Factors affecting searcher efficiency and scavenger removal of bat carcasses in Neotropical wind facilities

Abstract

Bat fatalities at wind facilities have been reported worldwide, and environmental impact assessments depend on searches for carcasses around wind turbines to quantify impacts. Some of the carcasses may go undetected by search teams or be removed by scavengers during search intervals, so these biases must be evaluated and taken into account in fatality estimation. We investigated the influence of different factors on searcher efficiency and scavenger removal in a dry forest area in northeastern Brazil, one of the regions with the highest density of wind turbines in the Neotropics. We conducted searcher efficiency and scavenger removal trials around 34 wind turbines from January 2017 to January 2018. Searcher efficiency was influenced by cover type, season, and carcass size, ranging between 12% for small bats in shrub vegetation during the rainy season and 96% for large bats in absent or sparse vegetation during the dry season. Carcass type and season affected scavenger removal; carcass persistence time was shorter for chicks (1.2 days) than for bats and mice (2.1 days), and the probability of a carcass persisting for a whole day was higher in the rainy season, while the probability of carcass persistence for 7, 14, and 28 days was higher in the dry season. The scavenger community was composed of canids, birds of prey, and insects, with systematic removal of carcasses by the crab‐eating fox (Cerdocyon thous) throughout the year and by dung beetles in the rainy season. Based on our findings, impact assessments of wind facilities on bats should conduct searcher efficiency trials in all seasons and cover types around wind turbines, using bat carcasses or models of different sizes. Scavenger removal trials should cover all seasons as well, and use mouse carcasses (but not chick carcasses) as surrogates for bats.

Wind turbines without curtailment produce large numbers of bat fatalities throughout their lifetime: A call against ignorance and neglect

“…We estimated searcher efficiency with fresh brown mice carcasses (Myodes glareolus, Cricetidae, Rodentia), obtained from a seminatural population at a facility where they were maintained under veterinarian control. We considered mice carcasses as suitable surrogates of bat carcasses because previous studies in Europe showed that the persistence time and detection probability of carcasses is similar in these taxa (Niermann et al, 2011;Barros et al, 2022). At each of the turbines, one of us placed 10 mice carcasses in a random design.…”

“…For example, Rydell et al (2010) reported that 1.3 (median; range 0-41) carcasses were documented per wind turbine and year in Central Europe (Germany, Switzerland, and Austria). But Many carcasses are not found by searchers because the small size of animals impairs the detection probability (Niermann et al, 2011;Barros et al, 2022), particularly when the search area consists of a heterogeneous surface or when vegetation is high. Also, some of the carcasses may have been consumed or carried away by scavengers, such as foxes and crows.…”