Wind energy development is occurring in Oregon and Washington within the Columbia Plateau physiographic region (ecoregion). With this development comes the potential for direct impacts to birds and bats through collision mortality and for indirect effects through habitat fragmentation or displacement of birds and other wildlife. Collision mortality is well documented at most wind energy facilities, but population level effects have not been detected, although few studies have addressed this issue. The purpose of this report is to estimate cumulative impacts associated with wind energy development projected to occur within the Columbia Plateau Ecoregion (CPE) of eastern Washington and Oregon through 2015. This report updates two previous versions to account for additional bird and bat fatality estimates from several wind energy facilities where monitoring reports recently became available. For the purpose of this analysis, we assumed that for cumulative impacts to occur, there must be a potential for a long-term reduction in the size of a population of birds or bats. When assessing the potential for cumulative impacts, it is necessary to first define the population potentially affected by wind energy development. Because birds and other animals do not recognize geopolitical boundaries, we have defined the affected population as those birds and bats of each species that breed, winter, or migrate through the CPE. As of December 14, 2010, there were 4,059 megawatts (MW) of installed wind energy in Washington and Oregon, most of which is within the CPE. For this analysis, we assumed that 6,700 MW of wind power would be present in the CPE.
This cumulative effects analysis used data from 25 year-long monitoring studies conducted at 23 wind energy facilities in the CPE, as well as preliminary carcass composition data from two additional facilities with post-construction monitoring data. For this analysis we assumed that the bird and bat communities are similar across all wind energy facilities because of habitat and land use similarities throughout the CPE, and thus data from existing facilities are applicable to proposed facilities in this same ecoregion. To define population sizes of those species most likely to be affected by wind energy development in the CPE, we used data from a Partners in Flight publication that estimates breeding population size of bird species in the CPE.
To predict raptor, all birds (excluding raptors), and bat mortality for 6,700 MW of wind energy development in the CPE, we assumed it would be similar to the other existing wind energy facilities in the CPE. Therefore, we estimated raptor mortality by multiplying the number of MW (6,700) by 0.08, the mean number of raptor fatalities/MW/year at the existing facilities. We multiplied the total number of MW by 2.28 fatalities/MW/year (the mean among the 22 CPE wind energy facilities) to estimate all bird mortality (excluding raptors), and by 1.14 fatalities/MW/year to estimate total bat mortality. To estimate total cumulative mortality by bird or bat type and/or species, we assumed the fatalities associated with 6,700 MW of wind energy would have the same species composition as fatalities found at existing wind energy facilities in the CPE.
Ninety-eight species of birds are represented among the 1,183 bird fatalities reported at existing wind energy facilities in the CPE. For all birds combined, we estimate that total annual mortality in the CPE would be 15,276 birds/year. Despite several thousand bird fatalities from 6,700 MW facilities, raptors would compose 8.7% of the fatalities, passerines would compose approximately 69.5% of the fatalities, upland game birds would compose 13.1%, doves/pigeons would compose 3.8%, waterfowl/waterbirds/shorebirds would compose 2.1% and other bird types, such as woodpeckers, nighthawks and swifts, would compose 2.7%. Approximately 4.5% of the mortality would be composed of non-protected European starlings, rock pigeons and house sparrows.
We estimate total raptor mortality in the CPE would be 536 fatalities per year. American kestrels account for 29.0%, red-tailed hawks account for 22.0%, Swainson’s hawks account for 9.0%, and short-eared owls account for 8.0% of the raptor fatalities recorded at the regional wind projects studied. Assuming this trend holds true for all proposed wind energy facilities in the CPE, and assuming there would be 536 raptor fatalities per year, it would be expected that on average 155 American kestrels and 118 red-tailed hawks would be killed each year. The other species of raptors occurring in the CPE have had no or fewer fatalities at existing wind energy facilities, and would likely represent a much smaller number of fatalities. Three species of concern in the region, golden eagle, ferruginous hawk and Swainson’s hawk, have all been found as turbine collision victims in the CPE. Ferruginous hawks have composed 4.0% of the raptor fatalities, Swainson’s hawks have composed 9.0%, and golden eagles have composed 1.0%. Assuming a total of 536 raptor fatalities could occur each year in the CPE, this would result in 21 ferruginous hawk, 48 Swainson’s hawk, and five golden eagle fatalities per year.
Annual collision mortality in the CPE would represent approximately 0.06% of the breeding population of American kestrels and 0.11% of the breeding population of red-tailed hawks. Background mortality for these species is much higher than this estimate and the additional wind energy related mortality is likely insignificant from a population standpoint. Given our estimate of 21 ferruginous hawk fatalities on an annual basis, even if all turbine mortality occurred to resident breeding adult birds, this would represent 2.1% of the breeding ferruginous hawks in the CPE. Because mortality would likely be spread out among migrants, winter residents, resident breeders, and juveniles, as well as adults, mortality of adult ferruginous hawks actually breeding in the CPE would be less than 2.1%, likely on the order of 1–2%. Given published annual mortality rates for adult ferruginous hawks of 24–30%, additional losses of 1– 2% of resident breeders associated with 6,700 MW of wind energy development in the CPE would not likely have measurable population consequences. Given our mortality estimate of 48 Swainson’s hawks per year, this would represent only 0.48% of the Swainson’s hawks in the CPE. Compared to many other raptor species, there is little data on annual survival of Swainson’s hawks. The annual mortality rate of Swainson’s hawks was reported in one study from western Canada, where it was estimated to be 15.7%, and nestling mortality rates ranged from 56–81% over the multi-year study. Given estimated Swainson’s hawk mortality rates of 15.7% for adults and 56-81% for juveniles, additional losses of <0.5% would be considered sustainable and would not have measurable population consequences. Given our annual estimate of five golden eagle fatalities, even if all turbine mortality occurred to resident breeding adult birds, this would represent 0.3% of the breeding golden eagles in the CPE. It has been estimated that only 50% of golden eagles survive to the age of three years. Given these published mortality rates for golden eagles, additional losses of <0.3% of the population associated with 6,700 MW of wind energy development in the CPE would not likely have measurable population consequences for golden eagles. Using similar analyses of estimated fatality rates, population sizes in the CPE, and published annual mortality rates for upland game birds, waterbirds, waterfowl, shorebirds, passerines, and sensitive bird species, it is unlikely that population consequences would be expected for these avian groups if 6,700 MW of wind energy was developed in the CPE.
Using the mean bat mortality estimate of 1.14/MW/year at regional wind energy facilities within the CPE, total bat mortality in the CPE was estimated at 7,638 per year. Based on species composition of bat fatalities found at CPE wind energy facilities, approximately 3,798 silver-haired and 3,670 hoary bat fatalities would occur in the CPE on an annual basis.
Unlike birds, there is little information available about population sizes of most bat species, especially the non-hibernating, solitary tree-roosting species that compose most of the wind energy facility related mortality in North America. The significance of wind energy impacts on hoary and silver-haired bat populations is difficult to predict, as there is no information available on the overall population sizes of these bats. However, hoary and silver-haired bats are widely distributed throughout North America. Most concern over impacts to bats is with wind energy facilities built on ridgetops in the Appalachian Mountains, where mortality levels have been as high as 39.7 bat fatalities/MW/year, substantially higher than the average of 1.14 bat fatalities/MW/year observed in the CPE. In general, mortality levels on the order of one to two bats per MW are likely not significant to populations, although cumulative effects may have greater consequences for long-lived, low-fecundity species such as bats.
Grassland and shrub-steppe communities are the most abundant native communities in the CPE, but they are also highly subjected to development and conversion to agriculture. In addition to potentially thousands of new vertical structures, added wind energy generation in the region will result in more roads (mostly dirt and gravel) and increased human activity due to turbine construction and maintenance. A substantial portion of these impacts will be to already heavily-disturbed agricultural fields and moderately disturbed rangeland used for livestock grazing. The percent of direct impacts actually occurring in native grassland or shrub-steppe habitat are difficult to predict and would be based on individual facility design and layout. However, based on the community types that existing and proposed wind energy facilities are located in, approximately 48% of the existing and proposed facilities would be in cultivated cropland. Assuming that on average the permanent impact associated with a turbine and the associated access roads is 0.74 acres per MW, then approximately 2,578 acres (4.0 mi2 ) of non-agricultural vegetation types, primarily grassland and shrub-steppe vegetation, would be lost in the CPE with 6,700 MW of wind energy. These impacts would be spread over a large area geographically. Given that the CPE is 32,096 mi2 in size, permanent impacts associated with 6,700 MW of wind energy development would represent only 0.01% of the area, with nearly half of this occurring in cultivated cropland.
Habitat loss associated with wind energy development is not expected to be a significant loss to any given species within the entire CPE. However, because existing and proposed wind energy facilities tend to be concentrated within certain regions within the CPE, habitat loss may lead to localized population declines of some species.
Avian population estimates used in this analysis relied on those developed by Partners in Flight (PIF) using breeding bird survey (BBS) data, and some of these estimates had relatively large standard errors. Because BBS data were designed to detect long-term population trends, use of these data for estimating population sizes has been questioned. Regardless of these concerns, in order to estimate cumulative impacts, information on sizes of affected populations is required, and the population estimates provided by PIF are the only ones available for the CPE. While these estimates may not be completely accurate for all species, they are the only ones available and therefore represent the best available data for this use.
Finally, this cumulative impacts assessment only examined cumulative impacts of birds and bats due to wind energy development in the CPE. Wind energy development is only one factor affecting wildlife populations in the CPE, and is likely minor compared to other past, present, and future actions in the CPE, including large-scale conversion of native shrublands and grasslands to crop land; expansion of urban areas and rural subdivisions; road and highway construction; energy development, including dams for hydropower; and increases in other infrastructure, such as communication towers and power lines. The ability to estimate wind energy development impacts on wildlife is unique because several studies have been conducted in the CPE to quantify bird and bat impacts and monitoring of fatalities is typically conducted for wind energy development. This is not done for any other type of development. Similar estimates of bird and bat impacts due to direct mortality and loss or fragmentation of habitat caused by other activities are not available. Also, this analysis does not account for the beneficial impacts on habitat from wind energy development, both from adding value to land and thus preserving it from subdivision and further habitat fragmentation, or from replacing fossil fuel sources, and its associated greenhouse gas emissions and ensuing habitat impacts.