What migrating Sharpies eat
Feathers plucked from Sharp-shinned Hawks’ beaks and talons reveal an unexpected taste for larger-than-expected birds
Published: February 15, 2013
The standard way to determine what a bird of prey eats is to examine what’s left behind after its meals. The method works well during the breeding season, but it’s of no use after the birds move on.
Photo by U.S. Fish and Wildlife Service
What do raptors eat while migrating? Biologists who captured 72 Sharp-shinned Hawks at a hawk watch in the Manzano Mountains in New Mexico recently took a novel approach to answering that question.
They checked the hawks’ beaks and talons for prey species’ feathers, which the scientists gathered. Then, back in the lab, they extracted nucleotide sequences from the feathers and compared them to genes obtained from reference feathers taken from 57 bird species netted at banding sites located not far from the hawk watch.
The results showed that migrating Sharpies take most of their prey in proportion to its abundance. Twenty species were identified conclusively, including three species never before described as Sharp-shinned Hawk prey: Ladder-backed Woodpecker, Bullock’s Oriole, and Townsend’s Warbler.
The most common prey species were American Robin and Hermit Thrush. Both are larger than most potential prey, and the hawks took both more frequently than expected.
Why Sharpies show an inclination to feed upon relatively uncommon and large prey isn’t clear, write the researchers, “but selecting larger prey would be consistent with an optimal foraging strategy whereby hawks maximize energy intake per hunting attempt or hunting time.”