Modeling the Effect of Roadkill Carcass Removal on Eagle Mortality

Mitigation actions to compensate for mortality of protected species succeed when three critical capacities are achieved. Successful ‘offsetting’ must be (1) equivalent – the biological gains qualify as acceptable... [ view full abstract ]

Mitigation actions to compensate for mortality of protected species succeed when three critical capacities are achieved. Successful ‘offsetting’ must be (1) equivalent – the biological gains qualify as acceptable replacements for lost organisms; (2) sufficient – the quantity of replacements will offset specific losses, including buffers to hedge against possible short-falls due to uncertainty; and (3) efficient - the tactical strategies produce the greatest degree of direct compensation per increment of investment in the mitigation program. We illustrate with a case study on abating vehicle collisions with golden eagles in the western United States. Our model estimates eagle scavenging, avoidance, and vehicle collision rates as a function of eagle densities, roads and traffic volumes, and animal carcass abundance at the scale of a rural Wyoming county during fall-winter. The prototype model indicates collision abatement could reduce eagle deaths by 1-5 per winter at a ‘cost’ of 12,000-34,800 km driven per eagle saved, depending on the removal strategy. Removal efficiency (eagles saved/km) was tied to average carcass persistence times and concentrated on lower traffic volume roads where fewer eagles avoid scavenging yet routine road maintenance is infrequent. Collision abatement is a potentially useful addition to the mitigation toolbox where wind energy development is constrained by potential predicted eagle mortality. Simulation modeling and scenarios provided a rigorous yet practical approach to analyzing the sufficiency and efficiency of compensatory offsets, and identifying the best available mitigation and research strategies.