Date of Final Oral Examination (Defense)
Type of Culminating Activity
Master of Science in Raptor Biology
Julie A. Heath, Ph.D.
Jesse Barber, Ph.D.
Karen Steenhof, M.S.
With rapid increases in outdoor recreation, and mounting evidence of impacts to wildlife, public land managers and biologists need better information on the nature of this potential disturbance. Outdoor recreation may impact wildlife negatively via human disturbance or habitat degradation. Golden eagles (Aquila chrysaetos) in shrub-steppe habitats face several current and emerging threats, including increased non-motorized and motorized (off-highway vehicle, OHV) recreation. We tested the hypothesis that recreation affects eagle breeding biology by monitoring eagle behavior and reproduction in response to recreation volume and activity types, and landscape features associated with recreation. We also investigated the probability that an adult golden eagle would flush, examined flight initiation distance (FID), and documented total time off the nest following flushing events in response to motorized and non-motorized recreationists.
Territories with higher seasonal-average OHV volumes were less likely to be occupied than territories with lower seasonal-average OHV volumes, despite uniformly low OHV volume across all territories during the pre-breeding period. For non-migratory species, like eagles in southern Idaho, decreased occupancy during the breeding season may be the result of carry-over effects of disturbance in the non-breeding season, degraded habitat, or both. At occupied territories, early season volumes of pedestrians and other non-motorized recreationists negatively influenced adult eagle nest attendance and the likelihood of egg-laying. Behavioral observations of breeding birds revealed that adult nest attendance, a strong predictor of success, was associated negatively with the volume of pedestrians, and most pedestrians observed near the nests reached the area via motorized vehicles. In addition, nest survival was affected negatively by interval-specific OHV volume recorded by trail cameras.
In most (87.1%, n = 279) instances, adult eagles did not respond to recreationists passing within 1200 m. Flushing was more likely to occur if eagles were perched away from the nest than if eagles were at the nest. FID was greater in the earlier portion of the breeding season, suggesting seasonal changes in the costs and benefits of responding to disturbance. Type of recreation activity did not affect the probability of flushing or FID, but flushing occurred frequently (36%, n = 36) when motorized recreationists stopped and changed their behavior near eagles. Recreationists on foot frequently go off trail and follow less predictable movement patterns than motorized recreationists and might create greater perceived risk.
Taken together, these results suggest that OHVs may facilitate disturbance events leading to nest failure by transporting motorized recreationists, who become pedestrians, to areas near eagle nests. We propose that landscape features suitable for eagle nesting, like steep canyons and rocky outcrops, also inspire recreationists to transition from predictable movements along a trail to less predictable stop-and-go hiking; less predictable recreation activities may increase perceived risk for eagles. Expanding existing trail management efforts to consider the effects of pedestrian and non-motorized recreation, especially during the early portion of the breeding season, could help improve eagle productivity. Limiting motorized and non-motorized recreation activities within 650 m and 1000 m of nest sites may decrease flushing events by 77% and 100%, respectively. Trail management efforts on public lands may strike a balance between the needs of recreationists and eagles by implementing “no-stopping” zones near known eagle nesting areas.
Spaul, Robert J., "Recreation Disturbance to a Shrub-Steppe Raptor: Biological Consequences, Behavioral Mechanisms, and Management Implications" (2015). Boise State University Theses and Dissertations. 995.