What's Caused Half the Minnesota Moose Population to Die Off in Less Than a Decade?

Minnesota's moose have a problem, but biologists aren't so sure what it is yet. What they do know is that about half of the moose population has disappeared within the last decade.

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“If we can really pinpoint the overlying cause, then can we even do anything about it? Or are we really just documenting a species on its way out of our state?" Michelle Carstensen with the Minnesota Department of Natural Resources, who is leading an effort to study why the moose population is dwindling, asked the New York Times.

This year, the DNR estimated 4,350 moose lived within the state. That's about half of what the population was in 2006 when it was more than 8,000.

“Mortality rates of 21 percent among adult moose and 74 percent for calves in the first year of the studies illustrate the complexity of Minnesota’s moose population problem,” Lou Cornicelli, a wildlife research manager for the DNR, said in a statement last month.

But just what is killing the animals off at such a rate is what is perplexing scientists. Those involved in the study are finding out it's likely a variety of factors.

Wildlife biologist Dr. Seth Moore told the New York Times he thinks its root is warmer weather. A shift toward shorter winters and warmer summers could not only weaken the moose immune system but might be contributing to a thriving white-tailed deer population, which carries a brain worm that's fatal to moose.

But he told the newspaper he's “not necessarily convinced that brain worm is the silver bullet that’s killing all of the moose. There are a number of different issues.”

Watch the New York Times' video feature on the Minnesota moose population's plight:

The state DNR's $1.2 million mortality study is tagging moose to collect data that might shed light on why they're dying. This year, 36 adult moose have been tagged and 50 calves are expected to be collared this spring, bringing the grand total to more than 200 being monitored. The study, which the DNR's website described as a first of its kind, has funding to continue into a third year as well, because "data must be collected during the course of multiple years so variations in weather, habitat, physiology and behavior can be factored in."

The tags not only track the animal's location but temperature data. Scientists told the New York Times that after they learn a moose has died, they are able to find it within 24 hours in order to determine the cause of death, which sometimes is still left as unknown.

Last year, Chippewa tribes didn't hunt moose, which they typically rely on for meat, due to the population decline. Mark Johnson, executive director of the Minnesota Deer Hunters Association, told the Minneapolis Star Tribune he thinks they'll do the same thing this year. But the Times reported experts said hunting is not a significant factor in the population decline. Health issues played a role in 50 percent of reported moose deaths in 2013, while predators took up the other half.

Featured image via Shutterstock.