Brown-headed cowbird response to Kirtland's warbler habitat management and cowbird trapping in Michigan.

摘要

Brown-headed cowbirds (Molothrus ater) have been of concern to wildlife managers due to the often negative effects of their parasitic breeding practices on avian communities. In Michigan, the cowbird host species most impacted is the endangered Kirtland's warbler (Dendroica kirtlandii ), whose breeding grounds comprise middle-aged (6-20 years) jack pine forests. The Kirtland's warbler recovery plan includes extensive jack pine restoration and intensive cowbird trapping. The overall goals of this project were: (1) to analyze the effects of jack pine stand sizes and ages on cowbird relative abundance and density, (2) to determine correlations between cowbird trap captures and surrounding land cover, and (3) to develop a habitat suitability index model for the brown-headed cowbird. Avian point counts and vegetation surveys were performed to collect data on cowbirds in Kirtland's warbler habitat. Cowbird abundance was greater in large stands (> 81 ha), had no association to stand age, and was positively correlated with host abundance and species richness. To answer question 2, Michigan land cover data were analyzed with cowbird trap data in ArcView GIS. Cowbird captures were positively correlated with agricultural and urban areas, and with upland deciduous and mixed forests, and were negatively correlated with upland and lowland coniferous forest. Finally, I constructed a habitat suitability index (HSI) model for the brown-headed cowbird using the following suitability index variables: distance to feeding areas, distance to edge, percent ground cover and percent mid-story cover.