Social experience affects the process and outcome of vocal ontogeny in two populations of cowbirds (Molothrus ater).

Abstract

Longitudinal vocal records of 26 juvenile male cowbirds from 2 populations (Molothrus ater ater and Molothrus ater artemisiae) were analyzed to look for susceptibility to social influence from either female cowbirds or heterospecifics. Within each population, 1 group of males was individually housed with female conspecifics, and the other with pairs of canaries (Serinus canaria). Evidence was found for female influence in both populations. M. a. artemisiae males showed more vulnerability to heterospecific influence and developed song more slowly than did M. a. ater males. Greater vocal production was correlated with faster acquisition of song, especially for the males housed with female conspecifics. In that female cowbirds do not sing, these data indicate the inadequacy of mechanisms based on imitation to explain vocal ontogeny. The data also reinforce the need to consider the intraspecific impact of social and ecological parameters on vocal learning. The nature and the timing of vocal learning vary across populations of brown-headed cowbirds, as has been docu­ mented in laboratory and field studies (King & West, 1990; O'Logblen & Rothstein, 1993; Rothstein, Yokel, & Flei­ scher, 1986). No single pattern describes vocal ontogeny, either for songs (the focus of the present study) or for flight