[Tweeters] summary: eagles and seabirds
gshugart at ups.edu
Mon Feb 25 20:36:58 PST 2008
Hi All: I had 11 responses to requests for eagle seabirds interactions. Two asked for a definition of seabirds - but any loon, grebe, cormorant, duck, gull or alcid is what I had in mind. There are many accounts of eagles eating or carrying dead birds but fewer observations of eagles taking prey. Highlights are: Eagles are often successful as pairs alternatively swooping a diving bird. Eagles might visually track a bird swimming underwater by tightly circling above it then stooping as the bird surfaces. Perhaps this is how they get coots? Diving in shallow water appears to be a bad strategy to shake a harassing eagle. There was one report from Montlake Fill of an immature eagle that harassed gull flocks for 30 min before successfully taking a gull.Single eagles on the coast appear to have specialized techniques for nabbing scoters by flying in the trough of a wave them popping over into a parallel wave to surprise prey. Other observers report taking of individual gulls and goldeneyes in the air and buffleheads, goldeneyes, scoters, grebes, pelagic cormorants and coots from the water. Montlake Fill and Woodward Bay are good places to observe eagle predation on waterbirds in the Puget Sound region.
A ww scoter appears to be the upper limit for dead lift from the water. Eagles tow ww scoters to shore by grabbing and flapping vigorously or by swimming. However, two observers positively id'd common loons that eagles carried with great difficulty up to nests.
Researchers in NE Washington report that bald eagles harass and take common loon eggs and chicks (up to 4 wk age) at loon breeding sites. Eagles have severely limited or eliminated loon reproduction at some lakes in NE Washington. All the above is not new behavior, but might be increasing in frequency with growing eagle populations. If anyone is interested I can forward a pdf of: Knight, R. L. et al. 1990. Diets of nesting Bald Eagles in western Washington, Can Field Naturalist.
The list of birds eaten is rather amazing, presumably many were found dead.
Gary Shugart, Slater Museum of Natural History, University of Puget Sound , Tacoma, WA 98416 gshugart at ups.edu,
-------------- next part --------------
An HTML attachment was scrubbed...
More information about the Tweeters