Stimulatory effects on the reproductive axis in female songbirds by conspecific and heterospecific male song

Courtship vocalizations of male songbirds can profoundly enhance the reprod uctive physiology and behavior of conspecific females. However, no study ha s fully investigated the selectivity of conspecific song effects on reprodu ctive development in birds. We studied the effects of conspecific and heter ospecific song on reproductive development in domesticated (canaries) and w ild songbirds (song sparrows). As expected, conspecific song enhanced folli cular development. Unexpectedly, however, birds exposed to heterospecific s ong also underwent enhanced follicular development (compared to birds expos ed to no song); conspecific and heterospecific songs were equally effective in enhancing ovarian development. In canaries exposed to 18L:6D, conspecif ic song induced oviposition earlier and at a greater frequency than in hete rospecific and no song groups, with the fewest eggs being laid in the no so ng group. These results indicate that conspecific and heterospecific male s ong can enhance reproductive activity in female songbirds. Whether or not a ctivation of the reproductive axis in female songbirds by heterospecific so ng occurs in the wild remains unclear. It is also unclear as to whether the ability of the reproductive axis to respond to heterospecific song perform s a specific function, or whether it is simply a consequence of greater sel ection pressure acting upon behavioral responses to song. (C) 2000 Academic Press.