Dietary Overlap of American Barn Owl and Short-Eared Owl in the Mission Valley, Montana

Abstract

The Mission Valley is home to many species of wildlife, including the Short-eared owl.  Over the last decade Barn Owl sightings have increased in the valley and nests have been discovered.  We analyzed food-niche overlap between American Barn Owls (Tyto furnata) and Short-eared Owls (Asio flammeus) over one year to determine whether prey competition from the local Barn Owl population will affect the Short-eared Owl population. A total of 325 prey items (11 different species) were identified from 152 pellets; 79 Barn Owl and 73 Short-eared Owl.  Diets of both species consisted primarily of Microtus species, although traces of additional food resources were present. Using Pianka’s index the food-niche overlap was 0.658, where Pianka’s index determines what proportion of the two owl species’ diets overlap with a value of 0 representing total separation and a value of 1 representing total overlap.  The results of this study showed a food niche overlap between the two owl species. We suggest, however, that the current population of Barn Owl in the Mission Valley is not directly competing with the established Short-eared Owl population in the Mission Valley, given the