TROPHIC NICHE OF NEARCTIC SHORT-EARED OWLS

The trophic niche of Short-eared Owls (Asio flammeus) was analyzed using nine Nearctic studies reporting > 500 prey items each. Of 20,416 prey items, 4136 were from the breeding and 16,280 from the non-breeding seasons. The owls preyed upon at least 62 species from four classes of animals. Mammals constituted > 95% of prey from all but two sites. Food-niche breadth ranged from 1.23 to 5.20 (xBAR = 1.87), for combined studies, 1.31 to 1.87 (xBAR = 1.50) for breeding, and 1.23 to 5.20 (xBAR = 2.00) for non-breeding seasons. Dietary evenness values ranged from 0.315 to 0.703 (xBAR = 0.435), for combined studies, 0.331 to 0.404 (xBAR = 0.365) for the breeding season, and 0.315 to 0.703 (xBAR = 0.458) for the non-breeding season. Estimated prey masses ranged between 28 and 325 g. Most prey, however, weighed between 28 and 100 g. Short-eared Owls from coastal areas preyed more on birds than those at inland sites.