Despite much interest in the conservation of landbirds during migratory stopover periods, relatively few studies have examined spatial and temporal variation in habitat use and identified important habitats for migrating landbirds in North America. We surveyed migrant landbirds in five habitats (mature forest interior, mature forest-agricultural edge, mature suburban forest, mid-successional pole-stage forest, and early successional shrub-saplingstage forest) in central Pennsylvania from late August to early October, 1997–1999. We used abundances of individual species and migrant guilds, species richness, and fruit availability to assess relative habitat quality for fall migrants and measured structural characteristics associated with migrant habitat use. Of 15 species that differed in abundance among habitats, species that breed in mature forest (n = 10) were typically broadly distributed among habitats during stopover, with highest abundance in edge-dominated forests (forest-agricultural edge and suburban forest) and lowest abundance in pole-stage forests. Mature-forest-breeding migrants also regularly used early successional forests, where as many individuals were recorded as in forest interior. Shrub-sapling-breeding species (n = 5) generally were more narrowly distributed among habitats and were most abundant in early successional and edge-dominated forests. We detected among-year differences in relative use of habitats by mature-forest-breeding species, which suggests that the relative quality of stopover habitats may vary from year to year. Fruit availability was highest in shrub-sapling and forest-agricultural edge habitats and was positively associated with abundance of primary frugivores in all three years, indicating that fruit may be driving habitat selection by that guild. Mature-forest-breeding migrants were positively associated with forests that had more understory vegetation and lower percentage of canopy cover (i.e. more tree-fall gaps), which suggests that migrants selected sites with greater vertical and horizontal habitat heterogeneity. Migrating shrub-sapling-breeding species were positively associated with small-diameter stems (0–2.5 cm) and negatively associated with percentage of canopy cover (i.e. characteristics of breeding habitats). Consistently high use of mature edge-dominated and early-successional forests by a wide diversity of landbird species during fall stopover indicates the potential importance of those habitats for migratory landbird conservation.
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Vol. 121 • No. 4