Collisions of birds with wind turbines are a focal point when discussing the implications of renewable energies on nature conservation. The project “Prognosis and assessment of collision risks of birds at wind turbines in northern Germany” (PROGRESS) focused on the extent and consequences of bird mortality at wind turbines.
Collision victims were searched in five search efforts from spring 2012 to spring 2014 (three spring and two autumn field searches of 12 weeks). 46 different wind farms were examined. The total searched transect length amounted to 7672 km. With a total of 291 birds found, an average of one bird was found every 27 km. Common bird species with habitat use (feeding and staging) of the wind farm area prevail the list of fatalities found. Birds of prey did not dominate the list. Nocturnal broad front migratory songbirds (especially thrush species) were hardly represented among the fatalities. The total number of fatalities was estimated incorporating search efficiency and carcass removal experiments.
An extrapolation of the results for the entire project area leads to an annual mortality of around 8500 Common buzzards, 11,300 Wood pigeons and 13,000 Mallards. Based on the breeding population in the project area this translates to 0.5% of Wood pigeons, 5.0% of Mallards and 7% of Common buzzards (assuming 50% floaters).
Results of vantage point watches indicate that the species-specific collision risk with wind turbines largely differs between species as a result of clear behavioural differences.
For the vast majority of wind farms the numbers of collision victims predicted by the Band-model were clearly below the number of collision victims estimated from carcass searches. The suitability of the Band-model for the evaluation of an anticipated collision risk for a planned wind farm at an ‘average’ onshore site is limited.
Four modelled populations of Common buzzard in northern Germany are predicted to decline when incorporating the median estimates of additional mortality derived from fatality estimates.
Statutory species protection conflicts might not always be adequately solvable for an individual project. Therefore, overarching solutions are required to accompany the further expansion of wind farms, which ensure that this does not lead to a severe decline of certain bird species that are particularly affected by collisions. Specifically, the following strategies need to be addressed:
Large-scale wildlife conservation programs e.g. for Red kites and Common buzzards that improve habitats, particularly in terms of food availability
Identification of species-specific density centres that are of particular importance as source populations, and assessing targeted measures to protect and promote them,
Development of concepts and practical testing of a post-construction species protection support in terms of their effectiveness and their economic effects.
Increased research efforts in terms of scale and addressing cumulative effects.