Migration of Woodland Birds at a Fragmented Inland Stopover Site

The abundance, timing, and habitat distribution of woodland-associated migrants were examined at a migratory stopover site in the St. Croix River Valley, Washington County, Minnesota during spring and autumn migrations, 1984-1986. Five wooded habitats (1-3+ ha) were studied using mist nets. Migrants made up 92% of the species (N = 100) and 94.8% of the individuals (N = 17,019) captured. Of the 69 most common migrant species, 58 (84%) were Nearctic-Neotropic migrants. Analyses of median passage dates suggest that peak numbers, and thus resource demands, occurred in the days surrounding 14 May and 31 August. Eighteen migrant species (53% of those adequately covered by our study periods) showed a difference between median spring and autumn passage of 105 days or less, and thus spend less than 30% of their annual life cycles on their breeding grounds. Seasonal absences or higher capture rates in spring suggest that seven species in our region use migratory routes differing from the regional norm. The distributions of birds at our site changed between seasons, suggesting a spatial shift in habitat use by the entire avian community.