Knowledge of the relative contributions of predator species to overall rates of nest predation can improve our understanding of why predation risk varies, but the identity of predators is seldom known. We used video technology to identify nest predators of the tree-nesting Acadian Flycatcher (Empidonax virescens) and the shrub-nesting Indigo Bunting (Passerina cyanea) in forests of Missouri and southern Illinois. Raptors, snakes, and nonraptorial birds were the most frequent nest predators; rodents depredated fewer nests; and mesopredators rarely depredated nests. We tested hypotheses concerning effects of songbird species, ordinal date, nest stage, height, and age on overall and predator-specific predation rates to determine whether variation in overall predation rates was attributable to a subset of nest predators. Overall predation rates were higher for Indigo Buntings than for Acadian flycatchers, were higher during the nestling stage than during incubation, and exhibited a midseason peak. Compared with Indigo Buntings, Acadian Flycatchers experienced significantly lower predation by raptors, nonraptorial birds, and snakes and were never depredated by a mesopredator. Nests of both species had higher predation rates during the nestling stage than during incubation because of increased predation by raptors and snakes. Raptors, nonraptorial birds, snakes, and rodents all exhibited a midseason peak in predation rates. Estimating the contribution of specific predators to overall predation rates can increase our mechanistic understanding of why predation risk varies and thus improve our understanding of antipredator behavior and increase our ability to predict how anthropogenic habitat and climate change will influence avian productivity.
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Vol. 129 • No. 1