What Do We Know about Impacts & Risk Factors to Wildlife and Habitat?
To maximize wind energy’s benefits while addressing the risk to wildlife, a first step is to better understand the extent and nature of the risk. Risk is defined as the likelihood that adverse impacts will occur to individuals or populations of wildlife as a result of wind energy development and operation. The potential impacts of wind energy to wildlife can be grouped in two categories: collision impacts, and habitat-based impacts. Impacts are studied at individual projects, but by analyzing the results of many studies we can gain insights about risk factors and potential solutions, as well as potential cumulative and population-level impacts.
What is the likelihood that adverse impacts will occur to wildlife as a result of wind energy development and operation, and what are the ecological consequences of those impacts? Risk can be defined as a function of hazard, vulnerability, and exposure, either to individual animals or to a population. Site assessment activities can provide cursory information on which species are most likely to be exposed to a particular wind energy project. Risk models and post-construction fatality data at operational projects can help us predict the wildlife impacts that might result from future wind energy projects and can also help us estimate the cumulative impacts of wind energy development on a larger scale.
Collision Risk and Risk Factors
Some birds and bats collide with wind turbines. Collision is considered a direct impact to wildlife, by which take of an individual can be linked directly to the impact source. Analyzing fatality data collected over many years and at multiple projects can help us understand which species of birds and bats are most at risk of collision, and under what conditions. By collecting data and asking research questions, we are improving understanding of what species are at risk, and where and why they are at risk, so that mitigation can be targeted where it is needed. At many wind energy facilities, regular searches are conducted for birds and bats that collided with turbines. This is often referred to as post-construction mortality monitoring (PCM or PCMM). Analyzing results from fatality studies across many facilities can give us insight into patterns of collision risk and risk factors, including how risk varies across time and space, and how specific variables, such as landscape features and weather patterns, may influence risk.
Only a small fraction of a wind facility is occupied by turbine pads and access roads, however there can be impacts to wildlife use of habitat and changes in habitat quality even in undeveloped areas. Some species avoid areas near wind energy infrastructure, regardless of the quality of the surrounding habitat. Other species may be sensitive to changes in habitat quality and fragmentation. Such changes can lead to population-level impacts if they lead to significant decreases in a survival, reproduction, and distribution. Both impacts and habituation to changes in habitat may take several years to manifest, requiring multi-year studies examining various stages of species’ life cycles and comparison of species distributions at impact and control sites.
For many species, adverse impacts from wind energy do not population-level effects. Current estimates suggest most bird species, especially songbirds, are at low risk of population-level impacts from wind energy, while longer-lived birds, like raptors, may be more vulnerable to such effects. Population-level impacts to migratory tree bats are a concern. Cave-dwelling bat fatalities are relatively low at most wind energy facilities, however major mortality from white-nose syndrome make populations of these species sensitive to impacts from wind energy. Greater access to data from all regions and better population estimates for some species are needed to better assess the effects of wind energy impacts.