Food Habits of the Endemic Ashy-Faced Owl (Tyto glaucops) and Recently Arrived Barn Owl (T. alba) in Hispaniola

Abstract

The Ashy-faced Owl (Tyto glaucops) is endemic to Hispaniola, where the Barn Owl (T. alba) became established after ca. 1950. I examined 8322 vertebrate prey of the two species, using regurgitated pellets and prey remains from 12 localities in five habitats in the Dominican Republic to determine diets and feeding-niche characteristics of the owls. Owl diets differed among prey classes in frequency and biomass. Mammals, mainly introduced rodents, predominated in the diets of Ashy-faced Owls (52.0% frequency, 73.9% biomass) and Barn Owls (76.7% frequency, 90.7% biomass), with bats forming a substantial proportion for both species (Ashy-faced Owl: 11.1% frequency, 2.6% mass; Barn Owl: 12.2% frequency, 2.2% mass). Birds made up a greater proportion of Ashy-faced Owl prey (28.8% frequency, 14.8% mass) than of Barn Owl prey (12.3% frequency, 5.1% mass). Reptiles and amphibians were unequally represented in Ashy-faced (19.2% frequency, 11.3% mass) and Barn (11.1% frequency, 4.3% mass) owl diets. Niche overlap was moderate overall (α = 0.60). Ashy-faced Owl prey materials contained 125 vertebrate species, whereas Barn Owl materials included 114 species, with 92 species in common between the two owls. The Ashy-faced Owl had a more diverse prey base (H′ = 3.04, D = 6.32, J = 0.610) than did the Barn Owl (H′ = 2.21, D = 2.93, J = 0.444). I could not determine whether niche overlap resulted in competition between the two owl species.