Reproductive success of forest-dependent songbirds near an agricultural corridor in south-central Indiana

Potential source populations of forest-brooding Neotropical migrant birds m ay be threatened by anthropogenic changes that increase brood parasitism by Brown-headed Cowbirds (Molothrus ater) and nest predation in heavily fores ted breeding areas. In southcentral Indiana, corridors of agriculture and r ural development, ranging from < 50 m to several thousand meters in width, penetrate interior portions of the heavily forested landscape. These corrid ors provide habitat for cowbirds and nest predators. We monitored breeding success of six species of Neotropical migrants and one resident species nea r an agricultural corridor and in interior forest. We found that nest survi val was lower near the agricultural corridor for most of the species in the nestling stage, but no consistent difference in nest survival was detected during the egg stage. Levels of cowbird parasitism were generally elevated near the agricultural corridor. Estimates of the number of fledglings per nesting attempt indicated that seasonal productivity was lower near the agr icultural corridor for six of the seven species. Status of populations of b irds in south-central Indiana as sources in the Midwest may be compromised by extensive intrusion of agricultural corridors within the contiguous, hea vily forested landscape.