TRAILS Model: Tolerance in Raptors and the Associated Impacts of Leisure Sports

There is widespread evidence that human disturbance affects wildlife behavior, but long-term population effects can be difficult to quantify. Individual-based models (IBMs) offer a way to assess population-level, aggregate effects of disturbance on wildlife. We created Tolerance in Raptors and the Associated Impacts of Leisure Sports (TRAILS), an IBM that simulates interactions between recreationists and nesting raptors, to assess the effect of human disturbance on raptor populations and test if changes in tolerance to disturbance could mitigate negative consequences. We used behavioral and demographic data from golden eagles Aquila chrysaetos, and recreation activity data to parameterize TRAILS and simulate the effects of pedestrian and off-highway vehicle (OHV) recreation on the likelihood of territory occupancy, egg-laying and nest survival of eagles over 100 years. We modeled eagle populations in the absence of recreation, with stationary 2014 levels of recreation, and with annual increases in recreation. Furthermore, we simulated eagles that developed tolerance to disturbance randomly, through natural selection, habitat imprinting, or habituation. In the presence of recreation, simulated eagle populations had significantly lower and more variable growth rates, population sizes and territory occupancy. Annual increases in recreation of 1–2% greatly exacerbated population declines. Though both habituation and natural selection lead to more tolerant eagle populations, neither buffered eagle populations from detrimental effects of recreation. These results suggest that long-lived species that experience encroachment from human activities may not adapt to human disturbance at a rate that compensates for changes in disturbance. This project illustrates the usefulness of IBMs for evaluating non-lethal threats, forecasting population changes and testing theoretical feedbacks in system processes