A password for species recognition in a brood-parasitic bird

Recognition of conspecifics is an essential precursor of sexual reproductio n. Most mammals and birds learn salient features of their parents or siblin gs early in ontogeny and later recognize individuals whose phenotypes match the mental image (template) of relatives closely enough as conspecifics. H owever, the young of brood parasites are reared among heterospecifics, so s ocial learning will yield inappropriate species recognition templates. Init ially, it was inferred that conspecific recognition in brood parasites depe nded on genetically determined templates. More recently it was demonstrated that learning pla)is a critical role in the development of parasites' soci al preferences. Here we propose a mechanism that accommodates the interacti on of learned and genetic components of recognition. We suggest that conspe cific recognition is initiated when a young parasite encounters some unique species-specific signal or 'password' (e.g. a vocalization, behaviour or o ther characteristic) that triggers learning of additional aspects of the pa ssword-giver's phenotype. We examined the possibility that nestlings of the obligately brood-parasitic brown-headed cowbird (Molothrus ater) could use a species-specific vocalization, the 'chatter', as a password. We found th at six-day-old nestlings responded (begged) significantly more frequently t o playbacks of chatters than to other avian sounds and that two-month-old f ledglings approached playbacks of chatters more quickly than vocalizations of heterospecifics. Free-living cowbird fledglings and adults also approach ed playbacks of chatters more often than control sounds. Passwords may be i nvolved in the ontogeny of species recognition in brood parasites generally .