¹U. S. Geological Survey, Great Lakes Science Center, Lake Superior Biological Station, 2800 Lake Shore Drive East, Ashland, Wisconsin, USA
²National Park Service, Apostle Islands National Lakeshore, Bayfield, Wisconsin, USA *Present address: U.S. Fish and Wildlife Service, Bishop Henry Whipple Federal Building,1 Federal Drive, Ft. Snelling, Minnesota, USA

Summary

         We analyzed breeding bird community structure in the Apostle Islands National Lakeshore, Wisconsin, from data collected at 106 points during 1995-1997. We also analyzed the trends in abundance during 1991-2000. Eighty-four species were identified by sight or sound, but we found that relative abundances for 9 species described most of the community structure variability. Abundance data for the 9 species showed that 3 significantly different assemblages existed in the Lakeshore. One assemblage (herein termed conifer-dominant forest) was found in a mixture of habitats, including old-growth (virgin) coniferous forest, coniferous forest, northern hardwood-hemlock (Tsuga canadensis) forest, and northern hardwood-mixed forests. A second assemblage was found mostly in northern hardwood-sugar maple (Acer saccharum) forest stands, and the third assemblage was found in pine savanna, sandscape, and shrub areas. The pine savanna-sandscape-shrub assemblage differed greatly from the other 2, and abundances of black-throated green warbler (Dendroica virens), common yellowthroat (Geothlypis trichas), red-winged blackbird (Agelaius phoeniceus), song sparrow (Melospiza melodia), yellow warbler (Dendroica petechia), ovenbird (Seirus aurocapillus), and red-eyed vireo (Vireo olivaceus) caused much of that difference. Differences in abundances of American redstart (Setophaga ruticilla), Nashville warbler (Vermivora ruficapilla), ovenbird, and red-eyed vireo caused much of the separation between the conifer-dominant forest assemblage and the northern hardwood-sugar maple assemblage. The black-and-white warbler, mourning warbler, Swainson's thrush, veery, and Nashville warbler declined during the study period in both the Apostle Islands and United States. Black-and-white warbler, Swainson’s thrush, and Nashville warbler were found in greatest abundances in the old-growth, conifer-dominant habitat. That habitat is rare in the Lake Superior basin, so we recommend conserving it to conserve black-and-white warbler, Swainson’s thrush, Nashville warbler, and other species for future generations in the Apostle Islands, Lake Superior Basin, and United States.