Breeding Dispersal By Burrowing Owls (Athene cunicularia) In Idaho

Abstract

Breeding dispersal, the movement between successive breeding sites, is important to many aspects of life history and population dynamics but poorly understood for many raptor populations. We used longitudinal data collected from Burrowing Owls (Athene cunicularia) nesting in southwestern Idaho from 1994–2007 to examine characteristics of breeding dispersal behavior. First, we measured frequency and distance of breeding dispersal and compared those to published results from other owl populations. The dispersal frequency (78%, n = 86) was greater than previously reported for any Burrowing Owl population and for most owl species. The mean distance dispersed (835 ± 98 m [SE]) was slightly greater than reported distances for most other Burrowing Owl populations. Second, we examined factors associated with two decisions owls faced between breeding seasons: whether to move to a new nest site (dispersal likelihood), and how far to move if dispersing to a new site (dispersal distance). We assessed the potential effects of sex, productivity, age, and site quality on breeding dispersal likelihood and distance. Owls were more likely to disperse if they were female and if they had fledged fewer young in the previous breeding season. Nesting failure was a perfect predictor of breeding dispersal, but high productivity did not always result in philopatry. Owls dispersed farther if they were relatively younger, female, had lower productivity in the previous breeding season, and had previously nested in lower quality sites. Our comparisons to other studies indicate that the factors that most influence breeding dispersal behavior in Burrowing Owls appear to vary among populations and may relate to migration tendency and geographic heterogeneity.