Moose on N.D. prairies buck the trend and hold steady

Moose populations are declining in Minnesota, where biologists and wildlife managers continue to search for solutions to reversing the trend, but the majestic animals are doing well on the prairies of North Dakota.

The big question, perhaps, is why an animal associated with the boreal forest is at home on the prairie.

In a word, it might come down to disease. Or lack of it.

According to Bill Jensen, big game biologist for the North Dakota Game and Fish Department in Bismarck, the increase in prairie moose in the mid to late 1980s preceded declines in the Turtle Mountains and Pembina Hills, forested areas in the northern part of the state that offer more traditional woody habitat.

Jensen said populations in the Pembina Hills peaked in the early 1990s at about 1½ moose every two miles but declined to the point where Game and Fish hasn't offered a hunting season since 2005.

"It dramatically declined, and that mimics what was seen just across the border in Minnesota and Canada," Jensen said.

In the past two decades, northwest Minnesota's moose population has tumbled from at least 4,000 to fewer than 100 animals, the Department of Natural Resources said.

The success of moose on the prairies might come down to the relative absence of a nasty little critter called the brainworm, a parasite carried by land snails to deer and moose.

Brainworms have no effect on deer, which shed the eggs through their waste, but they're fatal to moose, Jensen said.

Brainworm correlation

In the early 2000s, Jensen said, Game and Fish sampled brains from more than 3,700 white-tailed deer shot by hunters to test for chronic wasting disease. They also checked for brainworms, and in deer hunting units 2C and 2D of northeastern North Dakota, more than 30 percent of the deer sampled had the parasite, Jensen said, while deer sampled farther west had lower prevalence rates.

The correlation would suggest more moose in the northeast also had brainworm, with fatal consequences.

"I think it really drives the system in some cases," Jensen said. "There have been all sorts of theories about why moose aren't doing well, and I think a more careful look needs to be directed at disease."

Also working in the favor of North Dakota moose is the absence of the liver fluke, another parasite. In the mid-2000s, UND graduate student Jim Maskey oversaw an extensive research project into prairie moose as part of his doctoral thesis. The risk from brainworm and liver flukes was part of the research, Jensen said.

"Liver flukes can be very damaging to a moose, but when he looked at moose livers, he wasn't finding them in North Dakota," Jensen said.

Maskey also didn't find the snails that act as hosts, Jensen said. By comparison, Game and Fish had looked at moose livers from the 1970s through the early 1990s, and found about 20 percent had the parasite.

It's only supposition, Jensen said, but a severe drought in the late 1980s might have wiped out the snails.

"The snails that are host don't survive on the drift prairie," Jensen said. "That was part of Jim's work, and he just didn't find the snails in tree rows and other places out on the drift prairie."

Free from the risk of such parasite-borne diseases, moose on the prairies are holding steady, Jensen said.

"On the drift prairie, we're only seeing about one moose per 10 square miles," Jensen said. "But we have so much drift prairie and habitat out there in the rest of the state.

"We're never going to light the world on fire with moose, but they're at a level where, for the most part, landowners are tolerant."

Living well

Jensen, who's writing a manuscript on moose growth rates, said the animals grow "really well" in North Dakota and browse primarily on woody forage, using crops such as soybeans and sunflowers less than expected.

North Dakota moose also are great wanderers, he said.

"I guess one of the things that surprises me is oftentimes, they're enough of a novelty that we get calls about them," Jensen said. "And you can almost track an individual. One day, it's up by Beulah -- a young bull, usually -- and then it's over by Hazen and down by Center and south of Mandan, and then it shows up at Flasher and then over at Carson.

"They'll just get up and go."

As more moose head west, so does the hunting pressure. Game and Fish this year offered 162 moose licenses, most of them in prairie country; Jensen said hunter success regularly exceeds 90 percent.

That doesn't ensure an easy hunt, Jensen cautioned, but there's little doubt hunters fortunate enough to draw a tag are enjoying the benefits of a stable moose population.

"We've been able in the last 10 years to maintain pretty constant harvest rates -- between 100 and 150 animals a year -- but it's primarily due to the expansion on the prairie," Jensen said. "The densities are low there, but we're able to keep bucking the trend facing other states."

Dokken reports on outdoors. Reach him at (701) 780-1148; (800) 477-6572, ext. 148; or send email to bdokken@gfherald.com .