Bird Community Responses to Catastrophic Blowdown in the Superior National Forest

Forest composition and structure in the Upper Great Lakes is influenced primarily by disturbances such as fire and insect outbreaks, but also by infrequent, large-scale wind events. Although a number of studies of avian communities have examined the effects of disturbance in the region, few have examined the effects of wind. An unusual 1999 wind storm impacted over 200,000 hectares in northeastern Minnesota in which we had 5 permanent plots. In each, bird territories were carefully mapped and vegetation inventoried between 1997 and the storm, and through 2003 after the storm. This provided me with the nearly unique opportunity to compare pre-storm community structure with responses in the community following the storm. Analysis of variance (ANOVA) was used to test for the effect of the disturbance on vegetation structure and bird habitat usage. Principal component analysis was used to reduce the dimensionality of the vegetation data and summarize the vegetation variables followed by a canonical correspondence analysis which related differences in bird territory cover to vegetation differences between disturbed and undisturbed areas. Our data suggest that the greatest effect of the storm in terms of bird habitat was the significant decrease in tree canopy and the size of live trees as a result of the wind with a concomitant increase in shrub cover and coarse woody debris. Despite the significant changes in structure immediately following the 1999 storm, changes in bird species composition were less pronounced until two years later. From 2001 - 2003, birds preferring open habitats such as the Mourning Warbler (Oporornis philadelphia), Chestnut-sided Warbler (Dendroica pensylvanica), and Yellow-bellied Flycatcher (Empidonaxflaviventris), were more common in the blowdown. The Yellow-bellied Flycatcher, rarely recorded in the area before the blowdown, established territories in all of the blowdown areas we studied during this time period. Bird species found in mature forest, on the other hand, were generally not associated with blowdown. Blackbumian Warbler (Dendroica fusca ), Golden-crowned Kinglet (Regulus satrapa), and Bay-breasted Warbler (Dendroica castanea) were all less likely to be found in areas affected by the storm. Most notably, Bay-breasted Warbler, which was common before the blowdown, completely disappeared afterwards.United States Department of Agriculture (USDA) Forest Service, Applied Ecological Services, USDA Rural Development, and the University of Wisconsin - Stevens Point (UWSP)