Meeting Abstract

20.8  Jan. 5  Seasonal social modulation of testosterone in the Costa Rican rufous-collared sparrow (Zonotrichia capensis costaricensis) ADDIS, E. A.*; BUSCH, D. S.; CLARK, A. D.; WINGFIELD, J. C.; University of Washington; University of Washington; University of Washington; University of Washington addise@u.washington.edu

Previous work has shown that birds breeding in northern temperate regions adjust production of testosterone in response to the stage of the breeding cycle and in some cases following social interactions. In contrast, studies on tropical breeding birds have suggested they regulate testosterone production in different ways. For example, the rufous-collared sparrow (Z. capensis) in Ecuador shows a pattern of testosterone level different from its northern congeners and does not increase testosterone, but does exhibit aggressive behavior, in response to simulated territorial intrusions (STI) (Moore et al. 2002). Building on that work, we investigated whether season has an effect on the social modulation of testosterone and behavior in two populations of rufous-collared sparrows in Costa Rica. Because pairs in both of these populations of birds in Costa Rica breed asynchronously, we chose to investigate social modulation of testosterone and behavior at three distinct times of year: the dry season, late March, the transition to the rainy season, early May, and the rainy season, early July. We conducted simulated territorial intrusions and collected baseline samples during these three periods. Season had a significant effect on testosterone levels and there was an interaction between season and the simulated territorial intrusion treatment, but no increase of testosterone following STI. Here we explore the physiological and behavioral results of this study, and their implications for control of breeding seasons in the tropics.