(Not so) Nice Rack: Trophy hunting causing smaller horns in bighorn sheep

Scientists are calling it a human-caused case of artificial evolution as “intense trophy hunting” is wiping out bighorn sheep populations. At least in terms of their horn size, according to a new Canadian study.

Researchers at the University of Alberta and University of Sherbrooke examined 39 years worth of data from bighorn sheep specifically from Ram Mountain near Nordegg, Alberta. For 23 of those years, the sheep were heavily hunted for their horns and the result was a dramatic evolutionary change. Selective hunting has led to a reduction in horn length by more than 20 per cent, the scientists found.

“Conventional wisdom is that the bigger your horns are, the better you do because you’re better armed than the competition,” David Coltman, professor of biological sciences at the University of Alberta, says in a statement. “This is partially true, but it’s quite age-dependent. It’s not just the size of your horns, but also how old you are. For a ram to become highly successful and socially dominant, he’s not just large-horned. He’s also experienced.”

But of course rams tend to be shot before becoming truly experienced.

“What you have here is clearly artificial selection. You can imagine that harvested animals don’t have any more offspring. Their genes are removed from the gene pool,” Coltman adds.

Bighorn sheep/University of Alberta
Bighorn sheep/University of Alberta

Biologist say “dominant rams” are at peak reproductive years between eight and 10, but that’s long after they can be legally hunted in Alberta, which is essentially when the tip of the horn is parallel with the eye.

Putting an end to hunting based on horn size will reverse the trend, but very slowly, say the scientists, who are calling for change.

“We have to be more evolutionarily enlightened about how we manage and conserve animal populations,” Coltman says.

Main Photo Alberta Fish and Wildlife/Facebook


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