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Moose thriving on North Dakota prairie

A cow moose stands in a field southwest of Gardner, N.D., and just west of Interstate 29 in 2005. Forum file photo

BISMARCK - 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, University of North Dakota 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.