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Gray Wolf Poaching Underreported in Wisconsin

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Treves, A., Langenberg, J. A., López-Bao, J. V. & Rabenhorst, M. F. (2017). Gray Wolf Mortality Patterns in Wisconsin from 1979 To 2012. Journal of Mammalogy, (February 6th embargo data).

Main points

  1. 1. We investigated causes of death of 937 gray wolves in Wisconsin from October 1979 to April 2012. We discovered that poaching (illegal killing of wolves) was the most common cause of death. We documented that wolf population growth slowed by 4% in each of the last few years as a result of increased mortality.
  2. From 431 deaths and disappearances of radiocollared wolves aged > 7.5 months, we estimated human causes accounted for two-thirds of reported and reconstructed deaths, including poaching in 39–45%, vehicle collisions in 13%, legal killing by state agents in 6%, and nonhuman causes in 36–42%. Poaching risk for wolves without radio collars appears to have been even higher.
  3. Most poaching went undetected by the government as revealed by the high proportion of missing radio-collared wolves (56%) that went off the air after an average of 529 days, similar to that for poached wolves (558 days); by contrast, the average intervals for wolf deaths of nonhuman cause and vehicle collision were 685 and 778 days, respectively.
  4. When the government did recover wolf carcasses, the agencies systematically under-estimated poaching by more than 5% and possibly more than 11%. Two forms of scientific bias explain the under-estimation. The first – sampling error – occurred when the government radio-collared wolves in core areas of the wolf range where wolves experience less mortality overall and especially less human-caused mortality. We also found measurement error when poaching was missed by the agency and assigned to another cause of death. For example, a subsample of radiographed wolf carcasses revealed that 37% of vehicular collisions also included metal consistent with gunshot wounds.
  5. We reconstructed the fates of missing wolves and estimated that wolves without radio-collars experienced 28% higher rates of mortality (per capita hazard) than did radio-collared wolves. That presents a scientific challenge because official estimates of population dynamics have always been based on radio-collared wolves. These population estimates will require re-evaluation in light of the new data.
  6. Current population estimates published by the sate of Wisconsin have not been peer-reviewed by independent scientists, which is a problem exacerbated by a change in state methods for wolf census and less transparency after 2012. The expansion of hound use and failure to verify the accuracy of civilian and DNR trackers raises a possibility that trackers are counting hounds or even coyotes and calling them wolves.
  7. Poaching animals is not only something happening to elephants, tigers, and rhinos in distant continents; it is the major cause of death of gray wolves in Wisconsin and elsewhere in the U.S. i.
  8. Our analysis differs from others and government reports because we offer the full dataset free to the public for independent scrutiny.

i. For related articles, Treves, A., Krofel, M. & Lopez-Bao, J. V. (2016). Missing wolves, misguided policy. Science (Eletter) 350, 1473-1475.

Download PDF: Treves_etal_2017_maintext_only

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