||Negative impacts of forest fragmentation on migrant songbirds, habitat specialists requiring large forests to breed successfully, have been well documented. Little was known about these impacts on resident, cavity-nesting birds, species considered less affected by fragmentation. I compared reproductive variables of Black-capped Chickadees ( Poecile atricapillus ) inhabiting woodlots of varying sizes at Hawk Mountain Sanctuary. I tested for presence of edge effects, particularly nest usurpation by House Wrens. The discovery of Carolina Chickadee ( Poecile carolinensis ) haplotypes within this population added a confounding variable; however, parental haplotype did not influence nest success. Woodlot size did not influence chickadee nest success (n = 48). Chickadees chose edge over forest interior when nesting, despite increased presence of House Wrens. Earlier laying dates in smaller, edge-dominant woodlots suggest chickadees were responding to local edge effects. This was the first study to document the effects of forest fragmentation on a hybridizing chickadee population in southeastern Pennsylvania.