Non Technical Abstract 9728091 Rothstein, S. I. This project employs integrated field and laboratory approaches to investigate the development of vocal behavior in a common songbird, the Brown-headed Cowbird. Major emphases are elucidation of the ecological conditions that limit or enhance learning processes and the concordance between (1) the development of female recognition of male song and (2) the development of male song production. Goals will be pursued by studying wild birds under different ecological conditions and by bringing birds into captivity for short periods to study song structure and function. The cowbird is important to the study of animal behavior and ecology for several reasons. The extensive amount of prior work on it has made it a model for studies of vocal development in songbirds, which is remarkably similar to speech development in humans. However, much of the prior work has been limited to captive birds and may not reflect learning processes that occur in nature. In addition, this species is a brood parasite whose young are raised by a host species but nevertheless overcomes this early behavioral deprivation and learns only cow-bird vocalizations. Besides serving as a model for behavioral development in the face of early deprivation, the cowbird is also significant to endangered species and to the preservation of biodiversity. Other species may divert so much of their parental effort towards raising cowbirds that they sometimes raise too few of their own young to ensure the persistence of host populations. The basic knowledge gained in this study may lead to improvements to the extensive and very costly management efforts currently employed to ameliorate the impacts of cowbird parasitism.