THE AUK A QUARTERLY JOURNAL OF ORNITHOLOGY VOL. 78 OC•'OBER,1961 NO. 4 INTERSPECIFIC PREENING INVITATION DISPLAY OF PARASITIC COWBIRDS ROBERtK. SELA•DERA•D CHARLESJ. LA RUE, JR. BROODparasitism holds special interest for the student of behavior, sinceadoption of this highly specializedway of life, which has evolved independentlyin five avian families (Miller, 1946), involvesnot only the lossof nestingand parentalbehavior but also the developmentof a complexof new patternsof behavioradapting the parasiteto the host. Specializationfor parasitismis most marked in the European Cuckoo (Cuculus canorus) and related forms of the subfamily Cuculinae (Chance, 1940) and perhapsleast so in the cowbirds(Icteridae) of the New World, which have very closelyrelated, nonparasitic relatives and havehad a comparativelyshort evolutionaryhistory as parasites(Fried- mann, 1929, 1955). A considerablevolume of informationon cowbirds has beenprovided by the pioneerwork of Frledmann (1929) and later studiesby Nice (1943), Harm (1941), Norris (1947), Laskey (1950), Mayfield (1960, 1961a and b), and others,but we are still far short of an adequateunderstanding of the biologyof thesebirds. In particu- lar, the complex behavioral interactions occurring between parasite and host, both at the time of egg laying by the cowbird and during the course of developmentof the cowbird in the care of the foster parents, are essentiallyunknown. Early in the courseof studieson the behaviorof the Brown-headed Cowbird (Molothrus ater), beginningin February 1959, we noted that captive cowbirds persistently approached individuals of certain other speciesof birds and invited heteropreeningof the head and neck by adopting a special head-bowedposture (Figure 1). Surprisingly enough, repeated presentationof this display was often effective in inducingother speciesto preen the cowbirds'plumage. Subsequently, we obtained a number of field records of this behavior in Brown-headed Cowbirds,and a similar displaywas seenin captiveRed-eyed Cowbirds (Tangavius aeneus). It would seem, therefore, that heteropreening invitation is a regular, althoughhitherto unstudied,part of the behavioral 473 [ .Auk. 474 SELANDERAND LA RUE,Preening7 Display of Cowbirds [Vol.78 repertoire of these parasitic icterids. The behavior is all the more unusualin that cowbirdsonly infrequentlydirect the invitationaldisplay to membersof their own speciesand do not themselvesindulge in social heteropreening. The presentreport dealsalmost entirely with preeninginvitation in the Brown-headed Cowbird, and, unless otherwise indicated, the term "cowbird" refers to that species. It is our hope that this paper will stimulateother workers to observeand report further instancesof the use of this displayby cowbirdsin the field, sincethe significanceof this behaviorcan be judgedonly when an abundanceof field recordsis available. DISCOVERY OF TIlE DISPLAY The display was first seen on 27 February 1959, while we were observinga group of 22 Brown-headedCowbirds in a large, outdoor aviary. A malecowbird approached a femalecowbird and displayed,at which point the femaleflew. Later in the day, a male directeddisplay to another male resting on a perch; and, as the displayingbird ap- proached,the resting bird peckedit away. When this behavior was first observed,we suspectedthat it repre- sentedan intraspecificdisplay in someway associatedwith courtship or pair formation. However, this suppositionproved to be erroneous, and the normal use of the displaybecame apparent when other species of birds were placedin the aviary with the cowbirds. On 3 March, a few minutes after a meadowlark (Sturnella) was introduced, several cowbirdsapproached it and displayed. At first the meadowlarksimply retreated to a new position, often flying to another perch, at the ap- proach of the cowbirds; but, later the same day, we •oted that the meadowlarkwas less prone to flee and now often remainedin a fixed position,pecking at the cowbirdsas they displayed. Next day, the meadowlarksometimes responded to the displayby preeningthe cow- birds rather than fleeing from them. And for a period of two weeks during which the meadowlarkwas confinedwith the cowbirds,preening becamethe usualresponse of the meadowlarkto any cowbirdin display. As a consequence,the meadowlarkwas "victimized"to the extent that it spentseveral hours each day in this activity. In late March, several female Red-winged Blackbirds (.4gelaius phoeniceus)were placed in the aviary, where they remained through the summer and fall. A day or two after their introduction, they were seen to preen displayingcowbirds, and this behavior was noted hundreds of times in the following months. Octoberl1961 .I SELANI)ERANI) LA RUE,Preening Display o! Cowbirds 475 DESCRIPTION OF THE DISPLAY We have usedthe term "display"for this behaviorsince it involves distinctivepostures and movementshaving obvious communication function,inducing, normally, flight, attack, or heteropreeningin the individualto which it is directed,hereafter called the recipient. display (Figures 1A, lB, and 1D), the head is bowedto a point at which the bill is directedeither verticallydownward or in toward the cowbird'sbody. The feathersof the head and nape are conspicuously ruffed, but other body plumage is generally slightly compressedor sleeked. The wings and tail are held in normal resting position,and the cowbirdis often slightlycrouched. Assumptionof the head-bowedposture is accompaniedor shortly followedby a movementof the cowbird toward the recipient. This may be a sidling motion along a perch or a direct head-onapproach. Usually the cowbird halts when its head is about one inch from the recipient,but the approachmay continueuntil the top of the cowbird's headis actuallyplaced against the breastof the recipient (Figure 1A). Orientationof the cowbird'sbody with respectto the recipient'sposi- tion varies: frequentlythe body is oriented along a perch as frontal Figure 1A. Male eowbird gives preening invitation to female Red-winged B!aekbird. 476 SELi•DER,•D L^ RUE,Pree•i•9 Display o] Cowbirds tVol.[ Au•. 78 ,I Figure lB. Female cowbird invites preening from a Shell Parakeet. ½ Fi&•re IC. Displayingfemale cowbirddodges peek by Shell Parakeet. October]1961 J SELANDERAN• L^ RUE,Preening Display of Cowbirds 477 presentationof the head is made (Figure lB), but cowbirdsalso posturewith the body at an angle,often about45 ø , to the recipient. Or the cowbirdmay perchside-by-side with the recipient,bowing the head and cockingit toward the recipient. Oblique presentationsare most likely to be usedwhen the recipientis in the habit of peckingat the displayingcowbird; this permitsthe cowbirdto dodgethe blows by turning rapidly away (Figure 1C). Regardlessof the orientationof the displayingcowbird's body, the cowbirdpostures in a positionin whichthe occipitalregion of the head is directedtoward the head of the recipient. While presentingthe fluffedfeathers of the head,the cowbirdmaintains a rigid pose,avoiding rapid or suddenmovement; and it avoidsdirect visualfixation of the recipient. In the displayingcowbird, the eyeshave a characteristic "glassy"appearance. The displayis not accompaniedby vocalizations. Displayis givenon perches,on the ground,or whileboth the recipient and the cowbird cling to the wire sides of an aviary or cage. If heteropreeningis induced,the cowbirdmaintains the bowedposture and continuesto avoid suddenmovement, although it may make slight changesin positionof the head,as if to encouragethe respondingre- cipientto preen particularregions. THE DISPLAY IN CAPTIVE ]•IRDS All our observationsof the preeninginvitation display in cowbirds confinedto aviariesand cageshave involvedadult and first-year indi- Figure 1D. Male cowbird displays to dummy V•hite-crowned Sparrow. 478 $•^NDERAXeD LA RyE,Preening Display o] Cowbirds Vol.Auk.78 viduals capturedin the spring in the Austin region, Texas. We have not yet had an opportunityto study this behaviorin juveniles or in immature individualsless than six monthsold; but JamesBaird (pers. comm.) has observedthe display in a two-month-oldjuvenile female held in a cage with a female Red-wingedBlackbird. INTRASPECIFIC PRESENTATION As we have indicatedpreviously, a cowbirdonly occasionallydirects the displayto anothermember of its own species. In severalhundred hoursof observationof severalgroups of cowbirdsconfined to aviaries and cagesin the absenceof individualsof other species,we have noted intraspecificpresentation of the displayon no more than 25 occasions. Our records indicate that it is most likely to occur among cowbirds that have beendeprived of contactwith other speciesfor long periods. Also, the frequencyof intraspecificpresentation usually rises for a brief period following the introductionof an individual of another species. In all recorded instancesof intraspecificpresentation, the display was given only a singletime and invariably resultedin withdrawal or Figure IE. Agoniztic behavior of two male cowbirds, each intent on soliciting preening from d•mn•y •Vhite-crowned Sparrow. The bird on the left is beginning ruff-out display as the other bird gives head-up display; both displays have threal function. Octoberl1961 I SF_.LAI•DERA•V I• RuE,Preening Display of Cowbirds 479 Figure IF. Male cowbird at height of ruff-out display to dummy White- crowned Sparrow. attack on the part of the recipient cowbird. Most frequently the recipient cowbird pecked at the displaying cowbird as it approached, and this brought an end to the episode. In no instance did intra- specificpresentation