Rural and suburban forest edges: effect on egg predators and nest predation rates

Although the observed declines of many species of Neotropical migratory birds have been linked to losses in the wintering grounds, it is important to examine sources of mortality from all portions of the annual cycle to fully understand migratory bird declines. Forest fragmentation and the creation of new forest edges have been implicated as factors contributing to increased nest predation rates on the breeding grounds. We selected four forests with edges in suburban settings, and four forests with edges in rural settings, to determine If nest predation rates differed with human density. From 1993 to 1994 we used two types of automatic photographic systems and artificial nests baited with quail eggs to measure predation rates on ground-and shrub nests at points 20-420 m from the forest edges. Rural-edged forests experienced significantly higher nest predation rates than did suburban-edged forests. Only three species, blue jay, raccoon, and black bear, were responsible for virtually all of the predation events. While blue jays appeared to be unaffected by forest edge type, there were more bear predations in rural-edged forests and more raccoon predations in suburban-edged forests. There were no significant differences in predation rate between nest types or in species-specific rates of predation on the two nest types. We suggest that future studies of nest predation include the identification of predators to give scientists greater insight into the predation process. Published by Elsevier Science Ltd.