Differences in Song Rate in Two Populations of Yellow Warblers

—The Yellow Warbler (Dendroica petechia) has a mating system characterized by monogamy and biparental care, and has the broadest breeding distribution of any Dendroica species. When faced with a short breeding season and unpredictable conditions at high latitude, they display physiological responses to help optimize the tradeoff between individual risk and reproductive success. Because these circumstances may also affect behavior, we measured the song rates (songs/hr) of subArcticand temperatebreeding males during the nestling period. Temperate males sang at higher rates when compared to subArctic males. Maintaining a high song rate while provisioning nestlings may be advantageous if a second brood is attempted. Our results suggest behavioral plasticity as a result of differing constraints on time and reproduction. Received 3 April 2006. Accepted 28 August 2006. The Yellow Warbler (Dendroica petechia) has the broadest breeding distribution of any Dendroica species (Dunn and Garrett 1997, Lowther et al. 1999) and occurs in high density over much of its range (Sauer et al. 2001). This species’ mating system is characterized by monogamy and biparental care, but extrapair mating (Yezerinac and Weatherhead 1997, Yezerinac et al. 1999) and polygyny have been documented (Ford 1983, 1996; DellaSala 1986; Reid and Sealy 1986; Spector 1991). Such deviations from the typical mating system may occur mainly at lower latitudes, because the brief northern breeding season enforces increased nesting synchrony and reduces opportunities for extra-pair interactions when compared to more temperate populations (Briskie 1995, Yezerinac et al. 1999). We earlier demonstrated that males breeding at high latitude display a significantly re1 Department of Biology, University of Mississippi, University, MS 38677 USA. 2 Current address: Department of Biology, Hollins University, Roanoke, VA 24020 USA. 3 Current address: Department of Biological Sciences, University of Maine, Orono, ME 04469 USA. 4 Corresponding author; e-mail: mwilson@hollins. edu duced endocrine response to stress during nestling provisioning (when compared to temperate-breeding males) to help optimize the tradeoff between individual risk and shortterm reproductive success (Wilson and Holberton 2004). In the present study, we investigated whether corresponding behavioral plasticity occurs in the timeand energy-demanding behavior of singing. We predicted that subArctic-breeding males would spend less time singing during the nestling period when compared to their temperate counterparts, particularly late in the nestling period, when energetic demands of their growing nestlings are highest. Temperate-breeding males also have demanding nestlings during this stage, but we predicted they would be less constrained by parental care and more likely to continue defending territories and females in preparation for a possible second breeding attempt.