Microhabitat Factors Associated with Occupancy of Songbirds in Suburban Forest Fragments in the Eastern United States

Abstract

Forests in the eastern United States have become fragmented by urban development and agriculture, creating a landscape of remnant forest patches. Many bird species rely on these fragments for breeding habitat, but habitat selection in these patches is not well-understood. Our objective was to examine the effects of forest structure, native plants, and invertebrate biomass on the occupancy of an assemblage of common Eastern songbird species in suburban forest fragments. We collected data at 98 plots in remnant forest patches in Delaware and Maryland. Avian point counts were conducted three times per season between 15 May–7 August 2009–2010. We estimated occupancy probability, while accounting for imperfect detection, for nine common songbird species in order to understand how they are influenced by invertebrate biomass and vegetation characteristics. We ranked competing models using Akaike Information Criteria (AIC). Occupancy of six of our 10 candidate species was affected by forest structure, native plant density, or invertebrate biomass. Species we identified to have occupancy relationships with forest structure variables in suburban forest fragments appear to align well with habitat relationships that have been previously identified for the species in more forested areas. This supports that managing for structural characteristics associated with these species in more heavily forested areas could improve habitat quality for these species in suburban forest fragments as well. Occupancy of only one species we examined was related to native plants, suggesting vegetation structure, rather than composition, was a more important factor in occupancy.