - a r m maze s i t u a t i o n may t e l l u s v e r y l i t t l e a b o u t r o d e n t s ' f o o d - s e a r c h i n g s t r a t e g i e s . T h i s s t a t e m e n t was p a r t i a l l y b a s e d on t h e o b s e r v a t i o n t h a t m i c e r a n t h r o u g h t h e maze a t a much q u i c k e r p a c e t h a n r a t s . P e r h a p s , M i z u m o r i e t a l . ' s c o n t e n t i o n i s c o r r e c t when we a t t e m p t t o compare s p e c i e s ' p e r f o r m a n c e . I n d e e d , i n o u r e x p e r i m e n t s , t h e maze p e r f o r m a n c e o f h a m s t e r s may have d i f f e r e d f r o m g e r b i l s due t o a f o r a g i n g c o n s t r a i n t , s u c h a s l o c o m o t i o n , t h a t d o e s n o t a f f e c t d i e t s e l e c t i o n . F o r e x a m p l e , h a m s t e r s have q u a d r a p e d a l l o c o m o t i o n t h a t a i d s i n c l i m b i n g and m a n e u v e r i n g i n b u s h e s w h i c h y i e l d s e e d s t h a t a r e s p a t i a l l y more p r e d i c t a b l e b u t l e s s d e n s e ( R o s e n z w e i g , S m i g e l , & K r a f t , 1975; R e i c h m a n & O b e r s t e i n , 1 9 7 7 ) . Q u a d r a p e d a l l o c o m o t i o n a l l o w s h a m s t e r s t o h a r v e s t s c a t t e r e d s e e d s more e f f i c i e n t l y ( K o t l e r , 85 1 9 8 4 ) . G e r b i l s , on t h e o t h e r h a n d , a r e b i p e d a l a n d s a l t a t o r i a l . T h e i r b i p e d a l l o c o m o t i o n a l l o w s them b o t h t o e x p l o i t l a r g e , s c a t t e r e d c l u m p s o f s e e d s e f f i c i e n t l y a n d t o e s c a p e p r e d a t o r s q u i c k l y ( K o t l e r , 1 9 8 4 ) . As w e l l , g e r b i l s h a v e e n l a r g e d a u d i t o r y b u l l a e a n d m a s t o i d s t h a t a l l o w s them t o d e t e c t a n d e s c a p e p r e d a t o r s b e t t e r t h a n h a m s t e r s w h i c h do n o t h a v e e n l a r g e d b u l l a e . T h u s , on t h e same r a d i a l arm maze a p p a r a t u s , h a m s t e r s a n d g e r b i l s may h a v e a p r e d i s p o s i t i o n t o move f r o m arm t o arm d i f f e r e n t l y . G e r b i l s t h a t u s e b i p e d a l l o c o m o t i o n hop l o n g d i s t a n c e s q u i c k l y . H a m s t e r s t h a t u se q u a d r a p e d a l l o c o m o t i o n s c u r r y f r o m arm t o arm s u r v e y i n g e a c h p o s s i b l e f o o d l o c a t i o n i n a h a r v e s t i n g f a s h i o n . L o c o m o t i o n d i f f e r e n c e s b e t w e e n s p e c i e s , a s m e n t i o n e d by M i z u m o r i e t a l . ( 1 9 8 2 ) , may a f f e c t t h e o b s e r v e d f o r a g i n g s t r a t e g y on a r a d i a l - a r m maze a n d s h o u l d t h e r e f o r e be f u r t h e r e x p l o r e d . H a m s t e r s d i d n o t a l t e r t h e i r f o r a g i n g s t r a t e g y on a l a r g e r maze. When h a m s t e r s f o r a g e d on t h e e q u a l l y b a i t e d maze, t h e y r e l i e d e x c l u s i v e l y on a r e s p o n s e o r c i r c l i n g s t r a t e g y i n o r d e r t o c o l l e c t f o o d r e w a r d s f r o m t h e r a d i a l -arm maze. A l t h o u g h r a t s h a v e been known t o u s e a r e s p o n s e s t r a t e g y t o c o l l e c t f o o d r e w a r d s f r o m a r a d i a l - a r m maze ( F o r e m a n , 1 9 8 5 ) , t h e y a l s o c a n l o c a t e f o o d r e w a r d s by u s i n g a memory-based s t r a t e g y ( c f . O l t o n , 1978; R o b e r t s , 1 9 8 4 ) . R a t s c o l l e c t a h i g h number o f f o o d r e w a r d s f r o m t h e maze e v e n when i n t e r r u p t e d by b l o c k e d arm l o c a t i o n s o r t i m e - o u t s e s s i o n s d u r i n g w h i c h t h e y a r e removed f r o m t h e maze a p p a r a t u s . H a m s t e r s ' p e r f o r m a n c e d e c r e a s e d o n c e t h e a l g o r i t h m was d i s r u p t e d by b l o c k i n g arm l o c a t i o n s s u g g e s t i n g 86 t h a t t h e y c o n t i n u e d t o u s e a now i n e f f i c i e n t h a r v e s t i n g s t r a t e g y t o c o l l e c t s e e d s . H a m s t e r s u s e d t h e same r e s p o n s e s t r a t e g y o f v i s i t i n g c o n s e c u t i v e arms b o t h on t h e 8- a n d 17-arm r a d i a l maze. How e v e r , on t h e s m a l l e r maze e a c h h a m s t e r began e a c h t r i a l i n t h e same arm a n d c i r c l e d t h e maze i n t h e same d i r e c t i o n . T h i s i s i n t e r e s t i n g f o r two r e a s o n s . F i r s t , t h e h a m s t e r s were r a n d o m l y p l a c e d i n t h e c e n t e r o f b o t h mazes; t h e e x p e r i m e n t e r d i d n o t f a c e t h e h a m s t e r s t o w a r d s any p a r t i c u l a r arm a t t h e s t a r t o f t h e t r i a l . S e c o n d , e a c h h a m s t e r was a s s i g n e d d i f f e r e n t arms a s h i g h - c a l o r i e S u s t a c a l l i q u i d l o c a t i o n s . T h i s s u g g e s t s t h a t h a m s t e r s may u t i l i z e a memory-based s t r a t e g y when d e c i d i n g where t o b e g i n f o r a g i n g . L e g e r , O w i n g s , and C o s s ( 1 9 8 3 ) s u g g e s t t h a t f o r a g e r s , s u c h a s g r o u n d s q u i r r e l s , w i l l u s e m i c r o h a b i t a t c u e s a s m a r k e r s t o i n i t i a t e p a r t i c u l a r b e h a v i o r s i n c l u d i n g f o r a g i n g . A c c o r d i n g t o P o u c e t , C h a p u i s , D u r u p , a n d T h i n u s - B l a n c ( 1 9 8 6 ) , h a m s t e r s do b u i l d a r e p r e s e n t a t i o n o f t h e e n v i r o n m e n t b a s e d on t o p o l o g i c a l r e l a t i o n s b e t w e e n o b j e c t s , t h e o v e r a l l g e o m e t r i c s t r u c t u r e p r o v i d e d by t h e a r r a n g e m e n t o f o b j e c t s , a nd t h e r e l a t i o n s b e t w e e n o b j e c t s a n d e x t r a - a p p a r a t u s l a n d m a r k s . P e r h a p s , a p a r t i c u l a r l a n d m a r k was s a l i e n t t o a l l h a m s t e r s i n E x p e r i m e n t 2. The r o l e o f h a b i t a t o r e n v i r o n m e n t a l c u e s i n i n i t i a t i n g f o o d - s e a r c h i n g b e h a v i o r s i n h a m s t e r s s h o u l d be f u r t h e r e x p l o r e d . I n t h i s s e r i e s o f e x p e r i m e n t s , g e r b i l s ' maze p e r f o r m a c e p r e s e n t s an u n u s u a l c a s e . G e r b i l s h a v e shown t h e i r a b i l i t y t o u s e a memory-based s t r a t e g y t o c o l l e c t f o o d r e w a r d s f r o m t h e 87 r a d i a l - a r m maze ( W i l k i e & S l o b i n , 1 9 8 3 ) . B u t u n d e r t h e e x p e r i m e n t a l c o n d i t i o n s o u t l i n e d i n t h i s t h e s i s r e s e a r c h , g e r b i l s d i d n o t a d o p t a d e f i n i t i v e s t r a t e g y f o r v i s i t i n g arm l o c a t i o n s . P e r h a p s , t h e c h a n g e i n f o o d r e w a r d f r o m an e q u a l l y b a i t e d r a d i a l - a r m maze ( W i l k i e & S l o b i n , 1983) t o o u r u n e q u a l l y b a i t e d r a d i a l - a r m maze a f f e c t e d t h e g e r b i l s f o r a g i n g s t r a t e g y o r p e r h a p s t h e l a r g e r maze a l l o w s a b i p e d a l r o d e n t t o f o r a g e more e f f i c i e n t l y . I n a d d i t i o n , o u r u n e q u a l l y b a i t e d maze p r o v i d e d g r e a t e r c a l o r i c i n p u t p e r t r i a l t h a n d i d t h e s i n g l e 45-mg N o y e s f o o d p e l l e t s ( W i l k i e & S l o b i n , 1983) o f f e r e d on t h e e q u a l l y b a i t e d maze. A g a i n , i t w o u l d be i n t e r e s t i n g t o e x p l o r e t h e e f f e c t s o f i n c r e a s e d q u a l i t y d i f f e r e n c e s on t h e g e r b i l s ' f o r a g i n g p e r f o r m a n c e on t h e r a d i a l - a r m maze. I n c o n c l u s i o n , g e r b i l s a n d h a m s t e r s d i d n o t u s e f l a v o r c u e s t h a t i n d i c a t e c a l o r i c d e n s i t y a s a i d s i n l o c a t i n g a h i g h c a l o r i e f o o d s o u r c e on a r a d i a l - a r m maze. B o t h s p e c i e s were a b l e t o use f l a v o r c u e s t o d e t e c t c a l o r i c d e n s i t y . However, n e i t h e r r o d e n t s p e c i e s p r e f e r e n t i a l l y v i s i t e d h i g h - c a l o r i e arm l o c a t i o n s t h a t were m a r k e d by f l a v o r s p r e v i o u s l y a s s o c i a t e d w i t h a h i g h - and l o w - c a l o r i e f o o d i t e m . H a m s t e r s , h o w e v e r , d i d p r e f e r t o d r i n k f r o m t h e s e s i t e s . On b o t h t h e 8- and 17-arm r a d i a l maze, h a m s t e r s l o c a t e d f o o d r e w a r d s i n a h a r v e s t i n g f a s h i o n by u s i n g a c i r c l i n g s t r a t e g y . G e r b i l s d i d n o t a p p e a r t o use a f o o d - s e a r c h s t r a t e g y . The o b s e r v e d d i s p a r i t i e s b e t w e e n h a m s t e r s a n d g e r b i l s may r e f l e c t d i f f e r e n t b i o l o g i c a l c o n s t r a i n t s ( i . e ., c h e e k p o u c h e s o r l o c o m o t i o n ) , d i f f e r e n t f e e d i n g s t r a t e g i e s a t v a r i o u s p h y s i o l o g i c a l s t a t e s , d i f f e r e n t i n t e r p r e t a t i o n s o f f o o d q u a l i t y , 88 o r d i f f e r e n t f o o d g a t h e r i n g s t r a t e g i e s d e p e n d e n t upon t h e use a n d a v a i l a b i l i t y o f e n v i r o n m e n t a l c u e s . 89 R e f e r e n c e s Adam, W.R. ( 1 9 7 3 ) . N o v e l d i e t p r e f e r e n c e i n p o t a s s i u m -d e f i c i e n t r a t s , J o u r n a l o f C o m p a r a t i v e a n d P h y s i o l o g i c a l  P s y c h o l o g y , 84, 2 8 6 - 2 8 8 . A n d i k , I . , D o n h o f f e r , S., F a r k a s , M., & S c h m i d t , P. ( 1 9 6 3 ) . A m b i e n t t e m p e r a t u r e a n d s u r v i v a l on a p r o t e i n - d e f i c i e n t d i e t . B r i t i s h J o u r n a l o f N u t r i t i o n , 17, 2 5 7 - 2 6 1 . B a r n e t t , S. A., Cowan, P. E., R a d f o r d , G. G., & P r a k a s h , I . ( 1 9 7 5 ) . P e r i p h e r a l a n o s m i a and t h e d i s c r i m i n a t i o n o f p o i s o n e d f o o d by R a t t u s r a t t u s L. B e h a v i o r a l B i o l o g y , 13 , 183-190. B a t s o n , J . D., B e s t , M. R., P h i l i p p s , D. L., P a t e l , H., & G i l l e l a n d , K. R. ( 1 9 8 6 ) . F o r a g i n g on t h e r a d i a l - a r m maze: e f f e c t s o f a l t e r i n g t h e r e w a r d a t a t a r g e t l o c a t i o n . A n i m a l L e a r n i n g & B e h a v i o r , 14, 241-248. ' B o l l e s , R. C , H a y w a r d , L., & C r a n d a l l , C. ( 1 9 8 1 ) . C o n d i t i o n e d t a s t e p r e f e r e n c e s b a s e d on c a l o r i c d e n s i t y . J o u r n a l o f E x p e r i m e n t a l P s y c h o l o g y : A n i m a l B e h a v i o r  P r o c e s s e s , 7, 59-69. Bond, A. B., Cook, R. G., & Lamb, M. R. ( 1 9 8 1 ) . S p a t i a l memory a n d t h e p e r f o r m a n c e o f r a t s a nd p i g e o n s i n t h e r a d i a l - a r m maze. A n i m a l L e a r n i n g & B e h a v i o r , 9, 575-580. B o o t h , D. A. ( 1 9 7 2 ) . C o n d i t i o n e d s a t i e t y i n t h e r a t . J o u r n a l  o f C o m p a r a t i v e and P h y s i o l o g i c a l P s y c h o l o g y , 8 1 , 4 5 7 - 4 7 1 . B r o w e r , J . V. ( 1 9 5 8 ) . E x p e r i m e n t a l s t u d i e s o f m i m i c r y i n some N o r t h A m e r i c a n b u t t e r f l i e s : I . t h e m o n a r c h , Danaus  p l e x i p p u s , and v i c e r o y , L i m e n i t i s a r c h i p p u s a r c h i p p u s . 90 E v o l u t i o n , 12, 32-47. B r u c e , H. M., & K e n n e d y , G. C. ( 1 9 5 1 ) . The c e n t r a l n e r v o u s c o n t r o l o f f o o d a n d w a t e r i n t a k e . P r o c e e d i n g s o f t h e R o y a l S o c i e t y S e r i a l B. 138, 528-544. Domjan, M., & G a l e f , B. G. J r . ( 1 9 8 3 ) . B i o l o g i c a l c o n s t r a i n t s on i n s t r u m e n t a l a n d c l a s s i c a l c o n d i t i o n i n g : r e t r o s p e c t a n d p r o s p e c t . A n i m a l L e a r n i n g & B e h a v i o r , 11, 1 5 1-161. E c k e r m a n , D. A. ( 1 9 8 0 ) . M onte C a r l o e s t i m a t i o n o f c h a n c e p e r f o r m a n c e f o r t h e r a d i a l arm maze. B u l l e t i n o f t h e  P s y c h o n o m i c S o c i e t y , 15, 9 3 - 9 5 . E m l e n , J . M. ( 1 9 6 6 ) . The r o l e o f t i m e a n d e n e r g y i n f o o d p r e f e r e n c e . A m e r i c a n N a t u r a l i s t , 100, 6 1 1 - 6 1 7 . F o r e m a n , N. ( 1 9 8 5 ) . A l g o r i t h m i c r e s p o n d i n g on t h e r a d i a l - a r m maze i n r a t s d o e s n o t a l w a y s i m p l y a b s e n c e o f s p a t i a l e n c o d i n g . Q u a r t e r l y J o u r n a l o f E x p e r i m e n t a l P s y c h o l o g y , 37B, 3 3 3 - 3 5 8 . G a l e f , B. G. J r . , K e n n e t t , D. J . , & Wigmore, S. W. ( 1 9 8 4 ) . T r a n s f e r o f i n f o r m a t i o n c o n c e r n i n g d i s t a n t f o o d s i n r a t s : a r o b u s t phenomenon. A n i m a l L e a r n i n g & B e h a v i o r , 12, 2 9 2 - 2 9 6 . G a l e f , B. G. J r . , & C l a r k e , M. M. ( 1 9 7 1 ) . S o c i a l f a c t o r s i n t h e p o i s o n a v o i d a n c e a n d f e e d i n g b e h a v i o r o f w i l d a nd d o m e s t i c a t e d r a t p u p s . J o u r n a l o f C o m p a r a t i v e and P h y s i o l o g i c a l P s y c h o l o g y , 75, 3 41-357. G a l e f , B. G. J r . , & C l a r k e , M. M. ( 1 9 7 2 ) . M o t h e r ' s m i l k and a d u l t p r e s e n c e : two f a c t o r s d e t e r m i n i n g d i e t a r y s e l e c t i o n 91 by w e a n l i n g r a t s . J o u r n a l o f C o m p a r a t i v e a nd P h y s i o l o g i c a l P s y c h o l o g y , 38, 2 2 0 - 2 2 5 . G a l e f , B. G. J r . , & H e n d e r s o n , P. W. ( 1 9 7 2 ) . M o t h e r ' s m i l k : a d e t e r m i n a n t o f t h e f e e d i n g p r e f e r e n c e o f w e a n l i n g r a t p u p s . J o u r n a l o f C o m p a r a t i v e a n d P h y s i o l o g i c a l P s y c h o l o g y , 78, 2 1 3 - 2 1 9 . G a l e f , B. G. J r . , & S h e r r y , D. F. ( 1 9 7 3 ) . M o t h e r ' s m i l k : a medium f o r t r a n s m i s s i o n o f c u e s r e f l e c t i n g t h e f l a v o r o f m o t h e r ' s d i e t . J o u r n a l o f C o m p a r a t i v e a n d P h y s i o l o g i c a l P s y c h o l o g y , 8 3 , 374-378. G a r c i a , J . , H a n k i n s , W. G., & R u s i n i a k , K. W. ( 1 9 7 4 ) . B e h a i v o r a l r e g u l a t i o n o f t h e m i l i e u i n t e r n e i n man and r a t . S c i e n c e , 185, 8 2 4 - 8 3 1 . G i r a l d e a u , L. A., & K r a m e r , D. L. ( 1 9 8 2 ) . The m a r g i n a l v a l u e t h e o r e m : a q u a n t i t a t i v e t e s t u s i n g l o a d s i z e v a r i a t i o n i n a c e n t r a l p l a c e f o r a g e r , t h e e a s t e r n c h i p m u n k , T a m i a s  s t r i a t u s , A n i m a l B e h a v i o r , 30, 1036-1042. H a n d a l , P. J . ( 1 9 6 5 ) . I m m e d i a t e a c c e p t a n c e o f s o d i u m s a l t s by s o d i u m d e f i c i e n t r a t s . P s y c h o n o m i c S c i e n c e , 3_, 315-316. H a r r i s , L. J . , C l a y , J . , H a r g r e a v e s , F., & Ward, A. ( 1 9 3 3 ) . A p p e t i t e a n d c h o i c e o f d i e t : t h e a b i l i t y o f t h e v i t a m i n B d e f i c i e n t r a t t o d i s c r i m i n a t e b e t w e e n d i e t s c o n t a i n i n g a n d l a c k i n g t h e v i t a m i n . P r o c e e d i n g s o f t h e R o y a l  Soc i e t y , 113 H i n d e , R. A., & S t e v e n s o n - H i n d e , J . ( E d s . ) ( 1 9 7 3 ) . C o n s t r a i n t s on L e a r n i n g . L o n d o n : A c a d e m i c P r e s s . Hogan, J . A. ( 1 9 7 3 ) . How y o u n g c h i c k s l e a r n t o r e c o g n i z e 92 f o o d . I n R. A. H i n d e & J . S t e v e n s o n - H i n d e ( E d s . ) C o n s t r a i n t s on L e a r n i n g , ( p p . 1 1 9 - 1 3 9 ) . L o n d o n : A c a d e m i c P r e s s . H u g h e s , R. N. ( 1 9 8 1 ) . M a x i m i z i n g n e t e n e r g y r e t u r n s f r o m f o r a g i n g . I n C. R. Townsend & P. C a l o w ( E d s . ) P h y s i o l o g i c a l e c o l o g y . ( p p . 8 6 - 1 0 8 ) . O x f o r d : B l a c k w e l l S c i e n t i f i c P u b l i c a t i o n s . K o t l e r , B. P. ( 1 9 8 4 ) . R i s k o f p r e d a t i o n a n d t h e s t r u c t u r e o f d e s e r t r o d e n t c o m m u n i t i e s . E c o l o g y , 65, 6 8 9 - 7 0 1 . K r e b s , J . R., S t e p h e n s , D. W., & S u t h e r l a n d , W. J . ( 1 9 8 3 ) . P e r s p e c t i v e s i n o p t i m a l f o r a g i n g . I n A. H. B r u s h & G. A. C l a r k , J r . ( E d s . ) P e r s p e c t i v e s i n O r n i t h o l o g y . ( p p . 1 6 5 - 2 1 6 ) . C a m b r i d g e : C a m b r i d g e P r e s s . L a t , J . ( 1 9 6 7 ) . S e l f - s e l e c t i o n o f d i e t a r y c o m p o n e n t s . I n C. F. Code & W. H e i d e l ( E d s . ) Handbook o f P h y s i o l o g y , S e c t . 6 A l i m e n t a r y C a n a l . V o l . 1 , ( p p . 3 6 7 - 8 8 6 ) . A m e r i c a n P h y s i o l o g i c a l S o c i e t y , W a s h i n g t o n , D.C. L e g e r , D. W., O w i n g s , D. H., & C o s s , R. C. ( 1 9 8 3 ) . B e h a v i o r a l e c o l o g y o f t i m e a l l o c a t i o n i n C a l i f o r n i a g r o u n d s q u i r r e l s ( S p e r m o p h i l u s b e e c h e y i : m i c r o h a b i t a t e f f e c t s . J o u r n a l o f C o m p a r a t i v e P s y c h o l o g y , 97, 2 8 3 - 2 9 1 . LeMagnen, J . , & T a l l o n , S. ( 1 9 6 6 ) . L a p e r i o d i c i t e s p o n t a n e e de l a p r i s e d ' a l i m e n t s a d l i b i t u m du R a t b l a n c . J o u r n a l de P h y s i o l o g i e ( P a r i s ) , 58, 3 2 3 - 3 4 9 . L i m a , S. L., & V a l o n e , I . J . ( 1 9 8 6 ) . I n f l u e n c e o f p r e d a t i o n r i s k on d i e t s e l e c t i o n : a s i m p l e e x a m p l e i n t h e g r e y s q u i r r e l . A n i m a l B e h a v i o r , 34, 536-544. 93 L o b e l , P. S., & Ogden, J . C. ( 1 9 8 1 ) . F o r a g i n g by t h e h e r b i v o r o u s p a r r o t f i s h S p a r i s o m a r a d i a n s . M a r i n e B i o l o g y , 64, 173-183. M e h i e l , R., & B o l l e s , R. C. ( 1 9 8 4 ) . L e a r n e d f l a v o r p r e f e r e n c e s b a s e d on c a l o r i c o u t c o m e . A n i m a l L e a r n i n g a n d B e h a v i o r , 12, 42 1 - 4 2 7 . M e l c e r , T., & T i m b e r l a k e , W. ( 1 9 8 5 ) . P o i s o n a v o i d a n c e a n d p a t c h ( l o c a t i o n ) s e l e c t i o n i n r a t s . A n i m a l L e a r n i n g a n d B e h a v i o r , 13, 60-68. M i l t o n , K. ( 1 9 7 9 ) . F a c t o r s i n f l u e n c i n g l e a f c h o i c e by h o w l e r m onkeys: a t e s t o f some h y p o t h s i s o f f o o d s e l e c t i o n by g e n e r a l i s t h e r b i v o r e s . A m e r i c a n N a t u r a l i s t , 114, 362-378. M i z u m o r i , S. J . Y., R o s e n z w e i g , M. R., & K e r m i s c h , M. G. (.1982). F a i l u r e o f m i c e t o d e m o n s t r a t e s p a t i a l memory i n t h e r a d i a l maze. B e h a v i o r a l a n d N e u r a l B i o l o g y , 35, 3 3 -45. M o o r e , F. R., & O s a d c h u k , T. E. ( 1 9 8 2 ) . S p a t i a l memory i n a p a s s e r i n e m i g r a n t . I n F. P a p i & H. G. W a l l r a f f ( E d s . ) A v i a n N a v i g a t i o n . ( p p . 3 1 9 - 3 2 5 ) . New Y o r k : S p r i n g e r . O l t o n , D. S. ( 1 9 7 8 ) . C h a r a c t e r i s t i c s o f s p a t i a l memory. I n S. H. H u l s e , H. F o w l e r , & W. K. H o n i g ( E d s . ) C o g n i t i v e P r o c e s s e s i n A n i m a l B e h a v i o r , ( p p . 3 4 1 - 3 7 3 ) . H i l l s d a l e New J e r s e y : E r l b a u m . O l t o n , D. S., & C o l l i s o n , C. ( 1 9 7 9 ) . I n t r a m a z e c u e s a n d " o d o r t r a i l s " f a i l t o d i r e c t c h o i c e b e h a v i o r on an e l e v a t e d maze. A n i m a l L e a r n i n g & B e h a v i o r , 1_, 221-223. 94 O l t o n , D. S., C o l l i s o n , C , & W e r z , M. A. ( 1 9 7 7 ) . S p a t i a l memory a n d r a d i a l - a r m maze p e r f o r m a n c e o f r a t s . L e a r n i n g  and M o t i v a t i o n , 8, 289-314. O l t o n , D. S., & S a m u e l s o n , R. J . ( 1 9 7 6 ) . Remembrance o f p l a c e s p a s s e d , s p a t i a l memory i n r a t s . J o u r n a l o f  E x p e r i m e n t a l P s y c h o l o g y ; A n i m a l B e h a v i o r P r o c e s s e s , 2, 97-116. O l t o n , D. S., & Werz, M. A. ( 1 9 7 8 ) . H i p p o c a m p a l f u n c t i o n a n d b e h v i o u r : s p a t i a l d i s c r i m i n a t i o n a n d r e s p o n s e i n h i b i t i o n . P h y s i o l o g y a n d B e h a v i o u r , 2 0, 59 7 - 6 0 5 . P o u c e t , B., C h a p u i s , N., D u r u p , M., & T h i n u s - B l a n c , C. ( 1 9 8 6 ) . A s t u d y o f e x p l o r a t o r y b e h a v i o r a s an i n d e x o f s p a t i a l k n o w l e d g e i n h a m s t e r s . A n i m a l L e a r n i n g a n d B e h a v i o r , 14, 9 3 - 1 0 0 . P u l l i a m , H. R. ( 1 9 8 0 ) . Do c h i p p i n g s p a r r o w s f o r a g e o p t i m a l l y ? A r d e a , 6 8 , 7 5 - 8 2 . P y k e , G. H., P u l l i a m , H. R., & C h a r n o v , E. L. ( 1 9 7 7 ) . O p t i m a l f o r a g i n g : a s e l e c t i v e r e v i e w o f t h e o r y a n d t e s t s . Q u a r t e r l y R e v i e w o f B i o l o g y , 52, 137-154. R a p p o r t , D. J . ( 1 9 8 0 ) . O p t i m a l f o r a g i n g f o r c o m p l e m e n t a r y r e s o u r c e s . A m e r i c a n N a t u r a l i s t , 116, 324-346. R e i c h m a n , 0. J . , & O b e r s t e i n , D. ( 1 9 7 7 ) . S e l e c t i o n o f s e e d d i s t r i b u t i o n t y p e s by Dipodymus m e r r i a m i a n d P e r o g n a t h u s a m p l u s . E c o l o g y , 58, 6 3 6 - 6 4 3 . R e v u s k y , S. H. ( 1 9 6 7 ) . Hunger l e v e l d u r i n g f o o d c o n s u m p t i o n : e f f e c t s on s u b s e q u e n t p r e f e r e n c e . P s y c h o n o m i c S c i e n c e , 7 , 109-110. 95 R i c h t e r , C. P. ( 1 9 4 2 - 1 9 4 3 ) . T o t a l s e l f - r e g u l a t o r y f u n c t i o n s i n a n i m a l s a n d human b e i n g s . H a r v e y L e c t u r e S e r i e s , 38, 6 3 - 1 0 3 . R i c h t e r , C. P. ( 1 9 5 5 ) . S e l f - r e g u l a t o r y f u n c t i o n s d u r i n g g e s t a t i o n a n d l a c t a t i o n . 2nd T r a n s a t l a n t i c C o n f e r e n c e on  G e s t a t i o n , ( p p . 1 1 - 9 3 ) . P r i n c e t o n , N. J . R i l e y , A. L., C l a r k e , C. M. ( 1 9 7 7 ) . C o n d i t i o n e d t a s t e a v e r s i o n s : a b i b l i o g r a p h y . I n L. M. B a r k e r , M. R. B e s t , & M. Domjan ( E d s . ) L e a r n i n g M e c h a n i s m s i n F o o d  S e l e c t i o n . ( p p . 5 9 3 - 6 1 0 ) . Waco T e x a s : B a y l o r U n i v e r s i t y P r e s s . R o b e r t s , W. A. ( 1 9 8 4 ) . Some i s s u e s i n a n i m a l s p a t i a l memory. I n H. L. R o i t b l a t , T. G. B e v e r , & H. S. T e r r a c e ( E d s . ) A n i m a l C o g n i t i o n , ( p p . 4 2 5 - 4 4 3 ) . H i l l s d a l e New J e r s e y : E r l b a u m . R o b e r t s , W. A., & Van V e l d h u i z e n , N. ( 1 9 8 5 ) . S p a t i a l memory. I n H. L. R o i t b l a t , T. G. B e v e r , & H. S. T e r r a c e ( E d s . ) A n i m a l C o g n i t i o n . ( p p . 4 2 5 - 4 4 3 ) . H i l l s d a l e New J e r s e y : E r l b a u m . R o i t b l a t , H. L., Tham, W., & G o l u b , L. ( 1 9 8 2 ) . P e r f o r m a n c e o f B e t t a s p l e n d e n s i n a r a d i a l arm maze. A n i m a l L e a r n i n g &  B e h a v i o r , 10, 108-114. R o s e n z w e i g , M. L., S m i g e l , B. W., & K r a f t , A. ( 1 9 7 5 ) . P a t t e r n s o f f o o d , s p a c e , and d i v e r s i t y . I n I . P r a k a s h , & P. K. Ghosh ( E d s . ) R o d e n t s i n D e s e r t E n v i r o n m e n t s , ( p p . 2 4 1 - 2 6 8 ) . Hague: N e t h e r l a n d s : W. J u n k . R o z i n , P. ( 1 9 6 7 ) . T h i a m i n e s p e c i f i c h u n g e r . I n C. F. Code & 96 W. H e i d e l ( E d s . ) Handbook o f P h y s i o l o g y , S e c t . 6 A l i m e n t a r y C a n a l . V o l . 1, F o o d a n d W a t e r I n t a k e . ( p p . 4 1 1 - 4 3 1 ) . B a l t i m o r e : W i l l i a m s & W i l k i n s . R o z i n , P. ( 1 9 6 8 ) . A r e c a r b o h y d r a t e a n d p r o t e i n i n t a k e s s e p a r a t e l y r e g u l a t e d ? J o u r n a l o f C o m p a r a t i v e P h y s i o l o g y a n d P s y c h o l o g y , 65, 23-29. R o z i n , P. ( 1 9 7 7 ) . The s e l e c t i o n o f f o o d s by r a t s , humans, a n d o t h e r a n i m a l s . I n J . R o s e n b l a t t , R. A. H i n d e , C. B e e r , & E. Shaw ( E d s . ) L e a r n i n g M e c h a n i s m s i n F o o d S e l e c t i o n . ( p p . 2 1 - 7 6 ) . Waco: T e x a s : B a y l o r U n i v e r s i t y P r e s s . S c h o e n e r , T. W. ( 1 9 7 1 ) . T h e o r y o f f e e d i n g s t r a t e g i e s . A n n u a l  R e v i e w o f E c o l o g y a n d S y s t e m a t i c s . 2, 369-404. S h e t t l e w o r t h , S. J . ( 1 9 8 2 ) . F u n c t i o n a n d m e c h a n i s m i n l e a r n i n g . I n M. Z e i l e r & P. H. Harzem ( E d s . ) A d v a n c e s  i n A n a l y s i s o f B e h a v i o r ( V o l . 3 ) . New Y o r k : W i l e y . S p e t c h , M. L., & E d w a r d s , C. A. ( 1 9 8 6 ) . S p a t i a l memory i n p i g e o n s ( Columba l i v i a ) i n an o p e n - f i e l d f e e d i n g e n v i r o n m e n t . J o u r n a l o f C o m p a r a t i v e P s y c h o l o g y . 100, 2 6 6 - 2 7 8 . T i n b e r g e n , J . ( 1 9 8 1 ) . F o r a g i n g d e c i s i o n s i n s t a r l i n g s ( S t u r n u s  v u l g a r i s L . ) . A r d e a , 69, 1-67. V a d a s , R. L. ( 1 9 7 7 ) . P r e f e r e n t i a l f e e d i n g : an o p t i m i z a t i o n s t r a t e g y i n s e a u r c h i n s . E c o l o g y M o n o g r a p h , 47, 3 3 7 - 3 7 1 . W i l k i e , D. M., & S l o b i n , P. ( 1 9 8 3 ) . G e r b i l s i n s p a c e : p e r f o r m a n c e on t h e 17-arm r a d i a l maze. J o u r n a l o f t h e 97 E x p e r i m e n t a l A n a l y s i s o f B e h a v i o r , 40, 3 0 1 - 3 1 2 . W i l k i e , D. M. , S p e t c h , M. L., & Chew, L. ( 1 9 8 1 ) . The r i n g c l o v e ' s s h o r t - t e r m memory c a p a c i t y f o r s p a t i a l i n f o r m a t i o n . A n i m a l B e h a v i o r , 29, 6 3 9 - 6 4 1 . Wong, R. ( 1 9 8 6 ) . C a l o r i c b a l a n c i n g a n d s u c r o s e i n t a k e o f h a m s t e r s a n d g e r b i l s . A m e r i c a n J o u r n a l o f P s y c h o l o g y , 99 , 355-366. Y o e r g , S. J . , & K a m i l , A. C. ( 1 9 8 2 ) . R e s p o n s e s t r a t e g i e s i n t h e r a d i a l arm maze: r u n n i n g a r o u n d i n c i r c l e s . A n i m a l  L e a r n i n g & B e h a v i o r , 10, 53 0 - 5 3 4 . Z a h o r i k , D. M., & M a i e r , S. F. ( 1 9 6 9 ) . A p p e t i t i v e c o n d i t i o n i n g w i t h r e c o v e r y f r o m t h i a m i n e d e f i c i e n c y a s t h e u n c o n d i t i o n e d s t i m u l u s . P s y c h o n o m i c S c i e n c e , 17, 309-310. Z o l d e c k , L., & R o b e r t s , W. A. ( 1 9 7 8 ) . The s e n s o r y b a s i s o f s p a t i a l memory i n t h e r a t . A n i m a l L e a r n i n g & B e h a v i o r , 6 , 7 7 - 8 1 . 

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