Wyoming’s moose populations have always varied, some dropping at alarming rates and others steadily increasing.

The Jackson moose herd went from about 3,500 animals in the early 1990s to about 500 now. The Sublette population has fared slightly better, staying relatively stagnant, while the Snowy Range herd was known for its climbing numbers.

Scientists knew some of the factors contributing to the declines: predators, wildfires and diseases such as carotid artery worms and winter ticks. They also knew moose populations were tied to food quality and abundance. What they didn’t know was how much food the animals needed before their numbers would drop, said Brett Jesmer, a University of Wyoming graduate student in zoology and physiology working with the Wyoming Cooperative Fish and Wildlife Research Unit.

“[Wyoming] Game and Fish wanted to know the cause of declines and if there was a way we could use signals in habitat, and nutrition in the animals themselves, to let us know when they have reached a population size habitat can no longer support,” he said.

Jesmer started studying Wyoming’s moose populations in the summer of 2011 using various methods including scat dogs and kidney samples. He is beginning to see connections between willow tree production and moose populations never before defined in Wyoming, and his results may ultimately help wildlife managers predict potential declines.


Moose populations didn’t roam Wyoming’s mountains and plains centuries ago like some of the Cowboy State’s other big game.

The first mention of moose by pioneers was in 1850 in the Jackson area, Jesmer said. He hasn’t found any American Indian folklore or art that references the animals.

Scientists believe they moved down from Montana into Jackson, dispersing themselves throughout western Wyoming in the late 1800s or early 1900s.

The Big Horn Mountain moose populations came from transplanted moose in the ‘50s. The Snowy Range herd migrated up from northern Colorado after a transplant in the late 1970s.

“They can definitely move quite long distances,” Jesmer said. “I’ve seen juvenile bulls, yearling bull moose, running through the prairie from the Snowies to Laramie. I don’t know where they went but can only assume they were coming from the Snowy Range.”

As moose populations aged, they produced fewer calves, causing the population to either stagnate or decline. Jesmer wondered if moose populations would essentially grow too large for their habitat, reducing the amount of good, available food and hurting the population.

Jesmer used a multi-pronged approach to his study. The researchers found more than a thousand moose droppings using scat dogs – dogs trained to find moose feces – to analyze for diet, gender and individuality. They also asked hunters to send any kidneys from moose to record fat levels.

Lastly, the group measured willow conditions in winter ranges in six herds.

Combined with data from Game and Fish on how many calves moose produce each year, Jesmer started to draw early conclusions.


Jesmer’s results, and new moose reproduction trends, are starting to support his original ideas tying moose to food abundance.

Calf numbers in the Jackson herd are increasing, said Aly Courtemanch, Jackson wildlife biologist for the Wyoming Game and Fish Department.

It’s still too early to know if the population is truly growing, but the signs are positive. In 2008, the Jackson herd had 15 calves per 100 cows. This year, Game and Fish counted 37 calves per 100 cows, she said.

“We know that when it started to decline, the willow communities were really over browsed. You could go out in to the core winter ranges for moose and see the willows looked terrible,” she said. “Now when we go out and look at then they look a lot better.”

With fewer moose eating willows, plants are recovering, offering more food, and possibly increasing moose numbers again.

The Snowy Range herd, on the other hand, might be hitting its habitat ceiling, Jesmer said. When moose first moved into the Snowies, good habitat flourished. As their numbers increased, they may have eaten too much of their available food. 

Jesmer needs to finish analyzing his data before he publishes a formal paper on the project as early as mid-2015. He also hopes to study a herd in Colorado introduced less than 10 years ago to collect additional information.

When the results are in, Courtemanch said Game and Fish should be able to use the information to better predict when moose may be running out of food. Wildlife managers will then know to either increase hunting licenses or use habitat treatments to improve food sources, she said.

“We’re probably never going to get back to 3,500 moose. That was before the recolonization by large predators, and large scale habitat changes like 1988 Yellowstone fires,” she said. “But hopefully in the coming years we will continue to see some improvement.”

Reach Open Spaces reporter Christine Peterson at 307-746-3121 or christine.peterson@trib.com. Follow her on Twitter @PetersonOutside.




Load comments