A role of her own: female cowbirds, Molothrus ater, influence the development and outcome of song learning

Previous work has:shown that captive female cowbirds, Molothrus ater, can i nfluence the outcome of male song development by affecting retention or del etion of song elements and by stimulating improvization. Here we looked far evidence of female influence during the process of learning, as males prog ress from subsong to plastic song to stereotyped song. In a longitudinal st udy, we measured the rate and timing of vocal development in captive, juven ile male brown-headed cowbirds, M. a. artemisiae. Half the young males were housed with female cowbirds from their own population (South Dakota: SD) a nd half with female cowbirds from a M. a. ater population (Indiana: IN). Bo th populations of females prefer local songs and differ in the time of bree ding, with SD females breeding 2 weeks later than IN females. The results s howed significant effects of female presence on the age at which males adva nced through stages of vocal development: the SD males with SD females, as opposed to SD males with IN females, developed stereotyped song earlier, re duced motor practise earlier, and produced more effective playback songs. L ongitudinal observations of social interactions showed that the two groups of females reliably differed in social responses to males. Degree of social proximity of females to males in the winter predicted song maturity, rate of rehearsal and song potency. Thus, females can stimulate the progression of song learning, as well as prune song content. (C) 2000 The Association f or the Study of Animal Behaviour.