Migration Monitoring Indicates Widespread Declines of American Kestrels (Falco sparverius) in North America

Abstract

We analyzed migration counts of American Kestrels (Falco sparverius) at 20 autumn migration hawkwatch sites throughout North America to estimate population trends. Prior to trend analysis, we converted counts to indexes adjusted for effort and patterns of passage. In eastern North America, autumn counts showed a pattern of significant declines along the Atlantic Coast and eastern Appalachian Mountains, stable numbers in the eastern Great Lakes region, and a significant increase in the western Great Lakes region from 1974 to 2004. From 1994 to 2004, significant declines occurred at most hawkwatch sites in eastern North America, with nonsignificant declines recorded in the western Great Lakes, northeastern Quebec, and Florida. In western North America, three counts from the Intermountain and Rocky Mountain regions that spanned the mid-1980s to 2005 showed mixed long-term trends. From 1995 to 2005, counts decreased significantly at three and nonsignificantly at two of six western hawkwatch sites active throughout the period. These results suggest population declines across much of interior western North America and the Pacific Northwest; however, kestrel counts remained comparatively stable since the mid-1980s in the southern Rocky Mountains. Migration counts along the Gulf of Mexico were variable from 1995 to 2005, with no strong indication of population changes in this region. The overall pattern of migration counts suggests that kestrel populations have undergone a long-term decline in northeastern North America and more recent declines in the midwestern and western regions of the continent.