Montana launching studies to understand bighorn sheep populations

BILLINGS – Hundreds of bighorn sheep in eight herds, along with domestic sheep, will be collared in Montana this summer as the Montana Department of Fish, Wildlife & Parks launches a large-scale study into how, or if, the animals mingle.

“We want to understand how often they interact,” said Justin Gude, Research and Technical Service Section chief for the Montana Department of Fish, Wildlife & Parks. “It’s in the best interest of domestic sheep growers and wild sheep.”

Past research has shown domestic sheep may transfer a bacteria that causes pneumonia in wild sheep if they come into contact.

The bacteria Mycoplasma ovipneumoniae can kill bighorn sheep and has also been blamed for stunting an infected herd’s population growth.

“This is a baseline type study that will elucidate useful patterns that lead to experimental introduction of management practices to reduce commingling rates,” wrote Kurt Alt, conservation director for the Montana Wild Sheep Foundation. “The previous data is pointing us toward conserving existing herds, expanding bighorn distribution and minimizing comingling and the risk of spreading pathogens.”

The comingling research will look at issues like bighorn herd size, migratory status, domestic sheep herd size and domestic husbandry practices.

The cooperative effort includes the Montana Woolgrowers Association, the Montana Wild Sheep Foundation and the Wild Sheep Foundation. Also involved is Montana State University Animal & Range Science and FWP’s wild sheep and goat working group.

One of three

The study is one of three into bighorn sheep that will take place over five years and carry a price tag of about $8 million.

Another study started last year in the Highland Mountains near Butte. Researchers are repeatedly capturing, testing and removing bighorns that continually test positive for exposure to pneumonia.

“The idea is that these chronic shedders maintain the infection in the herd,” Gude said.

The collaborative project with the University of Montana Wildlife Co-op Unit is complicated because the sheep are difficult to trap, even though the Highlands aren’t nearly as rugged as some of the other places bighorn sheep live in Montana.

Another study with UM will test FWP’s adaptive management model by making predictions – like how increasing the mountain lion harvest will reduce bighorn sheep deaths – and then updating the model when results are collected.

“Essentially, the fundamental parts of this project are to be transparent and clear about disease risks due to translocations, clarify risk tolerance at local and larger scales, and pursue new population introductions, augmentations, carnivore reductions and habitat enhancements in an adaptive management context,” Alt wrote.

Sickness

Pneumonia outbreaks have repeatedly been blamed for bighorn sheep die-offs, even though the bacteria that causes the illness can also be found in healthy herds.

A 2021 study published in the journal Ecosphere wrestled with the issue, pointing to environmental factors as contributing to bighorn die-offs.

“Our work suggests that the presence of pathogens associated with respiratory disease in bighorn sheep is insufficient on its own to account for the realized level of variation in population dynamics,” the researchers concluded.

The scientists went on to suggest, “Bighorn sheep management and restoration should focus on advancing ecological understanding of the species, rather than assume disease dynamics are predominately responsible for population trajectories.”

Retired Montana State University professor of Ecology Bob Garrott was one of several co-authors of the study. He also led two studies lasting 12 years regarding bighorn sheep in Montana and the Greater Yellowstone Area. Although he was not contacted about the new research, he praised the concept.

“An $8 million dollar investment is certainly a big deal and hopefully will advance our knowledge as bighorn restoration continues to struggle in Montana and many other western states,” he wrote in an email.

Challenges

Gude agreed it is possible there’s something about the individual animal or the environment that triggers the outbreak, conceding that scientists don’t really understand what’s going on.

For example, a herd transplanted to the Little Belt Mountains in 2021 suffered from a pneumonia outbreak, apparently without coming into contact with domestic sheep. The source herd, which lives in the Missouri River Breaks, carry the bacteria but seem healthy. What’s more, the strain that killed the Little Belt bighorns is different from that found in the source herd.

Part of the problem with transplanting sheep is that there’s no quick test to see if an animal is a carrier, Gude noted. Even though the sheep were tested before being transplanted, the test only reveals the dominant bacteria. The killer bacteria may already infect the sheep but is not flourishing, he speculated.

One theory being tested is whether dogs can be trained to sniff out the bacteria in live bighorns to alert biologists transplanting them. Another possibility is training dogs to keep domestic and wild sheep separated to avoid transferring bacteria.

The Little Belt herd has also suffered from mountain lion kills, so FWP is working with houndsmen to reduce lion populations in areas the bighorn sheep use.

“There are so few sheep now that one mountain lion could depress the population,” Gude said.

Praise

FWP’s five-year bighorn sheep project is being applauded by wild sheep conservation organizations.

“These efforts will benchmark future improvements to Montana’s bighorn sheep herds and will undoubtedly improve the distribution and health of the species,” said D.J. Berg, president of the Montana Wild Sheep Foundation.

The eight bighorn herds identified for the research include populations in the Tendoy, Highland, Greenhorn, Cabinet and Little Belt mountain ranges, as well as wild sheep in the northern Madison Range, near Gates of the Mountains and the town of Darby. It is estimated Montana is home to about 6,000 bighorn sheep.

Funding for the work comes from FWP, matched 3-to-1 by federal Pittman-Robertson Act dollars, also known as Federal Aid in Wildlife Restoration.

FWP’s share of the funding comes in large part from the annual auction of a bighorn sheep tag. Over the past 10 years, the Montana tag has sold for an average price of $348,500. The record amount raised from the Montana tag was $480,000 in 2013. Since 1986, the bighorn sheep conservation permit has raised more than $8 million, according to the Bozeman-based Wild Sheep Foundation, which auctions off the permit.