Wallace P. Erickson

Avian Collisions with Wind Turbines: A Summary of Existing Studies and Comparisons to Other Sources of Avian Collision Mortality in the United States

It has been estimated that from 100 million to well over 1 billion birds are killed annually in the United States due to collisions with human-made structures, including vehicles, buildings and windows, powerlines, communication towers, and wind turbines. Although wind energy is generally considered environmentally friendly (because it generates electricity without emitting air pollutants or greenhouse gases), the potential for avian fatalities has delayed and even significantly contributed to blocking the development of some windplants in the U.S. Given the importance of developing a viable renewable source of energy, the objective of this paper is to put the issue of avian mortality associated with windpower into perspective with other sources of avian collision mortality across the U.S. The purpose of this paper is to provide a detailed summary of the mortality data collected at windplants and put avian collision mortality associated with windpower development into perspective with other significant sources of avian collision mortality across the United States. We provide a summary of data collected at many of the U.S. windplants and provide annual bird fatality estimates and projections for all wind turbines in the U.S. For comparison, we also review studies of avian collision mortality from other major human-made structures and report annual bird fatality estimates for these sources. Other sources also significantly contribute to overall avian mortality. For example, the National Audubon Society estimates avian mortality due to house cats at 100 million birds per year. Pesticide use, oil spills, disease, etc., are other significant sources of unintended avian mortality. Due to funding constraints, the scope of this paper is limited to examining only avian mortality resulting from collisions with human-made obstacles.

Mortality of Bats at a Large-scale Wind Power Development at Buffalo Ridge, Minnesota

Abstract In 1994 a major wind power development project was initiated in southwest Minnesota that may eventually produce 425 megawatts (MW) of electricity. The wind plant currently consists of 3 phases that total 354 turbines capable of generating 236 MW. During a study conducted from 1996–1999 to assess effects of wind power development on wildlife, 184 bat collision fatalities were documented within the wind plant. Hoary bats (Lasiurus cinereus) and eastern red bats (L. borealis) comprised most of the fatalities. After correcting bat fatality estimates for searcher efficiency and scavenger removal rates, we estimated that the number of bat fatalities per turbine ranged from 0.07 per y at the Phase 1 wind plant to 2.04 per y at the Phase 3 wind plant. The timing of mortalities, and other factors, suggest that most mortality involves migrant rather than resident breeding bats.

Bat activity, composition, and collision mortality at a large wind plant in Minnesota

Abstract We examined bat activity levels, species composition, and collision mortality at a large wind plant in southwest Minnesota from 15 June-15 September, 2001 and 2002. We found 151 bat casualties, most of which were hoary bats (Lasiurus cinereus). We recorded 3,718 bat passes at bat foraging and roosting areas within 3.6 km of the wind plant (x̄ = 48/detector-night) and 452 bat passes at wind turbines (x̄ = 1.9/detector-night). Peak bat activity at turbines followed the same trend as bat mortality and occurred from mid-July through the end of August. Based on the timing of fall bat migration, we believe that most bat mortality involved migrating bats. There was no significant relationship between bat activity at turbines or the number of fatalities and presence of lights on turbines. We captured 103 bats comprised of 5 species in mist nets. Big brown bats (Eptesicus fuscus) comprised most of the captures. Our study indicated that there were relatively large breeding populations of bats near the wind plant when collision mortality was low to nonexistent. Future research should concentrate on determining causes of bat collisions and methods to reduce or mitigate the mortality.

Statistical Issues in Resource Selection Studies with Radio-Marked Animals

Publisher Summary Radiotelemetry studies of animals are designed to provide insights into resource selection so that managers can obtain, protect, and restore resources used by animals. A common approach to study resource selection using radiotelemetry data involves a comparison of resource use to resource availability. Resource selection occurs when resources are used disproportionately to availability. This chapter provides a review of the study designs, statistical issues, and analytical techniques used to study resource selection and provide practical guidance for biologists, resource managers, and others conducting studies of resource selection via radiotelemetry. It also focuses on statistical issues of scale, techniques for defining resource use and availability, pooling observations, independence of relocations, and variable and model selection and how these factors affect inference in resource selection studies. In most cases, the goal of a resource selection study is to make statistical inferences to a population of animals the radio-marked sample is assumed to represent. This is achieved by considering the radio-marked animal as the experimental unit to avoid pseudoreplication, thus reducing dependency problems when individual relocations are treated as experimental units.

Analysis of count data from before-after control-impact studies

Before-after control-impact (BACI) studies are common observational studies conducted to determine environmental impacts of accidents or potential disturbances. In this paper, we present a practical guide to analysis of BACI studies when response variables are counts. Two commonly used analyses and one less common, but more appropriate, analysis are covered. The two common analyses fundamentally compare differences of differences, one using original units, the other using log-transformed units. The third analysis, which is less common, consists of estimating interaction effects in a quasi-likelihood generalized linear model with correlated errors (i.e., a generalized linear mixed model). We conclude that the two common analyses are of marginal utility when analyzing count data due to questions regarding interpretation of parameter estimates and treatment of zeros. These questions do not arise under the quasi-likelihood generalized linear model method, and it is the recommended approach. We illustrate the three techniques by analyzing data similar to that collected by an observational study of seabird counts on oiled and unoiled sites before and after the Exxon Valdez oil spill. Example data and SAS(r) code to conduct the three analyses are given.

NINE YEARS AFTER THE EXXON VALDEZ OIL SPILL: EFFECTS ON MARINE BIRD POPULATIONS IN PRINCE WILLIAM SOUND, ALASKA

Abstract We compared post Exxon Valdez oil-spill densities of marine birds in Prince William Sound from 1989–1991, 1993, 1996, and 1998 to pre-spill densities from 1984–1985. Post-spill densities of several species of marine birds were lower than expected in the oiled area of Prince William Sound when compared to densities in the unoiled area. These negative effects continued through 1998 for five taxa: cormorants, goldeneyes, mergansers, Pigeon Guillemot (Cepphus columba), and murres. Black Oystercatchers (Haematopus bachmani) and Harlequin Ducks (Histrionicus histrionicus) exhibited negative effects in 1990 and 1991. Loons showed a weak negative effect in 1993. Black-legged Kittiwakes (Rissa tridactyla) showed relative decreases in 1989, 1996, and 1998 which may have been caused by shifts in foraging distribution rather than declines in populations. Glaucous-winged Gulls (Larus glaucescens) showed positive effects in most post-spill years. Murrelets and terns showed relative increases in 1993, 1996, and 1998. Generally, taxa that dive for their food were negatively affected, whereas taxa that feed at the surface were not. Effects for some taxa were dependent upon the spatial scale at which they were analyzed. Movements of birds and the mosaic pattern of oiling reduced our ability to detect oil-spill effects, therefore our results may be conservative. Several marine bird species were negatively affected at the population level and have not recovered to pre-spill levels nine years after the oil spill. The reason for lack of recovery may be related to persistent oil remaining in the environment and reduced forage fish abundance.

Habitat Selection Using GIS Data: A Case Study

Geographic Information Systems (GIS) allow practical new approaches for the study of habitat/resource selection. In this article, we illustrate several statistical techniques that can be used in resource selection studies involving GIS with data from a study of winter habitat selection by moose (Alces alces) on the Innoko National Wildlife Refuge in Alaska. We identify statistical issues to consider when analyzing similar data. The habitat data used is a land cover map derived from Landsat TM (Thematic Mapper). Two scales of selection are considered. Maps are developed that illustrate the relative probability a resource unit is selected by moose. Bootstrapping procedures are used to estimate the final resource selection model coefficients and associated variances by using the moose locations as the basic experimental unit.

Effect of the Exxon Valdez Oil Spill on Intertidal Fish: A Field Study

Abstract The purpose of this study was to evaluate the impact of the March 1989 Exxon Valdez oil spill and subsequent cleanup activities on density, biomass, and species diversity of intertidal fishes in Prince William Sound, Alaska. Intertidal fish were sampled in a quasi-experimental, matched-pairs (oiled–cleaned versus reference sites) design stratified by three habitat types with random selection of oiled–cleaned (O–C) sites. Site pairs were sampled twice in 1990 and in 1991. Of 21 fish taxa, 5 made up 98% and 1 made up 74% of total abundance. There were no significant differences in species diversity between reference and O–C sites. Density, however, was significantly greater at reference sites for all habitats combined for both visits in 1990. In contrast, density in 1991 was about equal at reference and O–C sites. Total biomass for all habitats combined was greater at reference than O–C sites during both visits in 1990, but differences were not statistically significant. In 1991, however, the total...

Using the bootstrap and fast Fourier transform to estimate confidence intervals of 2D kernel densities

Kernel density estimators are often used to estimate the utilization distributions (UDs) of animals. Kernel UD estimates have a strong theoretical basis and perform well, but are usually reported without estimates of error or uncertainty. It is intuitively and theoretically appealing to estimate the sampling error in kernel UD estimates using bootstrapping. However, standard equations for kernel density estimates are complicated and computationally expensive. Bootstrapping requires computing hundreds or thousands of probability densities and is impractical when the number of observations, or the area of interest is large. We used the fast Fourier transform (FFT) and discrete convolution theorem to create a bootstrapping algorithm fast enough to run on commonly available desktop or laptop computers. Application of the FFT method to a large (n>20,000) set of radio telemetry data would provide a 99.6% reduction in computation time (i.e., 1.6 as opposed to 444 hours) for 1000 bootstrap UD estimates. Bootstrap error contours were computed using data from a radio-collared polar bear (Ursus maritimus) in the Beaufort Sea north of Alaska.

A Brief Response to Wiens et al., Twelve Years After the Exxon Valdez Oil Spill

Abstract We briefly address the four main issues that Wiens et al. (2001) present in their commentary on Irons et al. (2000). In summary our response is: (1) We discussed before-after control-impact design assumptions at length in our paper. Data do not exist to resolve this issue and Wiens et al. fail to shed new light on it. (2) Contrary to Wiens et al.s assertion, we discussed only statistically significant results. (3) Wiens et al. disagreed with our interpretations of a few select results. We stand by our interpretations. (4) Wiens et al. believe that the evidence we presented from other studies showing that Exxon Valdez oil still exists in Prince William Sound (PWS), and that birds are still ingesting it, is equivocal in demonstrating cause and effect. We agree, but arguments to the contrary are equally equivocal. Data from continued monitoring of marine birds in PWS support the conclusion that as of July 2000 one taxon is recovering from effects of the Exxon Valdez oil spill and eight taxa are not. Breve Respuesta a Wiens et al., Doce Años después del Derrame de Petróleo del Exxon Valdez Resumen. Nos referimos brevemente a los cuatro puntos principales que Wiens et al. (2001) presentan en su comentario sobre Irons et al. (2001). En síntesis, nuestra respuesta es: (1) En nuestro artículo abordamos de manera extensa los supuestos del diseño de evaluaciones pre y post impacto. No existen datos que permitan resolver este tema y Wiens et al. fallan en aportar nuevas ideas. (2) Contrariamente a lo afirmado por Wiens et al., solamente discutimos los resultados que son estadísticamente significativos. (3) Wiens et al. discienten con nuestras interpretaciones sobre unos pocos resultados seleccionados. Nosotros sostenemos nuestras interpretaciones. (4) Wiens et al. opinan que la evidencia que nosotros presentamos de otros estudios, que muestran que el petróleo de Exxon Valdez todavía existe en Prince William Sound (PWS) y que las aves aún están ingiriéndolo, es ambigua en demostrar causa y efecto. Coincidimos con esto, pero los argumentos en contraposición son igualmente ambiguos. Datos provenientes del monitoreo contínuo de aves marinas en PWS apoyan la conclusión que hasta julio del 2000 un taxón se está recuperando de los efectos del derrame de petróleo del Exxon Valdez y ocho taxa no lo están.