Research on life history evolution in birds has revealed both direct and indirect effects of predation. Increased levels of nest predation favor reproductive behaviors that reduce the threat of predators on offspring or allow parents to bet hedge for future reproductive attempts. In this study, I investigate whether the presence of a competitor, the house wren (Troglodytes aedon), results in similar indirect effects on life history and reproductive behaviors of Carolina chickadees (Poecile carolinensis). House wrens compete for nesting cavities and will kill Carolina chickadee eggs and nestlings. I monitored nest boxes in Western North Carolina where exposure to house wrens varies. I surveyed house wren presence at active Carolina chickadee nests and measured clutch size and mass, incubation, provisioning rates, nestling growth rates, development, and fledging success of chickadees. House wren takeover accounted for 35% of nesting failures, more than any other cause of failure in our study. I found smaller clutch sizes in areas where house wrens were present. However, I did not detect any effects of house wren presence on chickadee egg size, incubation, provisioning, growth, or development. These results suggest that house wren presence affects a narrow range of life history traits early in the nesting period, possibly because this is when house wrens are the biggest threat. Reducing clutch size may be a strategy used by Carolina chickadees to decrease reproductive investment in an environment where early nest failure is probable, allowing adults to reserve energy for survival to the next breeding season
