Until now, it was unclear whether all age groups or sexes were equally at risk.
A comparison of the age, sex, and origin of Nathusius' pipistrelle bats killed at wind turbines with living members of the same species near the installations now shows that juvenile animals die at wind turbines at a disproportionately high rate. Females are struck by wind turbines more frequently than males — though this reflects their higher proportion in local populations. The high number of juveniles and females killed could have long-term negative effects on population development. The current practice of wind energy generation therefore appears to be ecologically unsustainable. The study was led by scientists at the Leibniz Institute for Zoo and Wildlife Research (Leibniz-IZW) and has been published in the journal «Ecological Applications».
In efforts to reduce the negative impact of greenhouse gas emissions on the global climate, many countries are promoting energy generation from renewable sources such as wind power. Although wind energy is considered environmentally friendly, it comes with considerable costs to biodiversity. On the one hand, animal populations suffer habitat loss when wind turbines are constructed in sensitive areas such as forests or wetlands. On the other hand, birds and bats can be killed by the operation of wind turbines — either through direct collision with the rotating blades, or — in the case of bats — also through a so-called barotrauma caused by the air turbulence at the rotor blades. Until now, it was unclear whether certain age groups or sexes of bats are particularly at risk from wind turbines. A higher vulnerability of, for example, female or young bats could have significant consequences for local populations.
"In the course of our study, we found more young Nathusius' pipistrelle bats (Pipistrellus nathusii) dead beneath wind turbines than would have been expected based on their proportion in local populations. This suggests that young bats are particularly at risk from wind turbines," says Dr. Christian Voigt, head of the Leibniz-IZW Department of Evolutionary Ecology and lead author of the study. "We found this disproportionately high share of young bats among turbine fatalities at low wind turbine densities in areas with bodies of water and forests — that is, in regions where Nathusius' pipistrelles breed. In areas with a high density of wind turbines, such as coastal regions, age groups and sexes died at rates corresponding to their relative occurrence in the living population." A high mortality rate among young Nathusius' pipistrelles at wind turbines can throw the natural age pyramid out of balance. Voigt and his team also regard the frequent death of female animals as a problem for the conservation of migratory bats. "Females and juveniles are extremely important for ensuring the long-term viability of colonies. Protecting bats at wind turbines should therefore be a primary objective in the planning and operation of wind energy facilities," says Voigt.
Voigt and his colleagues examined the characteristics of approximately 650 nathusius' pipistrelles during the summer migration period in Germany. They analyzed sex, age, and geographic origin — both of bats that had been killed (119) and of individuals from local populations (524) caught in nets or observed in artificial roost sites. To distinguish bats from local populations from those that had migrated from the Baltic-Russian region, they analyzed stable hydrogen isotopes in the animals' fur. "In contrast to sex and age, however, the origin of a bat had no influence on the probability of being killed at a wind turbine," says lead author Cecília Kruszynski de Assis, a doctoral researcher in the Department of Evolutionary Ecology at the Leibniz-IZW. "Our study does show, however, that wind turbines can have unequal impacts on different subgroups of migratory bats. Measures to prevent high collision rates/fatalities at wind turbines, such as seasonal shutdown periods during the night and in weather conditions favorable to bats, should be implemented across Europe to prevent a decline in populations of migratory bats such as the nathusius' pipistrelle.»
