The Mystery of the Disappearing Moose

By Greg Breining

Minnesota’s moose are dying, and Bill Severud ’02 wants to know why.


Looking at a laptop screen, researcher Bill Severud ’02 traces the recent zigzags of a radio-collared moose, first with her collared calf, and then without. “This is where I think trouble happened,” he says, pointing to a spot on the shore of a small lake in northeastern Minnesota, several miles from his Isabella, Minnesota, research station. “She came back to the kill site a second time and a third time.”

An hour later, Severud and his colleagues are outdoors with an antenna and receiver, trying to locate the calf’s still-beeping collar. They follow the signal to the lakeshore, where they find the bloody skull and mandible of the young moose. Nearby is the radio collar, where they figure a wolf dropped it. “It’s a puzzle trying to piece it all together,” says Severud. “And then we get up here and see the evidence.”

Severud, who majored in biology at Carleton and is now a graduate student in wildlife ecology and management at the University of Minnesota, is finding plenty of chances to piece together the mystery of how and why moose die. He is part of a team of researchers from the Minnesota Department of Natural Resources (DNR) and the University of Minnesota who are trying to find out why the state’s moose are dying at an alarming rate and what, if anything, can be done to save them.

Just 20 years ago, 4,000 moose lived in northwestern Minnesota and 8,000 in the northeast. In 2007, the last time the DNR flew over northwestern Minnesota to count moose, researchers spotted just 18 and estimated the entire population at 100. Meanwhile, the northeast population has dropped to about 2,700.

Researchers have deployed sophisticated technology to discover why. In early 2013, more than 100 adult moose were captured and fitted with Iridium GPS collars, which track location, communicate GPS coordinates to researchers via satellite, and send text messages when an animal stops moving. Researchers also collared 38 moose calves. The goal: to recover within 24 hours any collared animal that dies, in order to get tissue samples and determine exactly how the animal died.

Severud’s interest in wildlife and the outdoors developed while he was growing up in Plymouth, Minnesota. “We lived near a lake, a stream, and woods,” he says. “I was outside a lot.”

At Carleton, “I did a little bit of everything,” says Severud, who majored in biology and got a certificate of advanced study in Japanese. He took advantage of the biology department’s field opportunities to study native prairies in Iowa, mussels in the Boundary Waters, whiptail lizards in Colorado, and the mating habits of millipedes in Costa Rica.

After graduation, he fulfilled his dream to live overseas, teaching English in Japan for two years. Realizing that his heart was set on becoming a wildlife scientist, Severud researched beavers in Voyageurs National Park while he earned a master’s degree in biology at Northern Michigan University. When he heard that Minnesota DNR and University of Minnesota researcher Glenn DelGiudice was looking for a student to help with moose research, he applied for the job—and committed to pursuing a doctorate.

Now Severud spends much of the summer working for DelGiudice, helping to collar moose calves and track down the remains of calves that die. He also helps DNR researchers on a parallel study of adult moose. During the winter, he gathers yellow snow. Yes, that kind of yellow snow. He sets out across northeastern Minnesota by truck or snowmobile until he intercepts a line of moose tracks in the snow. Then he follows the tracks until he finds yellow snow, which he collects and sends to a lab. “By looking at different ratios of amino acids and the composition of the moose urine, we can estimate the nutritional status of the animal,” Severud says.

The statistics are alarming. Of the 111 adults with collars, 26 had died by late January. And 25 of 34 calves had died. While wolves have killed many of the moose, it’s not clear that they are responsible for Minnesota’s shrinking moose numbers, since moose and wolves have coexisted for eons. So far, results don’t point to a single explanation.

Most puzzling, and perhaps most significant, are the sudden deaths of adult moose—moose in the prime of life, with full stomachs, simply falling over with symptoms of extreme malnourishment. Possible causes run the gamut from heat stroke in warmer months, to an increase in parasites such as brainworm (which are transmitted from white-tailed deer), to an abundance of ticks due to warmer winters. Researchers plan to continue collaring and tracking moose this year and next, and analyzing data for a couple years after that.

Many factors probably are working together to cause the decline in Minnesota’s moose population. “It’s a cliché to say that ecology is complex and there’s never going to be a single, simple answer,” says Severud. “This iconic animal is worth saving. Some projections say that eventually the forest will change and Minnesota may no longer be a suitable habitat for moose, but until then, it would be a shame to lose them.”

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