DISSERTATION RESEARCH: Fitness Cost of Nest Defense: A Trade-Off With Offspring Care?

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DISSERTATION RESEARCH: FITNESS COST OF NEST DEFENSE IN A PASSERINE BIRD: A TRADE-OFF WITH OFFSPRING CARE?PI: Stephen Nowicki & Renee A. DuckworthIn many organisms, the ability of young to grow and survive depends on the care they receive from their parents. Despite the importance of parental care for offspring survival, adults often vary widely in the quantity and quality of care they provide. One of the reasons why this variation is observed may be because individuals face a trade-off in the use of their time and resources for parental care and for other activities. A fitness cost to the expression of nest defense behavior was recently documented in western bluebirds (Sialia mexicana). Bluebirds benefit from defending their nest cavities from competitors because suitable breeding cavities are a limited resource. However, male western bluebirds that defend their nests more aggressively produce fewer offspring on average each year. The proposed research examines three alternative hypotheses that could account for this observed relationship between nest defense behavior and reproductive success. Specifically, it tests whether there is a time/energy trade-off between offspring care and defense, whether aggressive males are inherently poorer parents, or whether a correlation between elevation and nest defense best explains the relationship between nest defense and reproductive success. Identifying the mechanisms that produce variation in parents' ability to raise young successfully is essential for our understanding of the evolution of parental investment strategies.