Mysterious climate stress stalks north woods moose population

MINNEAPOLIS -- Make room, polar bears. The looming catastrophe involving large species declines caused by climate change has a new poster child: the North American moose.

Researchers from the United States and Canada say the iconic antlered mammals -- whose southern range extends from New England to the northern Great Lakes to portions of the Rocky Mountain West -- could be gone from parts of the Lower 48 by midcentury. Rapid population declines are already being seen in northern Minnesota and in Isle Royale National Park on Michigan's Upper Peninsula.

Surveys in both states, as well as in portions of North Dakota, Manitoba and Ontario, indicate that hundreds of adult moose are dying off every year due to a mysterious series of circumstances that cannot be explained by the normal burdens of disease, predation and human hunting.

Rather, scientists believe that moose in the Lower 48 and particularly those in the upper Great Lakes region may be succumbing to stresses associated with a warming climate -- which, when combined with other causes of mortality, is devastating herds that used to be a fixture of the north woods.

In Minnesota, the state's two largest herds have declined from a combined 14,000 individuals in the 1980s to roughly 7,600 today, according to the state's Department of Natural Resources. The smaller of the two populations, in the northwest corner of the state, was all but wiped out last year, when DNR surveyors counted only 100 individuals, down from roughly 4,000 a decade before.

"They just dropped off the face of the earth," said Mark Lenarz, a DNR research biologist who as tracked the state's moose die-off. While moose hunting is not believed to be a factor in the animals' long-term viability, Minnesota is considering banning it temporarily, at least until more information is known. State regulators this year issued 246 licenses to moose hunters, and fewer than 150 bulls were shot, including 30 that were taken by members of the Ojibwe tribe.

'Profound trouble' in changing climate

The same pattern is occurring in parts of Michigan's Upper Peninsula, where moose in Isle Royale National Park have declined by nearly 75 percent in just 13 years, from roughly 2,400 animals in 1995 to 650 in the latest surveys released earlier this year. Scientists who have studied moose populations on the island for decades say the crash is due at least in part to changing climate conditions that make moose more vulnerable to a range of threats, including parasites, viruses and even starvation.


John Vucetich -- a wildlife biologist at Michigan Technological University and co-director of the Isle Royale Wolf/Moose Study, the longest-running predator-prey research project in the United States -- said a changing climate portends "profound trouble" for the moose, which have inhabited the 210-square-mile Lake Superior island for just over a century, probably after swimming from Canada or Minnesota's shorelines.

"For the last 20 years, on Isle Royale, the moose have been up and down a lot due to a variety of factors, some of them perfectly normal," Vucetich said. "However, for about the last seven or eight years, moose have been on a much steadier decline, and that is raising a lot more suspicions," including suspicions about climate change.

Perhaps the most critical component to moose health, scientists say, is temperature. The animals are acclimated to cold climates, and even modest rises in summertime temperatures can have serious implications for their mobility, feeding habits and other behaviors.

And while the exact reasons for moose mortality will remain varied, Vucetich said the climate trend foretells a few undisputable truths. "Whether it's Isle Royale, Minnesota or North Dakota, what's going to happen is these moose are going to disappear as temperatures increase," he said. "They will die off at a quicker rate and reproduce at a slower rate until eventually they are all gone."

Moose can't sweat this out

Unlike many domesticated mammals, moose are not physiologically equipped to sweat. Rather, they cool themselves by increasing their respiration rates. "At a certain temperature, they'll actually start to pant just like a black lab," said Lenarz. But unlike dogs, moose begin to experience physiological stress at much lower temperatures. "When it gets into the high 50s, maybe 60 degrees Fahrenheit, they have to increase their respiration to cool off," he said.

As summertime temperatures in the northern regions continue to tick upward on a warming climate, moose have become increasingly weak and lethargic, scientists say, increasing their vulnerability to a variety of threats, including parasites, disease and predation by wolves. That lethargy, combined with other adaptive behaviors aimed at cooling themselves -- such as immersing themselves in ponds for hours at a time -- also inhibit other critical summertime activities, such as eating.

Moose consume massive quantities of vegetation in the summer months to build fat stores that are burned off during the long winters. But lethargic and sickly moose are less likely to put on sufficient winter weight, resulting in growing starvation rates among otherwise healthy animals. "When you're ending up getting prime-aged animals die, that's when it really is kind of a wake-up call that something is abnormal," Lenarz said.

On Isle Royale, scientists have noted that in addition to the direct stress associated with warmer temperatures, moose are becoming more vulnerable to infestation by winter ticks that are flourishing under generally milder conditions. An adult moose can amass as many as 50,000 of the blood-sucking ticks in a season, leaving the animal severely weakened and in some cases dead. Severe tick infestation also can prompt moose to rub their bodies against large trees, removing large patches of fur that otherwise provide protection against winter cold.

While many questions remain about the relationship between climate change and moose mortality, scientists are increasingly confident that under current climate conditions, the animals will be extirpated from their historic southern range in the Lower 48 states, particularly in the Midwest and possibly in New England. Moose in the Rocky Mountain ranges of the West, meanwhile, may migrate to higher elevations to maintain cooler temperatures.

No more moose, no more gray wolves

Such decline could have serious ecological implications for places like Isle Royale, where for decades moose and gray wolves have lived in ecological balance for 50 years. But all of that could change as moose populations disappear, leaving the island's roughly two dozen wolves without a ready source of food. In fact, Vucetich said, wolves on the island are much more likely to face extinction, given their relatively small numbers and the fact that moose meat accounts for 90 percent of their diet. In neighboring Minnesota and other parts of Michigan's Upper Peninsula, wolves would likely fare better because they have other food sources, including abundant white-tailed deer.

Even so, experts say, the loss of the moose and wolves from parts of their native habitat reflects one of the greatest threats associated with climate change -- that as ecological systems shift, even the hardiest species -- in some cases those with tremendous symbolic value -- will be lost, perhaps forever.

"Moose are creatures of the North Country, and we're living with them about as far south as we see them in the world. As it gets warmer, they're not going to be there anymore," said Vucetich. "It would be tragic, among other reasons because they're beautiful animals."

Click here for more information on the Isle Royale Wolf/Moose Study.

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