Predation on seabirds by sea otters

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Abstract
Although rarely reported in the past, predation by sea otters (Enhydra lutris) on seabirds has been observed more frequently in the last decade. A total of 23 incidents of definite or probable predation on seabirds have been observed in California (20) and in Alaska at Amchitka Island (3). In California, the most commonly eaten species were western grebes, although cormorants, gulls, common loons, and surf scoters were also consumed. All cases of seabird predation in California have occurred in the northern part of the sea otter's range in three locations: Point Lobos, Stillwater Cove, and the Monterey harbor area. When sex could be determined, most of the otters observed feeding on seabirds were adult males. At one site, it appeared that the same individual repeatedly captured birds. Predation on seabirds is indicative of the sea otter's ability to learn new and innovative foraging tactics, and is consistent with a high degree of individual variation in diet observed among sea otters in Monterey. Sea otters initially capture birds by diving and grabbing them from underwater while the bird rests on the surface, in a manner similar to that employed by coastal river otters to capture seabirds. When mink, freshwater-inhabiting otters, and sea otters are compared, a graded reduction in the tendency to eat birds appears to occur in the more aquatic mustelids, with the relative importance of birds in the diet being greatest in mink and least in sea otters.

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