Wind energy continues to be one of the fastest growing renewable energy sources under development, and while representing a clean energy source, it is not environmentally neutral. Large numbers of bats are being killed at utilityscale wind energy facilities worldwide, raising concern about cumulative impacts of wind energy development on bat populations. We discuss our current state of knowledge on patterns of bat fatalities at wind facilities, estimates of fatalities, mitigation efforts, and policy and conservation implications. Given the magnitude and extent of fatalities of bats worldwide, the conservation implications of understanding and mitigating bat fatalities at wind energy facilities are critically important and should be proactive and based on science rather than being reactive and arbitrary.

The number of wind farms operating in the Isthmus of Tehuantepec, southern Mexico, has rapidly increased in recent years; yet, this region serves as a major migration route for various soaring birds, including Turkey Vultures (Cathartes aura) and Swainson's Hawks (Buteo swainsoni). We analyzed the flight trajectories of soaring migrant birds passing the La Venta II wind farm during the two migratory seasons of 2011, to determine whether an avoidance pattern existed or not. We recorded three polar coordinates for the flight path of migrating soaring birds that were detected using marine radar, plotted the flight trajectories and estimated the number of trajectories that intersected the polygon defined by the wind turbines of La Venta II. Finally, we estimated the actual number of intersections per kilometer and compared this value with the null distributions obtained by running 10,000 simulations of our datasets. The observed number of intersections per kilometer fell within or beyond the lower end of the null distributions in the five models proposed for the fall season and in three of the four models proposed for the spring season. Flight trajectories had a non-random distribution around La Venta II, suggesting a strong avoidance pattern during fall and a possible avoidance pattern during spring. We suggest that a nearby ridgeline plays an important role in this pattern, an issue that may be incorporated into strategies to minimize the potential negative impacts of future wind farms on soaring birds. Studies evaluating these issues in the Isthmus of Tehuantepec have not been previously published; hence this work contributes important baseline information about the movement patterns of soaring birds and its relationship to wind farms in the region.

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1. Flying birds have been documented to respond in different ways to the presence of wind farms. Such responses are species-and site-specific, with wind farm design playing an important role. Between 2009 and 2014, the length of rows of wind turbines within our study area increased from 3Á4 km to $ 7Á5 km, and the total area occupied by wind farms increased from 6Á47 km 2 to 14Á21 km 2 . This area is located on an important migratory corridor in southern Mexico. 2. We used marine radar and hawk-watch monitoring stations to collect data during six consecutive autumn seasons from a single wind farm. We analysed the response of migrating raptors to the presence of two new wind farms by comparing the mean bearing of flight trajectories and the number of intersections km À1 of trajectories with wind farm areas between 2009-2011 and 2012-2014, representing the pre-and post-construction stages of the new wind farms. 3. Mean raptor count was >600 000 individuals for the six seasons. The most abundant species were Turkey Vulture Cathartes aura, Swainson's Hawk Buteo swainsoni and Broadwinged hawk Buteo platypterus. Between 79% and 97% of migration occurred in October. Radar monitoring overlapped with the peak migratory activity each season. 4. We observed significant differences between periods, involving more scattering in flight bearings and less intersections km À1 of trajectory in the post-than in the pre-construction period, implying an avoidance of the new wind farms. 5. Synthesis and applications. We show that migrating raptors adjusted their flight trajectories to avoid new wind farms, but also discuss the extent and limitations of our findings. Our results from our hawk-watch monitoring station, which represent the first published account about the seasonality and intensity of raptor migration in the area, could be used by decision-makers for careful planning of future wind energy developments in the area. Our results might aid in the conservation of those species of raptors that migrate through the Isthmus of Tehuantepec.

Although many tropical countries have functional wind farms, most of the information on their impact on bat populations has come from temperate zones. Our study is based on a 5-year study (2009–2013) of bat captures using mist nets, acoustic recordings, and carcass searches at a wind farm in tropical southern Mexico. We investigated the composition of bat species, estimated the number of bat fatalities per turbine, and assessed the effect of the spatial attributes of vegetation cover near turbines on numbers of bat carcasses recovered by trophic guild. We recorded 29 bat species at the wind farm. The family Phyllostomidae was best represented in terms of number of species and individuals captured. Glossophaga soricina and G. morenoi exhibited the highest relative abundance, whereas Balantiopteryx plicata had the highest acoustic activity. We found 203 carcasses, including 73 Pteronotus davyi individuals (35.9%); other frequent species were Mormoops megalophylla, Molossus sinaloae, and Lasiurus intermedius. The total number of carcasses found within a year ranged from 17 to 83 (2012 and 2009, respectively), with the corrected estimates ranging from 410 to 1,980, or 4.18–20.20 fatalities/turbine. The number of carcasses recorded was positively correlated with secondary vegetation surrounding turbines but negatively correlated with agricultural fields. The spatial attributes of vegetation surrounding turbines influenced numbers of bat carcasses differentially depending on the bats’ trophic guild and habitat use. Contrary to findings from United States and Canadian wind farms, most of the carcasses observed in our study were resident species. Notably, the most commonly captured and acoustically active species were not the most commonly found in carcass searches. To obtain more accurate information about the most vulnerable species and how to reduce the impact on bat mortality, we advise the use of alternative monitoring methods in pre-construction studies. Aunque muchos países tropicales han promovido el establecimiento de parques eólicos en sus territorios, mucha de la información referente al impacto de esta actividad sobre las poblaciones de murciélagos proviene de zonas templadas. Usando datos de 5 años (2009–2013) de muestreos con redes de niebla, grabaciones acústicas, y búsquedas de cadáveres en un parque eólico al sur del trópico mexicano, investigamos la composición de especies de murciélagos, estimamos el número de cadáveres/turbina y evaluamos el efecto de los atributos espaciales de la vegetación que rodea a las turbinas sobre el número de cadáveres de murciélagos por gremio trófico. Registramos 29 especies de murciélagos en el parque, la familia Phyllostomidae fue la mejor representada en cuanto al número de especies e individuos capturados. Glossophaga soricina y G. morenoi fueron las especies con mayor abundancia relativa, mientras que Balantiopteryx plicata fue la especie con mayor actividad acústica. Se registraron 203 cadáveres de murciélagos en el parque eólico, el 35.9% pertenecían a Pteronotus davyi, otras especies frecuentes fueron Mormoops megalophylla, Molossus sinaloae y Lasiurus intermedius. El número total de cadáveres encontrado va de 17 a 83 (2012 y 2009 respectivamente), mientras que la estimación corregida va de 492–1,980, o 4.18–20.20 cadáveres/turbina. La cantidad de cadáveres estimada para los 5 años combinados es de 4,782. El área ocupada por vegetación secundaria alrededor de los aerogeneradores se relacionó significativa y positivamente con el número de cadáveres registrados. Nuestros resultados también indican que la ubicación de los aerogeneradores afecta de forma diferencial a las especies de murciélagos según sus gremios tróficos y uso de hábitat. Contrario a lo encontrado en parques eólicos de Estados Unidos y Canadá, los cadáveres de murciélagos registrados en el parque eólico tropical son de especies residentes, incluyendo aquellas que forman grandes colonias. Ya que algunas de las especies frecuentemente registradas en las redes y acústicamente, no fueron las que se encontraron frecuentemente en los cadáveres, sugerimos diversificar los métodos de monitoreo en estudios de pre-construcción para identificar las especies más vulnerables y tomar acciones que reduzcan el impacto sobre sus poblaciones.