Healthy Bighorn Sheep Moms May Raise Rams With Bigger Horns, Studies Shows

Jan 18, 2018

UW Graduate Student Tayler LaSharr and UW Haub School of Environment and Natural Resources Professor Kevin Monteith examine the size of a bighorn ram's horns.

New research at the University of Wyoming shows that healthier female bighorn sheep with access to more nutritious food tend to be bigger and to raise bigger rams. The study suggests allowing hunters to kill more female bighorn sheep could reduce competition for such a nutritious diet. The study builds on other research of unhunted bighorns in California.

But right now, very few states allow female bighorn sheep to be harvested, including Wyoming. UW Haub School of the Environment and Natural Resources professor Kevin Monteith is the lead author on a paper on the subject published in The Journal of Wildlife Management in October and said the idea of permitting more ewe harvest is likely to be very controversial in the hunting community because most hunters believe horn size is genetic and that more females means a larger bighorn population.

But the new research shows hunting female sheep would leave more food resources on the landscape for other ewes, allowing them to raise rams with larger horns. He said, research shows horns are bigger when the mother is healthy.

“If mom is in poor nutritional condition and she can barely pull off provisioning her young male, that’s going to set the trajectory of growth of that male through his lifetime,” Monteith said. “And even if things get much better for him thereafter, he won’t necessarily experience those benefits thereafter. It’s termed a negative maternal effect that can be life lasting for that individual ram.”

UW Graduate Student Tayler LaSharr co-authored the paper. She said there’s still more research to be done on the benefits of fewer female bighorns in the herd.

“It’s an important step forward in understanding that it’s not just genetics that are influencing horn size,” LaSharr said. “And so we’re working on some other analyses now that looks at how harvest is influencing that and how nutrition during those different stages of life, particularly the year before an individual is born, can influence the lifetime horn size of the ram.”

LaSharr and Monteith will present these findings at a bighorn sheep working group meeting this week in Reno.