10-year Montana study reveals moose insights, and some surprises

BILLINGS – Moose numbers are stable to increasing in three regions selected as representative of Montana’s moose population, concluded a 10-year study conducted by Montana Fish, Wildlife & Parks.

“So that was certainly good news,” said Nick DeCesare, an FWP biologist and lead scientist for the study.

Statewide, moose abundance based on hunter surveys was estimated at between 9,800 and 11,700 animals, with moose numbers averaging 10,380 between 2012-2016 and 2021-2023.

“Statistical estimates of abundance at this scale are unprecedented for moose in Montana and are encouraging for long-term monitoring over space and time,” concluded the study’s final report, “Ecology, population dynamics, and monitoring of moose in Montana.”

Started in 2013

The FWP study was launched in 2013 as moose strongholds, like Minnesota, were seeing populations of the big, odd-looking ungulates crash.

In Montana, there were reports of moose rubbing off their fur seeking relief from heavy tick loads. Necropsies of dead moose were revealing infestations of worms in their arteries. Hunters were worried about the increase in predator populations as wolf and grizzly bear populations rose. And as a cold-adapted species, moose were facing shorter and warmer winters with less snow.

“I think when we were going into the study there really were some alarm bells sounding in Montana and in other parts of the Lower 48 where moose are kind of at that southern extent of their range,” DeCesare said.

Details

The 184-page report, now posted on FWP’s website, focused on cow moose populations in three areas: the Cabinet-Salish mountains in northwest Montana, the Big Hole Valley in the southwest and the Rocky Mountain Front.

“There’s sort of different stories playing out in each area,” DeCesare said, because of variations in habitat, predators and rates of infection from parasites like winter ticks and arterial worms.

To find answers, the researchers made 229 captures of 193 adult female moose, attaching VHF- and GPS-telemetry collars to their necks to track the animals’ movements.

“One big take home we saw was there’s just kind of a consistent effect of nutrition on how well they’re doing in all aspects of their dynamics,” DeCesare said. “The survival of the adults was higher for animals in better nutritional condition, their ability to produce young every year was higher, and that includes both getting pregnant and having twins. And then we see a similar sort of pattern in the survival of calves, where animals in better condition are having higher quality calves that are living longer.”

DeCesare calls moose “selective generalists” when it comes to their dining preferences, with shrubs like willow and, in northwestern Montana, wild lilac making up a large part of their diet.

“Across their range, they can eat a lot of different foods,” he said. “But within a given local area, they can be pretty picky about what they’re eating.”

Of the different types of willow the scientists sampled for the study, DeCesare said summer forage was “the most correlated to how productive” the cow moose were.

Parasites

One of the biggest concerns going into the study was that Montana’s moose population may be facing serious threats from parasites, especially winter ticks and arterial worms.

Although winter ticks are taking a toll on moose populations in the northeastern United States, DeCesare and his colleagues weren’t commonly seeing similar afflictions in Montana. The captured animals with the highest tick loads were those living in areas with denser moose populations, shared winter range with deer and elk, decreased snow cover during fall and spring and warmer temperatures during spring and summer. This data came from pooled research with five other western states, the report noted.

The potential for less snow in the spring has “perhaps the highest potential” to lead to higher tick infections of moose across the West, the study said.

“The arterial worms are harder to study because an animal has to die to allow you to inspect their carotid arteries to know that they’re infected,” DeCesare said.

The worms, formally known as Elaeophora schneideri, were prevalent in moose found dead, the report showed.

“It’s still not so severe that those populations aren’t stable,” DeCesare said. “We don’t have an in-depth understanding of how arterial worms are affecting moose in ways that don’t just kill them, but there are results in that report to show that higher loads of those arterial worms are associated with mortality of these adult moose, especially in in the Big Hole study area.”

Predators

Based on camera traps that snapped more than 2.5 million images, the highest densities of black bears and wolves were found in the Cabinet-Salish study area. The region had the lowest calf survival rate (.36) of the three study areas. At birth, calves may weigh 25 to 35 pounds.

There were more grizzly bears along the Rocky Mountain Front, yet it had the highest calf survival rate (.41). Mountain lions were equally dense in the Cabinet-Salish and Rocky Mountain Front.

The adult moose studied were more likely to die from health-related mortalities (7.5% annually) than by wolves (1.1%), grizzly bears (.1%) and mountain lions (.1%). Human predation was higher (around 2%) in the Big Hole Valley where cow moose can be hunted, compared to an average of 1.4% hunter-caused mortalities annually in the other regions.

In comparison, about 1% to 3% of the studied moose were killed each year by arterial worm infestations.

When the researchers simulated a 30% reduction in predator densities, there was a “relatively minimal” predicted uptick in moose numbers.

Populations

One of the main goals of the study was to improve FWP’s understanding of a cost-effective means to monitor moose populations. The research showed that aerial counts of moose aren’t a great way to estimate their population because there’s so few of them, they are spread out on the landscape and although large animals, moose are great at hiding.

When trying to locate some of the collared cows, the researchers would be flying over small stands of willow bushes and still not see the moose. One technique the study explored to estimate moose populations was to survey deer and elk hunters, who account for more than 2 million days afield. The report called them “a tremendous workforce afield for monitoring wildlife.”

During FWP’s annual hunter harvest phone surveys the researchers were able to collect and map an average of 2,901 moose observations per year across eight years.

Experiments by FWP are also underway using camera traps in northwestern Montana to estimate moose, deer, elk and bear populations, but DeCesare said it’s proving to be a labor-intensive process.

Unique discoveries

Among the unusual discoveries made during the study was a 16-year-old bull moose shot by a hunter in 2012. The animal was aged by its tooth. A moose over 12 years old is unusual, DeCesare said, although a few 13- and 14-year-olds were recorded.

Several cow moose in the Libby area also made it to 16 and even 17 years old, including one that was still alive when the study ended last year – the oldest aged moose in northwest Montana.

The researchers collared 30 moose in each study area, with three from the Rocky Mountain Front taking long walks into Eastern Montana. One meandered 528 miles. Two others traveled 279 and 310 miles.

“Two of them made these big movements during the summer out into Eastern Montana towards Square Butte, and the other one up towards Havre, but then came back,” DeCesare said. “So it was sort of like a summer migration.”

One collared moose wandered into Canada before its collar failed, so there’s no telling how far it may have trekked.

The long-distance walks may be prompted by moose reaching their threshold for density along the Rocky Mountain Front, DeCesare speculated.

“It could be a signal if they’re starting to sort of saturate that habitat, that some of them are starting to look elsewhere, but it’s just a handful,” he said.

The researchers also examined whether the United States’ southernmost moose were a different subspecies. Research of their DNA showed moose migrated to North America about 15,000 years ago and are all related.

“This weakens the case for taxonomic recognition of a long-standing southern subspecies of moose in the range of A. a. shirasi,” the researchers noted.

Moose may have been living in Montana for only a few hundred years, DeCesare said, which would explain why they are struggling to adapt to parasites other wildlife have adjusted to over thousands of years.

Montana’s moose were nearly eliminated by unregulated hunting in the early 1900s, when only 100 were estimated to remain. Southwestern Montana was recolonized by moose moving in from Wyoming and Colorado, DNA analysis showed, while northwestern Montana’s moose are more closely related to animals from British Columbia.