The occurrence of three reproductive tactics in a population of American redstarts was estimated: extra-pair fertilization, egg-dumping, and male polyterritoriality. Using DNA fingerprinting we show that none of 108 nestlings samples were the result of egg dumping. In contrast, 40% of nestlings were the result of extra-pair fertilizations. Males sired a greater proportion of their broods as they aged. In addition, promiscuous females were never fertilized by males that were younger than their social mates. Whether the poor reproductive performance of younger males was caused by female preference for older males or by intra-sexual competition was not determined. In any case, females would have benefited by mating with older males, if the traits that allowed the survival of the father were inherited by the females' offspring. Only three of 80 males attracted two females through polyterritoriality. One male fledged two broods: he sired both nestlings from his first brood, but none of the four nestlings from his second brood. We concluded that male redstarts can improve their reproductive success by trying to obtain extra-pair copulations, but less so by establishing a second territory.

This research examined how song is used to transmit information on individual identity in American redstarts (Setophaga ruticilla). Specifically, it attempted to determine whether American redstarts (1) discriminate between neighbors and strangers on the basis of their respective songs, and (2) recognize individuals by their distinctive voice characteristics. I tested the latter by exposing subjects to identical song types sung by different birds. Each subject's behavior was evaluated according to a variety of response variables. In all trials, for all response variables, subjects responded highly but equally to each of the songs played. A post-hoc analysis revealed that the order in which treatment songs were presented affected the birds' responses. For four of five response variables, subjects successfully distinguished between the songs of neighbors and strangers when played the fourth song in the trial. Thus, it would appear that in redstarts this type of discrimination may be observed only after an initial song-exposure period.

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