NONBREEDING SEASON DIET OF NORTHERN SAW-WHET OWLS, AEGOLIUS-ACADICUS, ON NANTUCKET ISLAND, MASSACHUSETTS

Diet of Northern Saw-whet Owls was studied from 1985 to 1988 on Nantucket Island, Massachusetts. Eight owls were observed over a four-year period. Two hundred twenty-five prey items were recorded from 448 pellets. Two species of rodents and three species of insectivores accounted for all identified prey. White-footed Mice were dominant prey by number in three of four years, and biomass in two years. In 1987, Meadow Voles were dominant prey by number and biomass. Juveniles accounted for 56.9% of the voles eaten during the study. Based on estimated prey biomass, 74% of the prey items identified ranged between 18 and 22 grams. Food niche breadth and dietary evenness ranged from 1.31 to 2.44 and 0.430 to 0.832, respectively. Based upon skull frequencies, prey per pellet was 0.50. Mean pellet dimensions for length and width were, 29.3 x 15.5 mm.