Quantifying male Wood Thrush nest-attendance and its relationship to nest success

Male Wood Thrushes (Hylocichla mustelina) attend their nests by perching near its rim, a behavior common to many species and presumed to be for the purpose of guarding eggs or young in the nest. We classified nests into two groups based on whether or not we observed an attending male during any nest inspection. We found that nests attended by male Wood Thrushes had higher success rates (i.e., lower predation rates) than unattended nests in Illinois where Blue Jays were a dominant nest predator. In contrast, there was no significant difference in nest success between attended and unattended nests in New York where rodents (mice and chipmunks) and raptors, such as the Sharp-shinned Hawk, were important predators on nests and adults, respectively. Despite differences in risk to adults and nests between the two sites, the frequency of observing attendant males did not differ between sites. In contrast to studies in the literature, the frequency of nest-attendance in the New York population was negatively related to year-to-year variation in chipmunk density, an independent measure of the risk of nest predation.