Mysterious Moose Die-Offs Could be Linked to Global Warming

A male moose. Photo by PL Przemek via Wikimedia Commons.

One of North America’s largest land mammals is in trouble, and so far, scientists haven’t been able to pinpoint the culprit.  Moose have recently experienced alarming declines across the continent. For example, in Minnesota, the northwestern population of moose has declined from 4000 to less than 1000. Predation, parasites, hunting and heat stress may all be contributing to the moose die-offs across the United States. But some scientists are fingering another culprit – climate change – which affects nearly all of those factors by shortening winter seasons and driving up temperatures. 

However, the link between moose mortality and climate change is a difficult one to prove.  Wildlife biologist Mike Schrage told Minnesota Public Radio:

I do think global warming is having an impact on our moose.  I think it gets complicated between climate change and a dead moose. Because I don’t think I’m ever going to walk up on a moose carcass and be able to say, oh, it died of climate change.  I think there’s a lot that happens in between.”

That said, there has been a notable rise in temperatures across moose habitats. Over the last 40 years in Minnesota, the average winter temperature has risen 11 degrees Fahrenheit, which is undoubtedly bad for the moose. 

In New Hampshire, the state population of moose has dropped from 7000 to just 4,600.  Ticks, which seem to be the leading factor contributing to moose deaths, have been thriving due to the shorter winters. Up to 150,000 ticks can swarm a single moose.  The New York Times reports:

The winter tick problem in New Hampshire is particularly vexing.  The animal can loose so much blood they can become anemic.  Worse, the ticks drive the moose crazy; they constantly scratch, tearing off large patches of hair. 

Some moose lose so much hair they look pale, even spectral; some people call them “ghost moose.”  When it rains in the spring, the moose, deprived of their warm coats, then become hypothermic. 

Kristine Rines, a wildlife biologist at the New Hampshire Fish and Game Department, told the Washington Post:

“It’s a pretty tough way to go.  There’s no question that climate plays a huge part in this.  If we had winters that lasted as long as they used to, we might not be having this conversation.”

A recent study also says that warming climate has also allowed pine bark beetles to thrive in the Cariboo Mountains of British Columbia, killing the forests and leaving moose exposed to hunting and animal predators. 

The population decline spells trouble not only for the moose, but also for the entire ecosystem. Moose provide nourishment for large carnivores, such as bears, and they help create habitats for nesting birds and rabbits by eating back shrubs and bushes. Moose decline may also hurt the economy in New Hampshire, where moose-watching brings in $115 million a year. 

However, establishing a correlation between climate change and moose die-off, if there even is one, will require further research into moose mortality. 

The Minnesota Department of Natural Resources (DNR)started a $1.2 million study in January monitoring Minnesota moose. The animals were fitted with GPS collars and made to swallow a tiny transmitter, which, from the stomach, measures body temperature and heartbeat. This monitoring technology allows scientists to be notified immediately, via text message, if a moose dies.  The scientists then use the GPS coordinates to track down the remains and quickly conduct a necropsy.  Moose cadavers decompose quickly because of high body-fat levels, making a necropsy after 24 hours almost useless. However, the study is still in its beginning stages.

The DNR wrote:

“As of yet, there isn’t enough data to answer with certainty why Minnesota’s moose population has dropped 52 percent since 2010.  And it’s far too early in the study for researchers to even consider possible solutions that might slow the precipitous decline. Science is a slow process.”

State officials have suspended Minnesota’s moose-hunting season this year, which will hopefully buy the time needed to solve this mystery. 


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