Habitat Use And Diet Analysis Of Breeding Common Barn-Owls in Western Nebraska

I studied barn owl (Tyto alba) breeding biology in western Nebraska 1984-1986. I had greatest success capturing males (56% success) at night using trap doors at nest sites and females (91 % success) using hoop nets at nest sites during the day. Barn owls removed 16 of 23 tail-mounted radios. Eight birds were radio-tracked for 7-14.5 hours. The mean foraging range was 198 ha (32- 299 ha, n = 8) with \u3c 1 % overlap among birds from adjacent nest sites. Field-tested telemetry error was high (mean displacements of radio-locations for 2 birds were 208 and 241 m). I found no relationship between percent cover in foraging habitat and reproductive success. I identified 10,140 prey items from 15 nest sites and found both annual and seasonal variation in barn owl diets. Microtus ochrogaster occurred most frequently (32.7%) and increased in the diet from 17.6 to 27.2 to 43.5% 1984-1986. M. ochrogaster and Perognathus hispidus annual frequencies were both negatively correlated with Reithrodontomys megalotus and Peromyscus maniculatus frequencies. Prey delivery rates averaged 1.7 to 5.1 prey per hour at 4 nest sites. Males delivered 77% of the prey. Probability of a given prey species delivered to the nest was independent of the previous species delivered to the nest. Analysis of prey size and search time did not support single prey loader foraging theory. Reproductive success of bam owls appears to be influenced by nest site quality, foraging ability of parents, and diet. Advisor: Ronald M. Cas