Searcher Bias and Scavenging Rates in Bird/Wind Energy Studies


Title: Searcher Bias and Scavenging Rates in Bird/Wind Energy Studies
Authors: Morrison, M.
Publication Date:
June 01, 2002
Document Number: NREL/SR-500-30876
Pages: 9

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Morrison, M. (2002). Searcher Bias and Scavenging Rates in Bird/Wind Energy Studies. pp 9.

Evaluation of the impact of wind developments on birds (and bats) requires quantification of fatality rates because of collisions with rotating turbine blades. Such quantification requires sampling for dead animals around turbines. However, it is well known that observers vary in their ability to detect objects in the field (Morrison, Block, Strickland, and Kendall 2001). Such variation is due, in part, to innate differences in observers (e.g., physical ability or eyesight), training, and interest in the study. Searching for animals killed by turbines is inherently difficult because it often requires locating small objects in poor condition in dense vegetation (e.g., grass or shrubs) on steep terrain. Additionally, the ability of even trained observers to locate objects may change because of fatigue and extreme weather. Thus, estimates of animal fatalities in wind developments are biased to unknown degrees by inefficiencies of observers.


Estimates of fatalities are also biased by the removal of carcasses by scavenging animals or other actions (e.g., wind, plowing) before their detection by observers. All wind developments will be inhabited by various species of scavengers, primarily birds (e.g., vultures, ravens and other corvids) and mammals (e.g., squirrels, skunks, and coyotes). Thus, infrequent or unplanned surveys for carcasses can result in extremely biased and likely underestimated quantification of the impacts on animals in the development. Scavenging activity will vary seasonally because of the movement and activity patterns of the scavengers and the size of the carcass, further complicating evaluation of the influence of scavenging on collision data.


The influence of searcher efficiency and scavenging on bird/wind energy studies has been recognized (Anderson, Morrison, Sinclair, and Strickland 1999). The goal of this report is to summarize results of searcher efficiency and scavenging, thus providing a guide for workers designing or interpreting bird/wind energy studies.

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