Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Raptor Biology
James R. Belthoff, Ph.D.
T. Trevor Caughlin, Ph.D.
Christopher J. W. McClure, Ph.D.
Barn Owls (Tyto alba) are a species of conservation concern in many portions of their cosmopolitan range. One important factor contributing to population declines and sometimes local extirpations is roads, which can cause direct mortality through Barn Owl-vehicle collisions, fragment habitat, limit dispersal and movement, and imperil long-term population viability. However, the effects of roads on Barn Owl reproduction are less clear. Further, the cumulative effects of roads on Barn Owls can be dependent on how they respond to them. Road and traffic responses of animals have been classified into four categories: 1) speeders, who increase speed to cross roads, 2) pausers, who pause before crossing, 3) avoiders, who avoid crossing roads altogether, and 4) nonresponders, who have no response to roads or traffic. Barn Owls, who are frequent victims of road mortality around the world and may even be attracted to the areas along roads for foraging, are hypothesized to be nonresponders. My goals were to examine Barn Owl behavior near roads to assess the extent to which they exhibited traits of nonresponders as well as to assess the possibility that they were attracted to areas near roads. Additionally, I aimed to examine the potential effects of roads on Barn Owl reproduction.
To help understand Barn Owl behavior near roads I attached and recovered GPS data loggers from 19 Barn Owls to obtain location data on their movements. I first conducted a random walk analysis to assess how Barn Owl crossing rates and proximity to roads compared to what would be expected by chance. Additionally, I analyzed individual road encounters to help understand how flight dynamics affected their decision to cross a road and their behavior when actually crossing. I found that owls crossed fewer roads than expected, especially highways and interstates. Additionally, Barn Owls did not fly closer to roads than expected, including major roads and those of any size. When encountering roads, Barn Owls were more likely to cross when they approached at higher altitudes and when roads were narrower in width. When crossing roads, Barn Owls accelerated to cross when approaching at higher altitudes and slower speeds. They also decreased crossing altitude when approaching at higher altitudes and increased altitude to cross wider roads. These findings suggest that rather than being strict nonresponders, Barn Owls showed evidence of traits more associated with speeders and avoiders.
To assess the potential effect of roads on Barn Owl reproduction I monitored a nest box population of Barn Owls between 2019 and 2022 to record breeding occupancy and productivity (number of fledglings) during two breeding seasons (2020 and 2021). I assessed occupancy in an average of 276 nest boxes per year and found that occupancy was 66%. Nests produced an average of 3.7 fledglings across the two breeding seasons (n = 225 nests). Both breeding occupancy and productivity decreased with proximity to roads. These results suggest that roads have the potential to influence owl populations not only through wildlife-vehicle collisions but indirectly through reductions in occupancy and productivity. Although it is alarming that roads are further impacting Barn Owls through their reproduction, my behavioral research suggests that rather than being strict nonresponders to roads, Barn Owls may avoid them to some degree, as well as reduce their risk of collision when crossing through changes in speed and altitude. Given the continuing expansion of road networks across the globe and the negative effects of roads on Barn Owl reproduction, it is encouraging that Barn Owls may be preadapted to the threat of roads, if not currently evolving adaptations in light of selective pressure, providing hope for the conservation of this species in a new and changing environment.
Busby, Brian Thomas, "The Effects of Roads on Movement, Flight Dynamics, Occupancy, and Productivity in Barn Owls (Tyto alba)" (2022). Boise State University Theses and Dissertations. 1920.