Bird song has been shown to be important in both inter- and intrasexual selection. Elaboration of the latter trait has been studied extensively. I conducted a field experiment to investigate the role of song in territory establishment of the Prothonotary Warbler (Protonotaria citrea). Songs were recorded for 31 males and song parameters were regressed against dates of territory acquisition, territory size, and territory location. In addition, feeders were placed in the territories of 17 randomly selected males. Song recordings from these males over the entire breeding season were compared with a reference group of 14 males. Males that sang more frequently acquired territories in preferred locations and earlier in the breeding season. A significant change occurred in song rate over the breeding season for males provided supplemental food. These findings suggest that physiological condition constrains song parameters that are important in territory establishment in the Prothonotary Warbler.