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The software tool “Evidence of Absence” (EoA) was published in 2014 to help interpret evidence that the number of fatalities of protected species (PS) that may occur at wind energy facilities has not exceeded a given threshold. The interpretation is based on the estimated probability of finding a PS carcass and the number of PS carcasses found during systematic surveys of the facilities. 

However, in years when no systematic surveys are conducted, PS carcasses are sometimes found incidentally by operations and maintenance crews in their normal course of activity. These incidental finds can represent valuable information to evaluate compliance with the Endangered Species Act and associated take permits, but including incidentals in the analyses must be done properly to avoid the introduction of bias. To address this issue, researchers evaluated three approaches to account for incidental carcasses when estimating an upper bound on total mortality using EoA: 1) excluding the incidentals from the calculation, 2) incorporating incidentals without estimating their detection probability, and 3) including the incidentals and estimating their detection probability. Authors draw conclusions about the efficacy of each under different scenarios, such as when the annual take is small and credibility level – or the chance that true mortality is less than discovered – is large.

Dalthorp, D.H., Rabie, P., Huso, M.M., Tredennick, A., 2020, Some Approaches to Accounting for Incidental Carcass Discoveries in Non-Monitored Years using the Evidence of Absence Model: U.S. Geological Survey Open-File Report 2020-1027, p. 24,

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