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Data Series 881

Evidence of Absence Software User Guide

By Dan Dalthorp, Manuela Huso, David Dail, and Jessica Kenyon


Evidence of Absence software (EoA) is a user-friendly application used for estimating bird and bat fatalities at wind farms and designing search protocols. An updated version published in 2017 is available as Data Series 1055 (see link on right). The software is particularly useful in addressing whether the number of fatalities has exceeded a given threshold and what search parameters are needed to give assurance that thresholds were not exceeded. The software is applicable even when zero carcasses have been found in searches. Depending on the effectiveness of the searches, such an absence of evidence of mortality may or may not be strong evidence that few fatalities occurred. Under a search protocol in which carcasses are detected with nearly 100 percent certainty, finding zero carcasses would be convincing evidence that overall mortality rate was near zero. By contrast, with a less effective search protocol with low probability of detecting a carcass, finding zero carcasses does not rule out the possibility that large numbers of animals were killed but not detected in the searches. EoA uses information about the search process and scavenging rates to estimate detection probabilities to determine a maximum credible number of fatalities, even when zero or few carcasses are observed.

First posted September 19, 2014

For additional information, contact:
Director, Forest and Rangeland Ecosystem Science Center
U.S. Geological Survey
9777 NW 9th St., Suite 400
Corvallis, Oregon 97330

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Suggested citation:

Dalthorp, Dan, Huso, Manuela, Dail, David, and Kenyon, Jessica, 2014, Evidence of absence software user guide: U.S. Geological Survey Data Series 881, 34 p.,

ISSN 2327-638X (online)




Installation Instructions

Getting Started

Statistical Approach and Terminology

Data Management

Analysis and Interpretation: A Tutorial


References Cited

Appendix A. Accounting for Uncertainty in Searcher Efficiency and Carcass Persistence

Appendix B. Choice of Representative Interval Length for Calculating

Appendix C. Parameterizations of Distributions Used in the Software

Appendix D. Using Previous Year’s Search Data to Inform Current Year’s Prior Distribution

Appendix E. Using Several Previous Years’ Data to Inform Current Year’s Prior Distribution

Appendix F. Estimating Total Number of Fatalities Over Several Years (or Several Sites)

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