Abstract
Large soaring raptors vs wind turbines development in the Swiss Alps is an applied research project launched by the Division of Conservation Biology, University of Bern, in autumn 2014. The project’s main objectives were to develop spatially-explicit models that may assist governmental agencies and non-governmental associations in their decision-making process regarding the suitability of foreseen locations for the installation of wind turbines from the viewpoint of the conservation of raptors, which are key elements of Alpine biodiversity. The idea is to avoid as much as possible potential airspace conflicts between large soaring raptors and future wind energy development. A recent Europe-wide study ranked Switzerland among the countries with the lowest per capita wind energy production (Iten & Nipkow, 2019) but the Swiss government has planned to boost this industry, via massive subsidies, with the objective to reach a wind electricity production of 4,3 TWh by 2050 (Bundesamt für Raumentwicklung ARE, 2020), compared to a present day production of around 0.14 TWh. Numerous new wind turbine projects are thus expected in the coming years but their deployment, in particular in fragile high-altitude ecosystems harbouring emblematic biodiversity, might impact not only valuable habitat but could also increase the mortality of Alpine birds and bats colliding with the rotor blades. Our research focuses on two of the principal large resident raptor species in the Swiss Alps, namely the bearded vulture (Gypaetus barbatus) and the golden eagle (Aquila chrysaetos). These two species are at particular risk of collision with the wind turbine blades due to their large home ranges and extensive daily movements. Moreover, their late sexual maturity and low breeding rate render them particularly vulnerable from a population dynamic viewpoint. As demonstrated by Schaub et al. (2009), a slight increase in annual mortality rate of only 60% would lower the survival rate of bearded vultures to a degree that would threaten the reintroduced Alpine population with extinction in the mid and long term. A re-actualisation of the model (Schaub et al., in prep.) with more recent data showed a similar pattern. The current Alpine population of the bearded vulture numbers in the 300 individuals and faces an average annual survival rate of 95%. This means that this population currently loses 15 individuals per year. An increase by 60% of the present day mortality would mean that nine additional losses per year would put the population at extinction 5 risk. In other words, if all the wind turbines installed in the entire Alpine massif would kill nine bearded vultures a year, the population would be doomed in the long run as it would start to progressively decline to extinction.
Hazardous airspace conflicts are expected to occur if wind energy facilities are constructed in topographic situations frequently overflown by the birds. The deliverables of this study are predictive maps of raptors’ space use that rank Alpine geographic areas according to the probability of occurrence of these two species of raptors. In the following sections we present the main achievements of our two research modules. The first section deals with the bearded vulture and the second with the golden eagle. A graphic abstract at the very beginning of this report shows how these materials should be used by governmental agents, policy-makers, land planners, promoters, and nature and bird protection associations.