LTREB: Role of winter sociality in the evolution of facultative social behavior

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

PI: Janis L. Dickinson Proposal # 0097027 Proposal Title: The role of winter sociality in the evolution of facultative social behavior This is a proposal to continue a long-term study of a color-banded population of western bluebirds whose sons exhibit remarkable behavioral plasticity in the form of staying with parents for winter, breeding on their own, helping at their parents' nest, and feeding at nests of widowed females. The specific aim of this study is to determine the benefits for young males remaining on their parents' territory through the first winter, a behavior that is a necessary precondition for further interaction with parents later in life. Mistletoe berries are a stable winter resource that is key to year-round territorial behavior in this system. An experiment that involves removing half the mistletoe from winter territories will determine the impact of mistletoe abundance on whether sons stay, their condition, and their success at acquiring a mate and breeding territory of their own. The alternative hypothesis, that sons benefit by staying home due to the preferential treatment they receive when they remain with parents, will also be tested. In fact, both access to parental resources and preferential treatment by parents may simultaneously explain why sons remain home. This work is novel because mistletoe is a uniquely manipulable food resource and its availability only during winter allows for a clean separation of the importance of winter food for dispersal and family stability in a species with year-round territories. Although the results of this study will address a basic question in evolutionary behavioral ecology, they will also address an issue of potential importance to the decline of western bluebirds in California. If mistletoe quantity proves critical to the tendency for young males to stay home for winter and reduction of mistletoe has negative impacts on the condition and survival of stay-at-home sons, then we will have identified a key environmental variable regulating bluebird populations in California.