Local changes in a breeding bird community following forest disturbance

Species composition and population sizes of breeding birds changed substantially in less than 10 yr following local disturbances in a mixed deciduous forest plot in Itasca State Park, northern Minnesota. Dutch elm disease, drought, and windstorms changed a closed-canopy elm-birch-ash forest to a more open habitat dominated by basswood, ash, and standing snags with large areas of dense fern cover. Breeding bird censuses conducted in 1979-1981 and 1990-1992 showed substantial changes in local populations of several species including Ovenbirds (Seiurus aurocapillus) (20.0 territories/10 ha in 1979-1981 to 1.6 in 1990-1992), Veeries (Catharus fuscescens) (4.1 to 0.9), Mourning Warblers (Oporornis philadelphia) (0.7 to 5.5), Song Sparrows (Melospiza melodia) (0.0 to 6.4), and White-throated Sparrows (Zonotrichia albicollis) (0.0 to 7.1). These changes were related to increased density of ground vegetation and increased light levels. Spatial distribution of species showing major increases was strongly associated with the locations of patches of dense undergrowth. Arboreal species showed less population change between census periods than did ground foragers. These local population changes were unrelated to trends over the same period on a 15-km roadside survey in the park. Changes in species abundance on the plot appear to be caused by local habitat change rather than broader-scale processes.