Field & Stream Online Editors
Field & Stream Online Editors

The 300 Wyoming elk that suffered paralysis and death over several weeks this winter appear to have succumbed to toxins in lichen.

Tumbleweed shield lichen, Xanthoparmelia chlorochroa, is common in Wyoming’s arid lands, but it contains usnic acid, which most likely proved fatal to wintering elk. After finding the lichen in the rumen of afflicted elk, scientists with the Wyoming Game and Fish Department gathered a truck load and fed it to three captive elk. Two quickly went down with the same muscular weakness that dropped elk across Wyoming Red Rim Daley Unit in early February.

But with the answer came more questions: Is the lichen always this toxic? Why these elk? A native herd spent the winter 15 miles north in the same drainage and remained healthy.

“One of the hypotheses is that elk may be able to detoxify small amounts of this lichen,” says Dr. Walt Cook, a Game and Fish veterinarian. “But the elk that died don’t normally winter in that location and they ate a lot of lichen ¿¿¿ some rumen contents were 50% lichen ¿¿¿ so maybe they weren’t able to process it.”

Winter storms drove the elk to wind-blown ridges where drought-stricken foraging conditions were poor and lichen was one of the few choices. Usnic acid, used in diet supplements and proven to cause liver damage in humans, is known to exist in the lichen but scientists are seeking a direct link to the elk’s symptoms. So while newspapers went for the quick answer and baffling headlines (“Diet chemical may have killed elk”), Dr. Merl Raisbeck of the Wyoming State Veterinary Laboratory went to work in his chemistry lab.

“Compounds that cause liver damage don’t usually cause muscle damage,” says Raisbeck. “The only way to be 100% certain (about the lichen) is to extract the compounds from the lichen and go the full testing cycle.”

That could take a year to five years and will run up a hefty tab. Hunting restrictions for the area near Rawlins are likely while biologists try to determine if there is any continuing threat to the elk and, if so, what to do about it. The options are few: improve forage conditions and haze the animals away from suspect areas if more die-offs occur.

“That’s extreme,” says Cook. “So it’s important for us to identify exactly what happened out there.”