Effects of Old Nest Material on Occupancy and Reuse of Artificial Burrows, and Breeding Dispersal by Burrowing Owls (\u3cem\u3eAthene Cunicularia\u3c/em\u3e) in Southwestern Idaho

This thesis comprises two chapters describing my investigations of the breeding ecology of burrowing owls (Athene cunicularia) in southwestern Idaho. The first chapter details two experimental studies where I examined the effects of old nest material, primarily mammal dung, on the occupancy and reuse of artificial burrows by burrowing owls in 2004 and 2005. For burrows that owls had not used previously for nesting, adding material from actual nests did not induce occupancy. Thus, old nest material does not appear to function as a cue for burrow suitability. Removing old material from burrows that owls had used for nesting in the previous year caused a decrease in reuse rates, but it had no effect on the level of ectoparasitism or reproductive performance (e.g., number of young fledged or body condition of owlets). While the presence of old material does not seem to increase the owls‟ fitness, it may help owls locate specific burrows (for which they have public information) when returning from migration. The second chapter consists of an observational study, where I used data collected during a long-term study of burrowing owls (1994-2007) to address questions about breeding dispersal, or the movement between breeding sites. I examined the percent frequency of owls dispersing and the distance they dispersed, and I compared those to published results from other burrowing owl populations. Additionally, I assessed the effects of sex, productivity, age, mate quality, site quality (as measured by four indices), and level of ectoparasitism on breeding dispersal likelihood and distance. The percentage of owls dispersing (78%; 67 of 86) was greater than previously reported for any owl species. The mean distance owls moved (834.6 m ± 98) was slightly greater than reported distances for most other burrowing owl populations. With the exception of mate quality and two site quality metrics (burrow productivity and proportional occupation), all factors had support for an important relationship with dispersal likelihood. Owls were more likely to disperse if they failed to fledge young, were female, were young, nested farther from agriculture, had closer nesting neighbors, and had lower levels of ectoparasitism. Ectoparasitism and distance to nearest neighbor had inverse rather than the expected direct relationships. Age and one index of site quality were the only predictors with strong relationships to dispersal distance; young owls and owls nesting farther from other owls dispersed longer distances. Sex was somewhat important to distance dispersed, with females moving farther. The factors that most influence breeding dispersal behavior in burrowing owls appear to vary among populations