VoL,94057] a l_•caz,Courtship Feeding in Birds 169 COURTSHIP FEEDING IN BIRDS BY DAVID LACK INTRODUCTION IN many differentgroups of birds the male feedsthe female during courtshipor incubation. The literature on this point is large and scattered. The objectof the presentpaper is to summarizethe data so far as I have been able to collect them. So many instanceshave been reportedin worksdealing primarily with other mattersthat I cannothope that the presentlist of birdsis nearlycomplete. Indeed, one of the objectsof this paper is to stimulate others to record in- stancesfrom typesof birds not recordedhere. Someyears ago cor- respondentsof 'The Auk' greatly increasedour knowledgeof the extentof' injury-feigning'in birdsand in this,as in courtshipfeeding, an accurateknowledge of all thosegroups in which it occurs,and also of thosein which it doesnot occur,greatly assistsin interpretingthe significanceof the habit. Beforepublication, I am sendingthis paper to Mrs. Margaret M. Nice with the requestto add all the casesthat shemay know from her unrivaled knowledgeof the literature of bird courtship. Indeed,should the Europeansituation make it impossible for me to seethe proofsof the paper,I am askingMrs. Nice to super- visepublication. i must alsothank Dr. E. Mayr and Dr. G. K. Noble for their help in discussion. MANNER OF FEEDING In mostcases of courtshipfeeding, the femaleadopts an attitudeand callsalmost identical with thoseof a youngbird beggingfood from its parents,and the male puts food into the œemale'smouth. x In some birds,the male simplycollects the food in his beak and then presents it to the œemale;in others,notably in someFringi1Iidae (i.e. Car- duelinae)and gulls, the male regurgitatesthe food to the female, as he alsodoes when feedingthe young. While this is the normal pro- cedurethere are a few variations. Thus in the Herring Gull and other gulls, the male regurgitatesthe food on to the ground in front of the female, and the female then swallowsit. In terns, presentationof food is often precededby a ceremonialflight. In somebirds of prey, • Monika Holzapfel in her 'Analyse des Sperrens, und pickens in der Entwicklung des Stars' (Journ. f. Ornith., 87: 5•5-553, '959) suggeststhat 'gaping' for food is not merely a juvenal phenomenon,but that it is replaced by the tendencyto peck for food, and becomeslatent, reap- pearing later in those specieswhere the male feeds his mate.--M. M. N. 170 LACK,Courtship Feeding inBirds I.[' AukApril notablyCircus, the food is passedfrom the male to the femalein the air, the female turning over to catch it. In the Ad61iePenguin (Pygoscelisadeliae) the male brings not food but snow to the incu- bating female. Dr. Mayr drawsmy attention to Gallus gallus do- mesticus,which does not presentthe femalewith food, but scratches the groundup for her (asa hen doesfor her chicks). T•-IE R6ta•s ov X•-IE SEXES In nearly all birds it is the male which feedsthe female. The re- spectiver6les of the two sexesare almostas constantas are the posi- tions adoptedin copulation. A partial exceptionis the waxwing (Bombycilla),in which male and femaleexchange food backwardand forward, but it is again the male which first presentsand the female whichfirst receives the food. ! onceobserved the samein Platyspiza crassirostris,one of the Galapagosfinches, but here it is very unusual, and! haveseen it once (out of hundredsof cases)in the BritishRobin (Erithacusrubecula melophilus), when the birds were disturbedby a mount near the nest. In one bird, the Button Quail, Turnix, the normal procedureis reversedand the femalefeeds the male. This wasperhaps to be ex- pected, since in Turnix nearly all the sex behavior is reversed. In Common Terns (Sterna hirundo), Tinbergen recordsthat, in the early stages,either sex may beg for or presentfood. Under artificial conditionsin captivity,I have had a female British Robin feed another female, and a male beg food from a female. Why, normally,the male shouldgive the food and the femalere- ceive it, and not the reverse, is far from clear. The occurrence of the oppositein Turnix, whereother sexbehavior is alsoreversed, is con- firmation that there is a fundamental distinction between male and femalein this matter. Possiblyit is relatedin someway to the phe- nomena classified under the term 'dominance,' but ! am not too happyas regardsthe useof this latter term owingto its subjective implications. The captivity recordsof the British Robin show that the behaviornormally found in one sexis latent in the oppositesex (this seemsto apply to all phasesof sexualbehavior in birds). SIGNIFICANCE OF THE FEEDING In many speciesin which courtshipfeeding occurs, the male also feedsthe femaleon or near the nestduring incubation. Hence,at thisstage of the breedingcycle, the foodmay have real significance. Vol.•04o57 •] LACK,Courtship Feeding inBirds 171 Indeed, there probablyexist speciesin which the feedinghabit is restrictedto the incubationperiod. In this case,it could not be classedas courtshipfeeding at all. I know of no fully established cases,but thismay well occurin someof the speciesgiven in the table laterin whichthere are records of feedingonly during incubation, e.g., sometitmice (Paridae),some finches (Fringillidae), some crows (Cor- vidae). However,there are alsosome species, e.g., Aix sponsa,Gallus and Turnix (? alsoCentropus and Coccyzus)in whichthe feedingof thefemale by the maleoccurs in courtshipbut apparentlyceases before incubation. Further,in manyof the speciesin whichthe male feeds thefemale during incubation, feeding is alsoregular before incubation and in somespecies, e.g., the British Robin, it is much commoner beforethan duringincubation. Hence,in theselatter birdsthe main functionof courtshipfeeding is clearlydisplay. Clearlythe primaryobject of courtshipfeeding is not the foodwhich is passed.Numerous cases could be citedto showthis. I mayquote Goethe0937), that a femaleHerring Gull (Larusargentatus) just returnedfrom feedingon the shore,and, therefore,presumably well fed, may beg her mate for food although he has remained near the nest and has not fed recently. Again, in captivity a female British Robin would often beg her mate to feed her thoughshe was standing on the food tray, surroundedby live mealworms,and he was some distanceaway. Again, in Bombycilla,the food is passedback and forth betweenthe sexesand finally is often eaten by the male. In somespecies, courtship feeding seems closely associated with cop- ulation. Thus, in Centropusjavanicus the male holdsan insectin its beak during copulationand feedsthe femaleimmediately after- ward. In the Yellow-billedCuckoo (Coccyzusamericanus), the male alsoheld an insectduring copulation, and, towardthe end,the female slowlyturned her headand took and ate it. In Carnarhynchuspar- vulus,one of the Galapagosfinches, Mr. W. H. Thompsonsaw the malefeed the femaleduring copulation. Again,in the Herring Gull, Goetherecords that the initiatory stagesof copulationare closelysimi- lar to thoseof the male feedingthe female. In Columbalivia, the male feeds the female before copulation. In the European Nut- hatch (Sitta europaea),courtship feeding and copulationare also saidto be correlated,and this may be the casein Gallusgallus domes- ticus. The associationof courtshipfeeding with copulationin the above speciesseems clear, and thisapplies to someother species. However, 172 LACK,Courtship Feeding inBirds LAprilFAuk there are other birds in which there is no connection between court- ship feedingand copulation. This is clearly the casein the British Robin, in which courtshipfeeding and copulationoccur quite inde- pendently,and whereascopulation is restrictedto a very limited period duringnest building and egglaying, courtship feeding occurs through- out the breedingcycle except when the birds are feeding the young. This was alsotrue for the Galapagosfinches except for the one case in Carnarhynchusparvulus, already reported (D. Lack and W. H. Thompson);it applied to Spinuslawrencei (D. Lack) and evidently appliesto manyother species,since the observers•make no recordsof any connectionwith copulation. Further data are desirablebut it seemsprobable there are more speciesin which the habit is not con- nectedwith copulation,than thosein which it is. The functionof courtshipfeeding in the latter formsis presumably to maintainthe bond betweenthe pair, whichis especiallyimportant in birds in which both sexesfeed the young. In this connectionit seemssignificant that courtshipfeeding is found mainly in birds in whichboth sexescare for the young. This is especiallysignificant in thosegroups of birds which includeboth somespecies which remain paired,and somewhich do not form a pair bond. Thus, in the gal- linaceousbirds, the Bob-white(Colinus virginianus) remains paired and courtshipfeeding occurs, whereas it doesnot occurin the many gallinaceousbirds where no pair bond is formed. Again, in the cuck- oos (Cuculidae),it occursin Centropusand Coccyzus,but not (so far asknown) in the parasiticforms. There are,however, exceptions to this rule. Thus in Turnix, the female leaves the male soon after incubation has commenced. OTHER FEEDING HABITS This habit of onebird feedinganother seems normally part of court- ship. However,two casesare reported by Murphy in whicha Fregata rnagnificensand an adult Brown Booby (Sula leucogaster)at least four yearsold, were found in perfectcondition at breedingcolonies, althougheach possessed only one wing and couldnever have captured food for itself. Both birdsapparently retained the food-beggingbe- haviorof the youngand