Brown-Headed Cowbird Response To Kirtland's Warbler Habitat Management
Lauren A. Bailey, Michigan State University, 13 Natural Resources Building, East Lansing, MI 48824; (517) 353-5135; FAX (517) 432-1699; bailey65@msu.edu
Kelly F. Millenbah, Michigan State University, 13 Natural Resources Building, East Lansing, MI 48824
In 1965, the U. S. Fish and Wildlife Service, U. S. Forest Service, and Michigan Department of Natural Resources initiated a collaborative effort to create and maintain viable habitat for the endangered Kirtland's warbler (Dendroica kirtlandii). The current management plan includes clearcuts and replantings of jack pine on a 50-year rotation. While warblers require large (>81 ha) tracts of even-aged jack pine for optimal breeding success, smaller stands (2-80 ha) continue to be managed for the species. Little information currently exists on the impacts of this habitat management on brown-headed cowbird (Molothrus ater) abundance, a species that effectively parasitizes warbler nests. The purpose of this study was to determine if a correlation exists between jack pine stand size and age and cowbird abundance. Because cowbirds respond positively to fragmented landscapes, we hypothesized that they would be proportionately more abundant in smaller stands than large. We also predicted that cowbirds would be more abundant in young, open clearcuts rather than dense, older jack pine stands. Avian point-count censuses and vegetation sampling were performed May-July 2004 in Clear Lake State Park in northern Lower Michigan. This site was actively managed for warbler habitat, but was not in the range of the cowbird removal program. Twenty-six large and small stands were censused in three age categories: 0-5, 6-20, and >20 years. Preliminary results suggest that relative cowbird abundance is greater in small stands, but the effects of stand age are inconclusive. Smaller stands that support more cowbirds may inadvertently increase cowbird numbers in larger stands generally occupied by Kirtland's warblers especially if these different sized stands occur in relatively close proximity to one another.