Date of Award
Bachelor of Arts
Joan L. Morrison
Craig W. Schneider
Michael A. O'Donnell
I tested whether or not raptors on the east coast are shifting the timing of their autumn migration. I analyzed 38 years of passage data at three count sites across New England: Hawk Mountain, Quaker Ridge, and Lighthouse Point. I studied four raptors with diverse natural history traits: Red-tailed Hawk (Buteo jamaicensis), Northern Harrier (Circus cyaneus), Sharp-shinned Hawk (Accipiter striatus), and Broad-winged Hawk (Buteo platypterus). I also investigated possible factors associated with any documented shift, including climate, distance of migration, diet, and population trend. Long-distance migrants should advance their migration and short-distance migrants should delay their migration, as reported for numerous taxa, including raptors, in Europe. Raptors that feed primarily on birds should advance their migration. Species advancing their migration should advance it further in warm years, while species delaying their migration should delay it further in warm years. Finally, I predicted that species in decline would show little or no shift in migration timing; species unable to adjust to climate change may be at a disadvantage. The Red-tailed Hawk and Northern Harrier delayed their autumn migrations past these three count sites, while the Sharp-shinned Hawk advanced and the Broad-winged Hawk showed no shift in its migration phenology. Some of these results match my predictions based on the raptors' life history traits, but some do not, suggesting that North American raptors are responding to climate change differently from European raptors. The Broad-winged Hawk is the only raptor among the four species I studied that is not shifting and it is currently declining in population in the Northeast. This species may be more "hard-wired" to migrate at roughly the same time every year, and that inability to shift may be contributing to population decline.
Baird, Jason M., "Raptors on the East Coast: A Shift in the Timing of Autumn Migration". Senior Theses, Trinity College, Hartford, CT 2014.
Trinity College Digital Repository, https://digitalrepository.trincoll.edu/theses/422