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Behav Ecol Sociobiol (1985) 16:249 -255 Behavioral Ecologyand Sociobiology9 Springer-Ve rlag 1985

On the funct ion o f warning co lorat ion:a b lack and ye l low pattern inhibi ts prey-at tackby na ive do m es t ic ch i cksW e r n e r S c h u le r a n d E l k e H e s seI I . Zoologisches Ins t i tu t der Univers it /i t, Ber liner St rasse 28, D-3400 G6t t ingen, F edera l R epubl ic of G erm anyReceived April 10, 1984 / Accepted August 31, 1984

Summary. Y o u n g c h i c k s w e r e o f f e r e d a c h o i c e o fw a r n i n g ly c o l o u r e d b l a c k a n d y e l lo w a n d n o n -w a r n i n g l y c o l o u r e d g r e e n ( o r o l i v e ) p r e y . U n f e dc h i c k s w e r e g i v e n p a l a t a b l e p a i n t e d m e a l w o r m s o nt h e i r f i r s t d a y . T h e y d i r e c t e d t h e i r f i r s t p e c k a tb o t h c o l o u r t y p e s a t t h e s a m e p r o b a b i l i t y ; h o w -e v e r , t h e y a t e t h e w a r n i n g l y c o l o u r e d o n e s a t am u c h l o w e r r a t e . T h i s i s d u e t o a n i n h i b i t i o n o fa t t a c k w h i c h b e c o m e s e f f e c t i v e a f t e r p e c k i n g .C h i c k s w h i c h w e r e a f e w d a y s o l d s h o w e d t h e s a m eb e h a v i o u r . S i n c e th e c o n t r o l p r e y w a s i n t h i s c a s ep a i n t e d w i t h a n o l i v e m i x t u r e c o n t a i n i n g t h e s a m ec o l o u r s a s t h e w a r n i n g l y c o l o u r e d m e a l w o r m s , i tc a n b e c o n c l u d e d t h a t t h e i n h i b i t i o n i s c a u s e d b yt h e b l a c k a n d y e l l o w c o l o r a t io n . W i t h a c c u m u l a t -i n g p o s i t iv e e x p e r i e n c e o f t h e c h i c k s , t h e i n h i b i t i o nd e c re a s ed . F o r p e r m a n e n t a v o i d a n c e it m u s t t h er e -f o r e b e s u p p l e m e n t e d b y u n p l e a s a n t e x p e ri e n c e.A c c o r d i n g l y , c h ic k s h a n d l e d t h e u n p a l a t a b l e b l a c ka n d y e l l o w r i n g e d c a t e r p i l l a r s o f Tyria jacobaeaeo n l y a f e w t i m e s a n d a l w a y s f o r a s h o r t p e r i o dw h e n o f f e r e d r e p e a te d l y . T h e i n h i b i t i o n c a u s e d b yt h e b l a c k a n d y e l l o w p a t t e r n i s a t t r i b u t e d t o a g e -n e t i c a l l y f i x e d p r e d i s p o s i t i o n t o a v o i d w a r n i n g l yc o l o u r e d b l a c k a n d y e l lo w p r e y w h i c h is t h e r e s u lto f e v o l u t i o n a r y a d a p t a t i o n .

IntroductionI t i s gene ra l l y he l d t ha t warn i ng co l o ra t i ons , i . e .t h e c o n s p i c u o u s p a t t e r n s o f n o x i o u s p r e y a n i m a l s ,a r e s i g n a l s i n d i c a t i n g u n p a l a t a b i l i t y t o p o t e n t i a lp r e d a t o r s . I n m o s t c a s e s o f w a r n i n g l y c o l o u r e d i n-s e c ts s t u d i e d , th e a v o i d a n c e r e s p o n s e o f t h e p r e d a -t o r is a c q u i r e d ( M o r g a n 1 8 9 6; M o s t l e r 1 9 3 5; W i n -decker 1939 ; S chne i de r 1954 ; J .V .Z . B rower 1958 ;L . P . B r o w e r 1 9 6 9 ; E v a n s a n d W a l d b a u e r 1 9 8 2 ;

b u t s e e D a v i e s a n d G r e e n 1 97 6) . F o r a l o n g t i m ei t w a s t h e r e f o r e a s s u m e d t h a t t h e o n l y f u n c t i o no f w a r n i n g c o l o r a t i o n i s t o f a c i l it a te a v o i d a n c el e a rn i n g a n d r e c o g n it io n . W a r n i n g c o l o r a t io n w a sr e g a r d e d t o b e o n l y a " b e s o n d e r s p r ~ i g na n te s D r e s -s u rm erk m a l " , i . e . an e s pec i a l ly s i gn i f ican t s t i m u l u sfo r l ea rn i ng (W i ck l e r 1968 , p . 118 ) . Ev i dence fo ri n n a t e a v o i d a n c e r e s p o n s e s t o w a r n i n g l y c o l o u r e ds n a k e s w a s r e p o r t e d a t f i r s t f o r p r e d a t o r y f i s h e s( R u b i n o f f a n d K r o p a c h 1 97 0) a n d a m a m m a l(Ge h l bac h 1972 ). La t e r , S m i t h (1975 , 1977) dem -o n s t r a t e d i n n a t e a v o i d a n c e r e s p o n s e s t o c o r a ls n a k e p a t t e r n s i n t w o n e o t r o p i c a l b i r d s p e ci e s ( se ea l s o C a l d w e l l a n d R u b i n o f f 1 98 3) . T h e r e f o r e i t w a sc o n c l u d e d t h a t " s o m e p r e d a t o r s h a v e e v o l v e d i n-n a t e a v o i d a n c e r e a c t i o n s t o p a r t i c u l a r a p o s e m a t i cs i gn a l s . . . , b u t m o r e o f t e n p r e d a t o r s l e a r n t o a v o i ds u c h p r e y . . . " ( H a r v e y a n d G r e e n w o o d 1 9 78 ).T h e s t a t e m e n t t h a t t h e a v o i d a n c e r e a c t i o n i sa c q u i r e d d o e s n o t s a y h o w n a i v e b i r d s r e s p o n dt o w a r n i n g l y c o l o u r e d p r e y , e v e n t h o u g h i t s u g -g e s t s t h a t t h e y r e a c t t o i t i n t h e s a m e m a n n e r a st o o t h e r n o v e l p r e y . I n c o n t r a s t t o t h i s, e x p e r i m e n t sc a r r i e d o u t r e c e n t ly h a v e s h o w n t h a t i n e x p e r i e n c e db i rd s k i l l , even du r i ng t he f i r s t encoun t e r , warn -i n g l y c o l o u r e d n o x i o u s i n s e ct s l es s f r e q u e n t l y t h a no t he r p rey (W i k l und and J f i rv i 1982 ) . Th i s was a t -

t r i b u t e d t o t h e c h e m i c a l a n d m e c h a n i c a l d e f e n s eo f t h e s p e c ie s te s t ed . H o w e v e r , w a r n i n g c o l o r a t i o nw i t h o u t n o x i o u s p r o p e r t i e s m a y h a v e a s i m i l a r e f -f e c t : N a i v e b i r d s e a t w a r n i n g l y c o l o u r e d h a r m l e s sp rey i t em s a t f i r s t l e s s f r equen t l y t han d i f f e ren t l yc o l o u r e d o n e s ( C o p p i n g e r 1 9 7 0 ; S c h u l e r 1 9 8 2 ) .C o p p i n g e r a t t r i b u t e s t h i s t o t h e u n u s u a l a p p e a r -a n c e o f w a r n i n g l y c o l o u r e d p r e y ( n o v e l t y h y p o t h e -s i s ) , w h e r e a s S c h u l e r a s s u m e s a n i n n a t e t e n d e n c yt o a v o i d s u c h p r e y . T h e e s s e n t i a l p o i n t i s t h a tC o p p i n g e r d r a w s u p o n a c o m m o n u ns p e c ia l iz e db e h a v i o u r w h e r e a s S c h u l e r a s s u m e s a s p e c i fi c a d -

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25 0a p t a t i o n o n t h e p r e d a t o r ' s s id e . A d e c i s i o n a s t ow h i c h o f th e s e t w o e x p l a n a t i o n s i s c o r r e c t i s i m p o s -s i bl e o n t h e b a s i s o f a v a i l a b le d a t a ( se e C u r i o 1 9 7 6 ,p . 1 0 5 f o r C o p p i n g e r ' s r e s u lt s ) .

I n t h is i n v e s t i g a t i o n w e h a v e t r i e d to d i s p r o v eC o p p i n g e r ' s n o v e l t y h y p o t h e s i s . F o r t h e e x p e ri -m e n t s a p r e c o c i o u s b i r d s p e c i es w h i c h s t a r ts e a t i n go n i ts o w n s h o r t l y a f t er h a t c h i n g s e e m e d t o b em u c h m o r e a p p r o p r i a t e t h a n t h e a lt r i c ia l s pe c ie st e s t e d u n t i l n o w , b e c a u s e t h e e x p e r i e n c e g a i n e d b yt h e e x p e r i m e n t a l s u b j e c t s p r i o r t o t e s t i n g c a n b ec o n t r o l l e d i n a p r e c o c i o u s s p e c ie s m u c h m o r e e a s i -l y. W e c h o s e a s o u r e x p e r i m e n t a l s p e c ie s t h e d o -m e s t i c c h i c k e n , w h i c h e a t s, a s d o e s i ts a n c e s t o r ,t he R e d J u n g l e F o w l (Ga l l u s g a l l u s ) ( C o l l i a s a n dC o l l i a s 1 9 6 7 ), in s e c t s a n d o t h e r i n v e r t e b r a t e s i na d d i t i o n t o s e e d s a n d p l a n t m a t e r i a l ( e . g . M c B r i d ee t a l. 1 9 6 9 ; F 6 1 s c h a n d S t a h e l 1 9 8 2 ) . U n d e r c o n d i -t i o n s o f f e r a l li fe , i n v e r t e b r a t e p r e y s e e m s t o b ee s p e ci a l l y i m p o r t a n t f o r y o u n g c h i c k s ( f o r o t h e rP h a s i a n i d a e s ee e .g . G l u t z y o n B l o t z h e i m e t a l.1 9 7 3) s i nc e t h e y h a v e h i g h e r p r o t e i n r e q u i r e m e n t st h a n a d u l t s ( S c o t t e t a l . 1 9 7 8 ) .

T h e d o m e s t i c c h i c k e n i s a l s o s u i ta b l e f o r t h ep r e s e n t i n v e s t ig a t i o n b e c a u s e o n e d o e s n o t h a v et o a s s u m e t h a t a n a d a p t a t i o n t o w a r n i n g l y c o l -o u r e d p r e y , p o s s i b l y e x i s t i n g in i ts w i l d a n c e s t o r ,h a s b e e n l o s t i n t h e c o u r s e o f d o m e s t i c a t i o n , s in c ec h i c k s w e r e e x p o s e d - a s l o n g a s t h e y w e r e k e p to u t d o o r s - a t l ea s t t o t h e s e l e c ti o n p r e s s u r e e x e r t e db y w a r n i n g l y c o l o u r e d b l a c k a n d y e l lo w w a s p s( V e s p i d a e ) . T h i s is i n d i c a t e d b y th e o b s e r v a t i o nt h a t a d u l t c h i c k s r e j e c t w a s p s a s w e ll a s b l a c k a n dy e l l o w b a n d e d c a t e rp i l l a rs o n s i g ht ( W i n d e c k e r1 9 3 9 , p . 1 3 1 f ; B e r g m a n n 1 9 5 3 , p . 1 8 4 ) .

B a s e d o n t h e s e c o n s i d e r a t i o n s w e d e c i d e d t ou s e a b l a c k a n d y e l l o w r i n g p a t t e r n , s i m i l a r t o t h a tt e s t ed i n y o u n g s t a r l in g s ( S c h u l e r 1 9 8 2 ), a s th ew a r n i n g c o l o r a t i o n i n o u r t es ts .

Ma t er i a l s a nd m et ho dsThe exper imenta l b i rds were unsexed broiler chicks (Lo hm annhybr ids) which were obta ine d for each experimenta l series ont he mor n i ng o f t he ha t c h i ng da y f r om a l oc a l ha tc he r y .The ar t i f ica l prey used was pa in ted mealworms ( larvae ofTenebrio m olitor L). In one experimental series larvae of thec i nna ba r mo t h (Tyriajacobaeae, Arct i idae) were of fered addi -t ionally. The mealworms were kil led in boiling water andpainted w i th non- toxic f inger colours (ye l low: CK 22, C. Kreul ,Forc hheim ; b lack, and green: Mara bu, A r t . Nr . 030142) . Theblack and yel low larvae had fo ur equidis tant b lack r ings abo ut2 m m w ide on a ye l low backgroun d. A l l insects were s toredin a deep f reezer and thawed some minutes before the tes tsof the day s tar ted .The uncov ered tes t cage (91 x 63 x 20 cm) was m ade f romgrey PVC, except for i ts Plexiglas front. A parti t ion left anarena 65 x 62 cm whose f loor w as l ined wi th wh i t ish p aper .

In every tes t f ive la rvae of both types were of fered . They w ereplaced a l te rnate ly in two rows o f five on the f loor o f the arenaat d is tances of 4 .5 cm. Th e pos i t ion o f the types was exchan gedfor each new session. The chicks were tested in pairs since iso-lated ones are inclined to utter distress calls. Prior to the firsttest , a rb i t rar i ly taken pai rs were ma rked individual ly wi th fe l t-t ip pens . Subsequent ly , the mo re ac t ive chick of each pai r wasdes igned to b e the focus b ird for the observat ion o f behav iourduring the tests.For the tes ts the chicks examined on the f i r s t day of the i rl ives were placed in the arena. The older chicks were put intoa s tar t ing box f rom which they could be re leased by meansof a nylon thread. Th e behaviou r of the chicks was observedt h r ough a o ne - wa y mi r r o r w i ndow a nd doc um e n t e d on t a peor by an event recorder (Peiseler-Stoppdrucker). In som e testsa v i de o c a me r a a nd r e c o r de r ( Sa nyo VC 500 a nd VTC 7100 )were a lso used. The tes t was s top ped af ter 5 min o r wh en a l linsec ts ha d bee n ea ten . A f ter each tes t the nu mb er o f la rvaeeaten by both chicks together was noted .Except during testing, the chicks examined on their f irstda y we r e ke p t i n a c a r dboa r d box a nd wa r me d by me a ns o fa 150 W inf ra- red bulb (C rom pton R 125 ref lec tor ruby) . Thesechicks d id not rece ive food and water unt i l they had gonethrough the i r th i rd and las t sess ion. The chicks which weref i r s t tes ted on the i r th i rd day were accus tomed in pa i rs to thetes t cage and the s tar t ing box on the i r second day. They werehoused as a g roup in a cage s imilar to the tes t cage , the bot to mof which was l ined w i th whi ti sh paper and s t rewn wi th whi tesand. A 100 W in fra-red bu lb prod ucin g no visible l ight (ElsteinInf rarots t rahler ) provided warmth. Chicken s tar ter pe l le t s andwater were offered in white one l i tre feeders with a red base.On the f i r s t days pe l le t s were spread on the f loor and a t thesame t ime given in an ear thenware d ish . In one exper imenta lseries egg food (a mixture o f hard boi led , m ashed egg andshredd ed whea t) was given initially. O n each experimental dayfood an d water was wi thdraw n f rom al l chicks s imul taneously ;i t was replaced only after f inishing the day's tests. To avoidaccustoming the chicks to green objects (trees outside the win-dow, doo r s pa i n t e d g r ee n ), t he w i ndow a nd t he doo r s o f t heroom were covered wi th whi te paper .Th e data were treated statist ically follow ing Siegel (1956),Roh l f a nd Soka l ( 1969 ) a nd Mc C or na c k ( 1965 ). A l l P - va l uesgiven are one-ta iled, according to o ur hypothes is tha t w arninglycoloured pre y i s ea ten less requently t ha n o t he r p r e y.Resul t sT h e a t t a c k u p o n a b l a c k a n d y e l l o w p r e y i s in h i b it e dC h i c k s w h i c h h a d n e v e r b e e n f e d b e fo r e w e r e o f -f e r ed a c h o i c e b e t w e e n b l a c k a n d y e l l o w la r v a ea n d g r e e n l a r v a e t h r e e t i m e s o n t h e i r f i rs t d a y .T h i s e x p e r i m e n t w a s c a r r i e d o u t t w o t i m e s w i t ht e n p a i rs o f c hi c k s e a c h. T h e t w o g r o u p s d i f fe r e di n a c ti v i t y , as c a n o f t e n b e o b s e r v e d i n c h i c k s o ft h e s a m e b r e e d f r o m d i f fe r e n t h a t c h i n g d a y s ( c f.W a l l m a n 1 9 79 ) . H o w e v e r , b o t h t r e a t e d th e l a r v a ei n b a s i c a l l y th e s a m e m a n n e r . C a l c u l a t i n g t h e d a t af o r e a c h g r o u p s e p a r a t e ly y i e l d ed c o r r e s p o n d i n gr e su l ts a n d t h e i r d a t a w e r e t h e r e f o r e c o m b i n e d .T h r e e c h i ck s w e r e e x c l u d e d s in c e t h e y i g n o r e d t h el a r v a e i n a l l t h r e e s e s s i o n s .

I n t h e c o u r s e o f t h e t h r e e s e s s io n s t h e c h i c k s

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Fig. I a, b. Analysis of the behaviour ofthe chicks towards black and yellow orgreen prey tested on their first day.a Number of larvae approached in threesessions (mean_+ SE per focus bi rd) ;b course of events during all attacks.Handled: picked up, carried and/or bea-ten on the ground. Arrows: probabilityfor the transition to the following phase.** P

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F i g . 2 a , h . B e h a v i o u r o f t h e c h i c k s t e s t e do n t h e i r f i r s t d a y d u r i n g t h e i r f i r s t a t t a c ku p o n b l a c k a n d y e l l o w la r v a e a n d g r e e nl a r v a e . U p p er h a l f : c h i c k s a t t a c k i n gb l a c k a n d y e l l o w l a r v a e f i r s t ; lower hal f ."c h i c k s a t t a c k i n g g r e e n l a r v a e f i r s t .a T h e f i r s t a t t a c k o f e a c h c h i c k ;b t h e f i rs t a t t a c k o n t h e o t h e r c o l o u rt y p e b y t h e s a m e c h i c k s .A r r o w s : p r o b a b i l i t y f o r t h e t r a n s i t i o n t ot h e fo l l o w i n g p h a s e . * * P < 0 . 0 1 ; F i s h e re x a c t p r o b a b i l i t y t e s t f o r t h e d i f f e r e n c et o t h e c o r r e s p o n d i n g v a l u e w i th g r e e nl a r v a e

tions of weight as the black and yellow paintedlarvae, appears dark olive-coloured. The chickswere tested in this case once a day with a choiceof black and yellow larvae and olive ones fromtheir third to their tenth day of life. Apart fromthe tests they were given only egg food at first.After completing the third experimental session(on their fifth day), egg food was replaced bychicken starte r pellets.During the first three sessions these chicks be-haved in a way very similar to those tested before:When pecking at their first larva they did notchoose black and yellow significantly less fre-quently than the olive control larvae (4 vs 6 focusbirds; NS; binomial test); however, the first larvaeaten was never black and yellow (n = 7; P < 0.01 ;binomial test). The behaviour of the individualchicks showed that those birds which first attackedan olive larva, either continued handling this col-our type exclusively until eating the first larva oruntil the end o f the third session, or on ly occasion-ally and briefly pecked at black and yellow ones,whereas those chicks which had started with theblack and yellow either changed to the olive larvaeafter the first attack, or they did repeat the attackupon the former, but stopped each time after ashort period. Therefore, in this experimental seriesthe first attacks on black and yellow larvae werealso inhibited, from which it is evident that theinhibition resulted from the distribution of the col-ours but not from their taste.The behaviour of the chicks in the furthercourse of the series gives additional evidence thatthe black and yellow larvae did not taste worsethan the controls. Nine pairs of chicks were testedhere and one pair was excluded from the computa-tion because they did not eat larvae at all untilthe end of the series. In the remaining eight pairs

the mean percentage of larvae eaten continued toincrease in both colour types. In the last sessionthey did not consume significantly less black andyellow than olive larvae (mean + SE: 3.5 ___0.81 an d5.00+0, respectively; NS; Wilcoxon matched-pairs signed-ranks test). Their selectivity was there-fore essentially lower than during the first sessionin which they started eating larvae (black and yel-low: 0.25_0.25; olive: 4.00_+0.50; P 0.10; comparison of the ranks of both colourtypes by means of the Mann-Whitney U-test).Therefore this sensitive measurement indicates alsoa reduced selectivity on the part of the chicks atthe end of the experiment.The decreasing selectivity in reverse order tothe growing experience of the chicks demonstratesagain that t he black and yellow painted larvae can-not be considered as unpalatable for the chickssince unpalatability can be defined operationallybest as increasing selectivity depending on accumu-lating experience (Edmunds 1974).Stabilisation o f the inhibition by an insect 's defenseMorgan (1896) and Windecker (1939) reportedthat naive domestic chicks pecked at the black andyellow ringed larva of the cinnabar moth (Tyriajacobaeae) at first and subsequently rejected it.Both authors attributed this behaviour to the un-pleasant taste o f the caterpillar which contains his-tamine and poisonous alkaloids (Aplin et al. 1968).After having found that a black and yellow prey

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253w i t h o u t a n u n p l e a s a n t t a s t e c a n c a u s e s i m i l a rb e h a v i o u r , w e t e s t e d w h e t h e r n a i v e c h i c k s t r e a t e dt h i s c a t er p i l l a r u n d e r t h e c o n d i t i o n s o f o u r e x p e r i -m e n t s i n a n y o t h e r w a y t h a n t h e b l a c k a n d y e l lo wp a i n t e d m e a l w o r m s t e s t e d s o f a r . F o r t h i s e x p e r i -m e n t s e v e n p a i rs o f c h i c k s w e r e d a i l y g i v e n a c h o i c eo f Tyria c a te r p il l ar s a n d g r e e n m e a l w o r m s o f e q u a ll e n g t h f r o m t h e t h i r d t o t h e t e n t h d a y o f t h e i r li ve s .T h e f i rs t p e c k w a s n o t a i m e d s i g n i f i c a n t l y l es so f t e n a t t h e c a t e r p i l l a rs t h a n a t t h e g r e e n m e a l -w o r m s ( i n t w o a n d f i v e f o c u s b i r d s , r e s p e c t i v e l y ;P > 0 . 2 0 ; b i n o m i a l t es t) . I n c o n t r as t , n o n e o f t h ef i v e f o c u s b i r d s w h i c h a t e t e s t in s e c ts t o o k a c a t e r -p i l l a r f i r s t ( P < 0 . 0 5 ; b i n o m i a l t e s t ) . N o e s s e n t i a ld i f f e r e n c e c o u l d t h e r e f o r e b e s e e n b e t w e e n t h eb e h a v i o u r o f t h e se c h i ck s a n d t h o s e t e s t ed w i t hb l a c k a n d y e l l o w p a i n t e d m e a l w o r m s .I n t h e f u r t h e r c o u r s e o f t h e e x p e r i m e n t n o n eo f t h e s e v e n p a i rs c o n s u m e d a s i n g le c a t e rp i l l a r,w h e r e a s i n t h e c o r r e s p o n d i n g s e r i e s d e s c r i b e da b o v e b l a c k a n d y e l l o w p a i n t e d m e a l w o r m s w e r ee a t e n b y s ix o u t o f n i n e p a i rs . T h i s d i f f e r e n c e i ss i g n i f ic a n t ( P < 0 . 02 ; F i s h e r e x a c t p r o b a b i l i t y t e s t ).I n t h e c o u r s e o f t h e e i g h t s e s s io n s , t h e c a t e r p i ll a r sw e r e a t t a c k e d b y a l l s e v e n p a i r s , a l t h o u g h o n l ya f e w t ime s ( 3 .0 +_ 0 . 8 t ime s p e r c h i c k ) a n d a lw a y sf o r a v e r y s h o r t p e r i o d ( t o t a l d u r a t i o n o f c o n t ac t s :2 .2 -I-_1 .0 s p e r c h i c k ) .T h i s r e s u l t s h o w s t h a t t h e i n h i b i t i o n o f a t t a c kis m u c h m o r e s t a b l e i n t h e Tyria c a t e r p i ll a r s t h a ni n t h e p a i n t e d m e a l w o r m s . I t c a n b e a s s u m e d t h a tt h is r e s u lt s f r o m t h e t a s t e o f th e p o i s o n s , a l t h o u g ho t h e r c h a r a c t e r i s t i c s m i g h t b e r e s p o n s i b l e ( e. g . t h eh a i r s o f t h e c a t e rp i l l a rs ) . I n d i c a t i o n s o f d i s t a s t ef u l -n e s s c o u l d n o t b e o b s e r v e d e v e r y t i m e a c h i c kp e c k e d a t a c a t e r p i l la r . H o w e v e r , i n s o m e i n s t a n c e st h e y w e r e u n m i s t a k a b l e . O n e c h i c k , w h i c h h a d e a t -e n t w o g r e e n m e a l w o r m s q u i c k l y a n d p i c k e d u pt h e t h i r d w i t h a c a t e r p i l l a r l y i n g r i g h t n e x t t o i t ,s h o w e d h e a d - s h a k i n g a n d b i l l - w i p i n g f o r s e v e r a lm i n u t e s .Di scu s s i on

T h e s e e x p e r i m e n t s d e m o n s t r a t e t h a t n a i v e c h i c k sa r e i n h i b it e d i n t h e i r a t t a c k o f p r e y b y a b l a c ka n d y e l l o w w a r n i n g c o l o r a t i o n : A l t h o u g h t h e y di -r e c t t h e i r fi r s t p e c k a t b l a c k a n d y e l l o w p r e y i te m si n th e s a m e m a n n e r a s a t n o n - w a r n i n g l y c o lo u r e dg r e e n o r o l i v e o n e s , t h e y e a t t h e m a t a c o n s i d e r a b l yl o w e r r a t e . T h i s s h o w s t h a t t h e r e i s n o c o n t r a d i c -t i o n b e t w e e n M o r g a n ' s ( 18 9 6) p r o p o s i t i o n t h a tn a i v e c h i c k s p e c k a t e v e r y t h i n g w i t h t h e g r e a t e s ti m p a r t i a l i ty a n d o u r f i n d i n g t h a t t h e y e a t p a l a t a b l eb l a c k a n d y e l l o w c o l o u r e d l a r v a e l es s f r e q u e n t l yt h a n d i f f e re n t l y c o l o u r e d o n e s.

O u r e x p e r i m e n t s d o n o t e x c l u d e p e c k in g p r e fe r -e n c e s . R e a l l y M o r g a n ' s c l a ss i c s e n t e n c e i s n o t q u i t ec o r r e c t ( H e s s 1 9 7 3 ) , b e c a u s e n a i v e c h i c k s t e s t e di n l a r g e n u m b e r s p e c k a t c e r t a i n c o l o u r s ( e . g . H e s s1 9 5 6; F i s c h e r e t al . 19 7 5 ) a n d f o r m s ( G o o d w i n a n dH e s s 1 9 6 9 ) m o r e o f t e n t h a n a t o t h e r s . T h e s e p e c k -i n g p r e f e r e n c e s , h o w e v e r , c a n n o t e x p l a i n t h eb e h a v i o u r o f o u r c h i c k s , si n ce t h e y c o n s u m e dm a i n l y g r e e n l a r v a e , w h e r e a s i n t h e p e c k i n g p r e f e r -e n c e t e st s g r e e n w a s t h e c o l o u r l e a s t p r e f e r r e d .T h e r e je c t io n o f p a l a t a b l e w a r n i n g l y c o l o u r e dp r e y c o u l d b e d e m o n s t r a t e d e v e n i n c h i c k s n e v e rf e d b e f o r e . C o p p i n g e r ' s ( 1 97 0 ) n o v e l t y h y p o t h e s i s ,a c c o r d i n g t o w h i c h w a r n i n g l y c o l o u r e d i n s ec t s a r er e je c t ed b e c a u s e t h e y l o o k d i f f er e n t f ro m t h e p r e yt o w h i c h t h e b i r d i s a c c u s t o m e d , c a n f o r t h a t r e a -s o n n o t b e v a l i d i n t h i s c a s e . C o n s e q u e n t l y i t i sl e g i t i m a t e t o a s s u m e t h a t t h e i n h i b i t i o n i s i n n a t e .I t m u s t b e u n d e r s t o o d a s a g e n e t i c a l ly f i x e d p r e -d i s p o s it i o n t o a v o i d w a r n i n g l y c o l o u r e d p r e y .A n i n f lu e n c e b y f o o d w a s n o t b e o b s e r v e d i no u r e x p e r i m e n t s . T h i s d o e s n o t e x c l u d e t h e p o s s i -b i l it y t h a t o l d e r b i rd s , a c c u s t o m e d t o a v a r i e t y o fi n s e ct s p r i o r t o t e s ti n g , r e s p o n d d i f f e r e n t l y t o n o v e lw a r n i n g l y c o l o u r e d p r e y ( se e E v a n s a n d W a l d -b a u e r 1 9 8 2 ) . T h e p r o b a b i l i t y t h a t a n a i v e c h i c ka t t a c k s a m e a l w o r m c a n b e i n f lu e n c e d b y it s m o t i -v a t i o n M s t a t e ( H o g a n 1 96 5, 1 9 6 6 ) a n d b y u n s p e -c i f i c e x p e r i e n c e , e . g . b y t h e p o s s ib i l i t y t o s e e a n dp e c k a t i ts " w o r m l i k e " t o e s ( W a l l m a n 1 97 9). E v e nt h o u g h t h e s e f a c t o r s c a n n o t e x p l a i n t h e o r i g i n o ft h e i n h i b i t i o n , i t i s u n k n o w n w h e t h e r i t c a n b em o d i f i e d b y a n i n f l u e n c e o f t h i s t y p e .T h e i n h i b i t i n g , e ff ec t o f t h e b l a c k a n d y e l l o wp a t t e r n d e c r e a s e d w i t h a c c u m u l a t i n g p o s i ti v e e x p e -r i e n c e . T h e r e f o r e , a s f o r t h e s t a r l i n g s ( S c h u l e r1 9 8 2) , o n e h a s t o p o s t u l a t e t h a t t h e i n i ti a l t e n d e n c yt o r e j ec t w a r n i n g l y c o l o u r e d p r e y m u s t , f o r p e r m a -n e n t a v o i d a n c e , b e s u p p l e m e n t e d b y u n p l e a s a n t e x -p e r i e n c e . T h i s m e a n s t h a t t h e i n h i b i t i o n m u s t b eu n d e r s t o o d a s a g e n e t i c al l y f i x e d p r e d i s p o s i t i o n t ol e a r n t o a v o i d w a r n i n g l y c o l o u r e d p r e y . T h i s h y -p o t h e s i s i s s u p p o r t e d b y t h e f a c t t h a t t h e Tyriac a t e r p i l l a r s w e r e h a n d l e d o n l y a f e w t i m e s a n d a l -w a y s f o r a s h o r t p e r i o d w h e n o f f e r e d r e p e a te d l y .A l t h o u g h f u r t h e r e x p e r i m e n t s a r e n e c e s s a r y t oc l a r i fy w h i c h e f f e ct p o i s o n s h a v e w i t h o u t a w a r n -i n g c o l o r a t io n , t h is e x p e r i m e n t a l r e a d y c o r r o b o -r a t e s t h e f i n d i n g t h a t a p r e d a t o r d o e s n o t h a v et o k i ll w a r n i n g l y c o l o u r e d p r e y f o r t h e p r o c e ss o fl e a r n in g t o a v o id i t ( J f ir v i e t a l . 1 9 81 ; W ik l u n d a n dJ f i r v i 1 9 8 2 ) . T h i s i s imp o r t a n t f o r t h e q u e s t i o nw h e t h e r w a r n i n g c o l o r a ti o n s p r o t e c t via i n d i v i d u a ls e l e c t i o n .

T h e p r e d i s p o s i t i o n o f t h e c h i c ks t o a v o i d w a r n -

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254in g ly c o lou r e d b lac k ar id ye l l ow p r e y m u s t b e u n -d e r s t ood as an e vo lu t ion ar y ad ap t a t ion . T h e p r e -requis i tes for th is are fu l f i l led: First , a se lec t ionpressure can be assumed s ince ch icks which ap-p r oac h b lac k an d ye l low c o lou r e d p r e y h e s i t an t lye xp ose t h e m se lve s l es s t o t h e d an ge rs o f t h e d e f e n seo f b lac k an d ye l low n ox iou s p r ey . S e c on d , c o lou rchoice tendenc ies can be a l tered by se lec t ion assh ow n b y K o vac h ( e . g . 1978 , 1983 ). A c c or d in g t oth is idea the react ion o f other b ird spec ies to warn-in g ly c o lou r e d p r e y sh ou ld a l so b e an ad ap t e d on e :Only pat terns that are meaningfu l for the predatorin q u e s t ion sh o u ld b e e f f e ct ive an d t h e t yp e o f r e-sp on se sh ou ld b e t u n e d t o t h e p r e y ' s d e gr e e o fh ar m f u ln e s s. E ve n t h ou gh m or e w or k i s n e ce s saryto prove these hypotheses , there are a lready somer e l evan t r e su l ts : A n ad ap t a t ion o f t h e s t im u lu sp r oc e s s in g m e c h an i sm i s in d ic a t e d b y t h e f ac t t h a tb ir d sp e c i e s c om in g f r om t h e sam e ge ogr ap h ic a lr an ge a s c ora l sn ak e s sh ow in n at e avo id an c e r e ac -t ions to coral snake dummies (Smith 1975, 1977) ,w h e r e as n a ive b i r d s f r om o t h e r r e g ion s d o n o t( S m i t h 1980) . A n ad ap t a t ion o f t h e t yp e o f r e-sp on se c an b e d e r ive d f r om t h e ob se r va t ion s t h a tt h e t yp ic a l r e sp on se t o l e t h a l ly p o i son ou s w ar n -ingly coloured snakes i s f l ight (Smith 1975, 1977;C a ld w e l l an d R u b in of f 1983 ) , w h e r e as w ar n in g lycoloured insec ts , which are le ss dangerous forbirds , are sooner or later caut iously at tacked . Fi -nal ly , b ird spec ies for which warningly colouredin se c t s ar e n o t n ox iou s sh ou ld n o t h e s i t a t e t o e a tt h e m w h ic h i s su p p or t e d b y t h e f ac t t h a t you n gBee-eaters prefer b lack and ye l low pat terns(Koenig 1950) .A c k n ow l e d g em e n t s . We w ould l ike to thank Professors B . Has-senstein, E . Curio, and P. K uenz er for their encoura ging inter-es t in th is invest igat ion , Prof. K. Imm elma nn for s t imulat ingdiscuss ions , Prof. H . M arkl and two an onym ous re ferees forhe lpfu l commen ts , and Dr . E . Deusser -Schuler for cr it ica l lyreading and d iscussin g all the drafts of this paper. Furthermorewe thank Dr . H. Thorns for h in ts on obta in ing and breed ingT y r i a , G. He rwig for technical assistance, and I. Rod gers forimproving our Engl ish .ReferencesA p l i n R T , B e n n M H , R o t h s c h i l d M ( 19 6 8) P o i s o n o u s a l k a l o id si n t h e b o d y t i ss u e s o f t h e c i n n a b a r m o t h ( C a l l i m o r p h a j a c o -

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