Sensitivity analysis of collision risk at wind turbines based on flight altitude of migratory waterbirds.
A rapid increase in wind power generation has led to bird collisions becoming a serious problem worldwide. Developing useful sensitivity maps to select low-risk sites for birds is an urgent issue. For migratory birds, such as geese and swans, that visit different habitats throughout their life cycle, it is important to conduct risk assessments that take into account their behavioural characteristics in each habitat. Geese and swans fly and migrate at varying altitudes (above the ground) ranging from 10 to hundreds of metres. Accurate predictions of avian flight altitudes are essential in assessing the risks of collisions with human-made structures. We first obtained location data for four species of geese and swans to identify their spring migratory routes within Japan (Bean Goose Anser fabalis and Anser serrirostris, Greater White-fronted Goose Anser albifrons, Tundra Swan Cygnus columbianus bewickii and Whooper Swan Cygnus cygnus). As all four species used the same roosts and overlapping foraging areas from winter to spring, a single migratory route was defined by integrating the location data of the four species. Flight trajectories were tracked using an ornithodolite. The median flight height for these four species in all landscape types was 150 m or less. Then a LASSO regression model was created with flight altitude obtained as the response variable and topographic and landscape factors as explanatory variables. Trends in flight altitude with environmental differences were similar for the four species, indicating that topographical factors strongly influence flight altitude. Finally, a statistical model was used to predict flight altitudes along migration routes. The sensitivity maps we generated showed that for all four species, most flight heights during spring were within the wind turbine range, suggesting that their risk of collision with wind turbines was greater along their migratory route. Sensitivity maps that accurately reflect avian flight characteristics help provide useful information when considering the location of further wind turbine construction.