Strychnine and Consequences

A copy of the Yukon wolf conservation and management plan, written in 1992, fell into my hands today.  On page 3 of the plan, the unintended wider effects of wolf slaughter campaigns in the 20th century are highlighted:

“During the 1920’s, strychnine poisoning of wolves was first allowed in the Yukon….Government poisoning programs started in the 1950’s when up to 154 strychnine poison baits were set out in the southern Yukon each winter. Between 1957 and 1967, a total of about 600 wolves were killed and many other animals were accidentally killed, including more than 150 wolverines.”

Mike Schwartz of the Rocky Mountain Research Station published a paper on wolverine genetics, estimating that the effective population of US Rockies wolverines – that is, the number of wolverines contributing to the gene pool –  is somewhere between 28 and 52 animals. Most of these are in Montana and Idaho. Wyoming holds six or seven known wolverines. Colorado is home to one. We couldn’t lose 150 wolverines, because there are probably barely that many in the US in the first place.

Wolverines are more widespread in northern Canada than they are in the Lower 48, but 150 unintended deaths in the course of a decade still seems substantial. Strychnine and other poisons were widely used in wolf and coyote eradication campaigns in the US, and there is speculation, even beyond the wolverine research community, that the poison baits intended for other predators eliminated wolverines from the US Rockies and the Sierras. The range expansion that we are seeing now, as wolverines make their way to Colorado and California, is, according to this theory, part of a decades-long recolonization process as Canadian and then Montanan wolverines make their way south. In one sense, then, the story of wolverines in the US Rockies in the 21st century is a story of a resilient species making its way home in the wake of astonishingly irresponsible human behavior. And it took little human effort; all we needed to do was stop interfering.

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