Lower Begging Responsiveness of Host Versus Parasitic Brown-Headed Cowbird (Molothrus ater) Nestlings Is Related to Species Identity but Not to Early Social Experience

The survival of young brood parasites depends critically on their many adaptations to exploit hosts. Parasitic survival is particularly related to competitive superiority for foster parental care whenever host young are not destroyed in parasitized nests. Brown-headed cowbirds (Molothrus ater) are generalist obligate parasites whose early social environments are unpredictable regarding host species and numbers of nestmates. Young avian brood parasites typically beg more intensively and loudly than foster siblings, but an untested prediction is that young parasites are also more likely to respond by begging to a wider variety of stimulus types. Avian vocalizations were used in a playback experiment to stimulate begging behavior in cowbird hosts. Compared with age-matched cowbird nestlings, hosts begged less frequently to acoustic stimuli, and lower begging responsiveness was irrespective of whether hosts had been reared in parasitized nests.