Community structure and trends in abundance of breeding birds in the Apostle Islands National Lakeshore, Wisconsin

Hoff, Michael; Van Stappen, Julie

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 and 1996-2000. Eighty-four species were identified by sight or sound, but we found that relative abundances for 9 species described most of the internal variability of the data for all species. 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 of the conifer-dominant forest assemblage from that in 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.