Eastern bluebird (Sialia sialis) populations are increasing across most of the species' range; however, we document a decline in a bluebird population in central Kentucky, where state and local Christmas Bird Count and Breeding Bird Survey data indicate bluebirds are declining throughout the Ohio River valley region. We examined several possible hypotheses for this decline, including habitat loss, nest cavity loss, increased competition from other species, and variation in winter temperature using long term nesting data gathered at one study site in central Kentucky. We found that bluebird abundance was positively correlated with mean temperature during the previous winter. Our data suggest bluebirds in central Kentucky are declining because they are susceptible to cold winters and are experiencing increased nest box competition.