Why are bighorn and domestic sheep hanging out? Here's why we should care.
A respiratory illness common in domestic sheep can devastate wild bighorn sheep herds. Now a pair of MSU researchers is studying how wild and domestic sheep interact.
Researchers at Montana State University have been studying the domestic and bighorn sheep interactions, but recently received $4 million in university funding to initiate the latest research. Photos by Diane Renkin and Martin Schmidli. Illustration by Julia Barton
EDITOR'S NOTE: This article has been updated to include statements and context from FWP
disease ecologist Emily Almberg.
by Julia Barton
The bighorn sheep is a muscular and athletic denizen of
mountainous and arid terrain across the western U.S. This hardy ungulate is also
remarkably susceptible to diseases spread by their wooly, domestic
counterparts. In an effort to mitigate the spread of disease, a new research
project in Montana aims to better understand where and how often wild and
domestic sheep interact.
Montana State University has been studying bighorn and
domestic sheep in Greater Yellowstone for years, according to MSU Extension
wildlife specialist Jared Beaver, who explained that research involves a
variety of stakeholders including conservationists, state agencies, hunters and
livestock owners. The university awarded $4 million to kickstart the latest round
of research, led by Beaver and MSU Extension sheep specialist Brent Roeder in
collaboration with Montana Fish, Wildlife and Parks.
“Oftentimes with very complex and nuanced wildlife issues,
it's easy to see if it's an ecological or biological question,” Beaver told Mountain Journal. “But when you have a
lot of stakeholders invested, there's a lot of social and cultural components
to it as well, and it makes these studies very dynamic.”
Symptoms related to the bacteria M. ovi are typically mild among domestic flocks of sheep, but can be devastating to wild bighorn herds.
The disease prompting this research, and other similar studies, is a respiratory illness caused by
Mycoplasma ovipneumoniae bacteria, or M. ovi for short, that can cause
pneumonia in sheep and goats, and predispose animals to other respiratory
complications. Symptoms are typically mild among domestic flocks, though they’ve
caused substantial economic losses for livestock producers. Impacts on wild
herds can vary drastically, ranging from mild to “devastating,” according to
Beaver.
Respiratory diseases have likely been present among bighorn
sheep since domestic sheep were first brought to the U.S. in the 15th
century, said FWP disease ecologist Emily Almberg. The pneumonia found
in sheep is polymicrobial, meaning various bacteria are present in sick animals,
and it was unclear what the causative agent was until M. Ovi was linked to the
disease in the early 2000s.
“Not all disease introduction events result in massive die-offs,”
Almberg said. “We have documented M.
Ovi introductions that cause no detectable disease. The majority of them, as
far as we know, seem to cause some disease … you can have very catastrophic
impacts to some herds where they lose 50 to 70 percent of the herd.”
At least 22 epizootics, or outbreaks,
among 43 herds were documented in Montana between 1979 and 2013, according to a 2015
paper.
"[M. ovi introductions can] have very catastrophic impacts to some herds where they lose 50 to 70 percent of the herd.”
–
Emily Almberg, Disease Ecologist, FWP
There are two approaches for disease transmission research,
according to Beaver. The first explores ways to improve the health of chronically
infected herds. A successful example of this work has been removing members of
a herd that continually test positive for M. Ovi baceteria, Almberg explained. The
second focuses on minimizing contact in the first place.
“Our work falls in the latter category because that has the
potential to yield wins for both bighorn and domestic sheep,” Beaver said.
“It's a first step of what we hope will start to involve other researchers that
are looking at improving performance of chronically infected herds.”
Once the details of how interactions between wild bighorns and
their privately-owned kin are better understood, land managers with Montana
Fish, Wildlife and Parks can tailor management protocol to minimize
interactions and subsequent disease transmission, according to Beaver. The
current recommendation is to keep roughly nine miles between domestic and wild
herds.
“As the landscape becomes increasingly more populated and
fragmented, allowing for that much space really isn't always feasible,” Beaver
said. “It's certainly not feasible if we want to continue to try and restore
bighorn sheep numbers across the West, so our first step is simply getting a
better understanding of how contact is occurring.”
The MSU endowment will fund researchers and GPS collars to
track movement of bighorn sheep, domestic sheep and livestock guardian dogs.
Beaver emphasized the collaborative backbone of the project, which will take
account of anecdotal evidence from long-time livestock producers in the state
and involve other stakeholders as needed. And it’s starting here in the
Treasure State.
“Montana is leading the charge,” Beaver said. “The ultimate
hope for everyone involved is that we can find adaptive management strategies
that benefit wildlife managers, producers and the wild and domestic sheep
themselves.”
Mountain Journal is the only nonprofit, public-interest journalism organization of its kind dedicated to covering the wildlife and wild lands of Greater Yellowstone. We take pride in our work, yet to keep bold, independent journalism free, we need your support. Please donate here. Thank you.
About Julia Barton
Julia Barton is a freelance journalist and communications specialist based out of Bozeman. A Montana native, she earned a journalism degree from the University of Southern California and reports on the environment, outdoor recreation and the arts.
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