Behavioral and Endocrine Predictors of Reproductive Success in a Cryptically Polygamous Passerine Bird

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Most birds breed as socially monogamous pairs, yet most temperate zone breeding passerines also acquire fertilizations outside of the social pair bond. It is unclear why females pursue extra-pair fertilizations, but females may acquire "good genes" that enhance offspring survival. How females identify "quality" males is uncertain, but song is known to be important in some species. Testosterone is tightly linked to male reproductive behaviors in birds, including song, and variation of testosterone might directly influence how a male is perceived by a female, but essentially nothing is known of the hormonal correlates extra-pair mating patterns and success. This research will examine the behavioral and hormonal correlates of extra-pair mating success in Eastern Kingbirds (Tyrannus tyrannus), a socially monogamous passerine in which 60% of nests contain extra-pair young. The investigators' previous work has shown that extra-pair success is directly related to song behavior, and given that song is activated and maintained by testosterone, variation of testosterone among male kingbirds is potentially directly related to extra-pair success. Hence, the goals of this project are to (a) identify the benefits to extra-pair mating behavior for females, (b) describe individual variation of testosterone among males over the season, (c) measure the relationship between testosterone and behaviors that females appear to use during mate choice (song), and (d) test the hypothesis that reproductive success is directly related to testosterone. The planned research will address important questions related to individual differences in body condition and testosterone, and determine if these differences underlie the behaviors that females use to identify quality males. The proposed research will provide graduate and undergraduate students with research experiences and further their opportunities to pursue careers in science and teaching, and through in-school programs at rural high schools, promote careers in science among young students.