Changes in diversity and species composition in the assemblage of live and dead bats at wind farms in a highly diverse region

Besides direct mortality, wind farms also affect aerial fauna by modifying their communities, reducing species diversity and richness through disturbance. During three consecutive years, we used mist nets and acoustic recorders, and conducted carcass searches, to characterize the assemblage of bat species and to estimate bat mortality at two nearby wind farms sited <5 km apart in a highly biodiverse region. We asked whether the diversity, richness and evenness of the assemblages varied yearly, predicting it would decrease through time. Richness and evenness did not change, but the diversity of species recorded acoustically, 96% being aerial insectivores, was significantly lower the third year. We estimate 4 - 15.7 fatalities/MW/year by wind farm, with 63% of species found as carcasses being aerial insectivores. We found >40% of dissimilarity in the species composition of bat assemblages between wind farms despite the short distance between them, with species turnover accounting for more than half of the dissimilarity every year. Similarly, species turnover accounted for >15% of the dissimilarity in the composition of the assemblage of live bats (captured and recorded acoustically) and the assemblage obtained through carcass searches. Our findings suggest that nearby wind farms impact bat communities differentially and aerial insectivores disproportionally. Long term, multi-method surveys are needed to characterize bat communities in highly diverse regions and to evaluate the post-construction effects that wind farms have on them.

Potential effect of low-rise, downcast artificial lights on nocturnally migrating land birds

Artificial light at night (ALAN) affects the flight behavior of night-migrating birds at tall or upward-pointed lighting installations. We hypothesized that common low-rise lights pointing downwards also affect the movement of nocturnal migrants. We predicted that birds in flight will react close to low-rise lights, and be attracted and grounded near light sources, with a stronger effect on juveniles during their autumn migration. We conducted a controlled longitudinal experiment with LED floodlights and considered nearby structures that turn on lights at night. We analyzed 1501 high-resolution 3D nocturnal flight paths of free-flying migrants and diurnally captured 758-2009 birds around experimental lights during spring and autumn 2016, and spring 2017. We identified change points along flight paths where birds turned horizontally or vertically, and we considered these indicatives of reactions. Flight paths with and without reactions were generally closer to our experimental site in spring than in autumn when the lights were on. Reactions were up to 40% more likely in autumn than spring depending on threshold magnitude of turning angle. Reactions in spring were up to ∼60% more likely to occur at ∼35m from the lights than at >1.5km. In autumn, some vertical reactions were ∼40% more likely ∼50m from the lights than at >2.2km. Interactions between distance to lights and visibility or cloud cover were consistent with known effects of ALAN on nocturnal migrants. Under poor visibility, reactions were up to 50% more likely farthest from structures in spring, but up to 60% more likely closest to lights in autumn. Thus, the effects of ALAN on night-migrating land birds are not limited to bright lights pointing upwards or lights on tall structures in urban areas. Diurnal capture rates of birds were not different when lights were on or off for either season. To our knowledge, this is the first study to show that low-rise lights pointing downwards affect night-migrating birds. Although the interpreted reactions constitute subtle modifications in the linearity of flight paths, we discuss future work that could verify whether the protection of nocturnal migrants with lights-out programs would have greater impact if implemented beyond urban areas and include management of low-rise lights.

Light pollution is greatest within migration passage areas for nocturnally-migrating birds around the world

Excessive or misdirected artificial light at night (ALAN) produces light pollution that influences several aspects of the biology and ecology of birds, including disruption of circadian rhythms and disorientation during flight. Many migrating birds traverse large expanses of land twice every year at night when ALAN illuminates the sky. Considering the extensive and increasing encroachment of light pollution around the world, we evaluated the association of the annual mean ALAN intensity over land within the geographic ranges of 298 nocturnally migrating bird species with five factors: phase of annual cycle, mean distance between breeding and non-breeding ranges, range size, global hemisphere of range, and IUCN category of conservation concern. Light pollution within geographic ranges was relatively greater during the migration season, for shorter-distance migrants, for species with smaller ranges, and for species in the western hemisphere. Our results suggest that migratory birds may be subject to the effects of light pollution particularly during migration, the most critical stage in their annual cycle. We hope these results will spur further research on how light pollution affects not only migrating birds, but also other highly mobile animals throughout their annual cycle.

Seasonal associations with urban light pollution for nocturnally migrating bird populations

The spatial extent and intensity of artificial light at night (ALAN) has increased worldwide through the growth of urban environments. There is evidence that nocturnally migrating birds are attracted to ALAN, and there is evidence that nocturnally migrating bird populations are more likely to occur in urban areas during migration, especially in the autumn. Here, we test if urban sources of ALAN are responsible, at least in part, for these observed urban associations. We use weekly estimates of diurnal occurrence and relative abundance for 40 nocturnally migrating bird species that breed in forested environments in North America to assess how associations with distance to urban areas and ALAN are defined across the annual cycle. Migratory bird populations presented stronger than expected associations with shorter distances to urban areas during migration, and stronger than expected association with higher levels of ALAN outside and especially within urban areas during migration. These patterns were more pronounced during autumn migration, especially within urban areas. Outside of the two migration periods, migratory bird populations presented stronger than expected associations with longer distances to urban areas, especially during the nonbreeding season, and weaker than expected associations with the highest levels of ALAN outside and especially within urban areas. These findings suggest that ALAN is associated with higher levels of diurnal abundance along the boundaries and within the interior of urban areas during migration, especially in the autumn when juveniles are undertaking their first migration journey. These findings support the conclusion that urban sources of ALAN can broadly effect migratory behavior, emphasizing the need to better understand the implications of ALAN for migratory bird populations.

Bats in a tropical wind farm: species composition and importance of the spatial attributes of vegetation cover on bat fatalities

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.

Soaring migratory birds avoid wind farm in the Isthmus of Tehuantepec, southern Mexico

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.