Camera-Trapping Versus Conventional Methodology in the Assessment of Carcass Persistence for Fatality Estimation at Wind Farms

Abstract

In the last decades, there has been a worldwide increase in wind energy. Despite its advantages, wind farms carry negative impacts on bird and bat populations, such as direct mortality due to collision with wind turbines. Carcass searches beneath the turbines are mandatory to access this impact, as well as the assessment of two correction factors: searcher efficiency and probability of carcass persistence. The latter considers the possibility of carcass removal by scavengers (or any other event such as decomposition) between monitoring sessions, influencing the number of carcasses detected. Carcass persistence trials consist in randomly placing carcasses under the turbines and, in this study, checking them daily during a 15-day period. Camera traps are looked as an alternative that might reduce human and financial effort while allowing the collection of the exact removal time and characterization of the scavenger’s guild. We conducted trials in three different wind farms, in a total of seven campaigns (15-day carcass checking periods), across different seasons. We compared the camera-trapping with the conventional methods and analyzed the influence of using continuous vs. censored data on the correction factor estimate and have not found significant differences. Camera traps allowed the recording of the exact removal time and the identification of the removal agent for most of the carcasses and allowed a significant reduction of the field work and the costs associated. We present a few guidelines to be taken into consideration when using this method. Camera-trapping demonstrated to be a good method to replace the conventional method, ensuring at least the same results, while allowing the characterization of the scavenger’s guild and a significant cost reduction.