Estimating habitat-related risk requires an understanding of animal behavior in response to a wind energy project and its infrastructure. Land transformation associated with development of a wind energy facility has the potential to disturb, remove, or fragment habitat for one or more species. While the physical footprint of turbine pads and related infrastructure is small relative to the total area encompassed by most wind energy projects, the scope of habitat-related impacts depends on which species are present and how they use the existing landscape, and how they are likely to respond to increased disturbance resulting from the construction and operation of a wind energy project.
Direct habitat loss from wind energy facility infrastructure is relatively small. Most permanent habitat loss is due to the roads needed to construct and service turbines. In general, projects that use existing roads have a smaller footprint than projects that require new roads.
Potentially more significant than direct habitat loss from construction is the functional habitat loss, or displacement, that occurs if animals avoid using otherwise suitable habitat around wind energy infrastructure. This kind of habitat loss can occur even if native vegetation is undisturbed. Displacement can occur if animals are disturbed by the presence of humans, by loud noises associated with construction, or even by the sight and sound of increased vehicle traffic or operating turbines. Animals might also be displaced if they associate elements of infrastructure with danger.
Some habitat impacts may be indirect, where a species is affected by changes to the habitat of other species that it interacts with, such as predators, prey, or competing species, even if its own habitat is unaffected.
How do we study habitat impacts?
Before construction begins on a project, a wildlife biologist conducts a site visit to assess the probability that species sensitive to habitat fragmentation or disturbance are using the site. If so, a more detailed field study may be warranted to document the species’ distribution, relative abundance, behavior, and daily movements as well as seasonal or lifecycle migration among specific habitats within the site. This pre-construction study provides a baseline against which to determine how the wind energy project affects particular species’ use of the site (learn more in Chapter 3).
Unlike collision impacts, which are measured in terms of fatalities, assessment of habitat impacts requires an array of measurements to account for the range of possible responses. Has the relative abundance, distribution, or behavior of animals within the project area changed? For avian species, how does the number of nesting attempts and successful hatching and fledging of young compare to before the project was built? Is survival higher or lower?
Answering these questions might require the use of radio-telemetry or GPS tracking devices that let researchers follow the movements and behavior of individuals, or extensive field surveys that provide information about the abundance of a species. Not only are these studies difficult and expensive to carry out, but they are also complicated by year-to-year background variability in these parameters. Robust study of these effects requires before-and-after comparisons of both actual project sites as well as control sites. The time and other resources required to support such research efforts typically require collaboration and dedicated funding.
What have we learned about habitat-related impacts?
Research on wind energy-related habitat impacts has focused primarily on prairie grouse, grassland songbirds, and large mammals.
Prairie grouse populations – including greater and lesser prairie-chickens, sharp-tailed grouse, and greater sage-grouse – benefit from large intact areas of prairie that satisfy all their lifecycle requirements. Prairie grouse may also serve as umbrella species, in that the conservation of their habitats benefits multiple species; decline in prairie grouse populations may indicate problems for other species that share their habitat. Because much of the current and planned wind energy development in the U.S. is in the “wind belt” – the central states between the Rocky Mountains and the Mississippi River (plus Illinois, Indiana, and Ohio) that encompass most of the range of these species – there is concern that expanded wind energy development could adversely affect prairie grouse species at the population level.
Research indicates that close proximity to roads, utility poles or lines, trees, oil and gas platforms, and/or buildings causes displacement in prairie grouse populations, and some species may avoid wind energy infrastructure during some stages of their annual cycle. However, demographic studies have not detected lower levels of survival or reproduction among prairie grouse living near wind facilities.
Like prairie grouse, grassland songbirds are a focus for habitat-related impacts because much of their range is within the wind belt. In addition, grassland birds have declined more than any other group of birds in North America, making them a high priority for conservation. Some species avoid using areas near turbines and others experience decreased reproductive success when nesting closer to turbines. For reasons not yet known, the magnitude of these effects appears to vary among species and locations.
It is uncertain whether wind energy facilities decrease habitat quality or act as barriers to landscape-level movements by big game and other large terrestrial vertebrates. One study showed that proximity to a wind facility did not affect winter survival of pronghorn in Wyoming, but it did change patterns of space use by females. Another study found that development and operation of a wind facility in Oklahoma had no measurable impact on radio-collared Rocky Mountain elk. There have not been any studies of wide-ranging carnivores, and there is no evidence to date to suggest that these animals are affected by wind energy development.
Desert tortoise & other state-identified species of concern
Long-term studies of desert tortoise at a California wind facility found survival of adult female tortoises was higher within the area of the facility than in an adjacent undisturbed area. However, fewer tortoises were using the area encompassed by the facility — an effect that became apparent only after almost 20 years of monitoring.