Where are the Moose?

Moose apparently have a very narrow temperature window. (Steve Price photo)

Cold-weather animals in decline as temperatures have warmed

It's almost impossible to visit Grand Teton National Park or its gateway city, Jackson Hole, Wyo., without thinking about moose. Road signs warn drivers of moose crossings, guidebooks and pamphlets list favorite moose-watching hotspots, and at least one downtown shop is dedicated entirely to moose-related souvenirs and sweatshirts.


There's a problem, however, which is that northwest Wyoming's moose population is in a rapid decline - not just in Grand Teton but also in the adjoining Bridger-Teton and Shoshone National Forests, which collectively embrace hundreds of thousands of wild, untrammeled acres.

Tragically, the iconic animal's demise may be due to climate change, according to scientists and wildlife biologists who have been monitoring declining moose populations not only in Wyoming but also in Montana, Utah, Minnesota and Michigan for years. The latest Grand Teton-region aerial population surveys tallied only between 800 and 900 total animals, a drop of 30 percent over the past decade. Minnesota's herd fell from approximately 4,000 to less than 100 over a 20-year period.


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"When I came to Jackson in 1995, moose seemed to be everywhere in the park and in the national forest," remembers Wyoming Game & Fish Department Information Specialist Mark Gocke, "but those days are long gone now. Back then, we issued hundreds of moose permits to hunters but now moose tags are issued strictly by lottery, and less than two dozen are available. They're only for bulls, too.

"The casual answer to declining moose populations here for a long time was predation. This ecosystem now includes wolves that have spread south from Yellowstone (as many as 60 animals in five packs); increased grizzly and black bear populations; and mountain lions. Obviously, these four major predators will take down moose, especially calves. The grizzlies may even alter moose feeding patterns, too, since the bears inhabit many of the same areas and forage on the same plants, but historically, moose were declining before the wolves moved down and the grizzlies became so numerous."

What biologists have recognized is that global warming is a monster with spreading tentacles that impact an environment many different ways. Moose, it appears, are being affected at least three different ways, all because it's getting warmer.


First, the animals simply cannot tolerate warm temperatures, but their window of tolerance may be as narrow as three or four degrees, and in the Jackson-Teton area, average spring and summer temperatures have risen this much. Indeed, the past half dozen summers across the entire United States have been the hottest in recorded history. The winters are warmer, too; in northwestern Minnesota, average winters are about 12 degrees warmer now than in the mid-1960s.

Moose are cold-weather animals. They migrated into North America 10,000 years ago from Siberia, but they've never moved much further south than Wyoming in the West or New York/Pennsylvania in the East.

They shed their thick coats in summer but quickly replace them with another equally as heavy. These coats are so thick that snow doesn't melt on them, but rather, adds still another layer of insulation. Thus, warmer summer temperatures can stress moose to the point of over-heating, forcing them into thick cover and shade where temperatures might be a little cooler. Basically, they're resting more and feeding less, with the cumulative effect of leaving them weaker as they enter the harsh winter season.

The warmer temperatures affect plant growth, as well, further contributing to malnutrition issues. Moose need protein and calcium-rich plants in order to survive, and a lot of them. Spring forage is some of the most nutritious of the year, but warmer temperatures translate into a shorter spring growing season so the nutrition is not available for as long. If a cow moose doesn't get enough nutrition, it is less likely to give birth, or even become pregnant, something Gocke and other WG&F biologists have seen through their live-trapping studies.

In the Tetons, a moose's favorite winter foods are the willows, which in extremely cold weather become brittle; moose can easily break them and chew them. If they're not brittle, but instead remain more flexible as the willows do in warmer weather, moose have a far more difficult time breaking them. Although moose do have teeth, they are much less developed than those of other members of the deer family to which moose belong.

Still a third, and potentially more lethal, impact of global warming is the spread of a parasite that can survive and even thrive because of the warmer temperatures. Technically, it's a nematode known as Elaeophora schneideri, but biologists like Gocke call it the "carotid worm" because it invades the moose's blood vessels in the neck and head. Of the 168 moose taken by Wyoming hunters during the 2009 hunting season, nearly half were infected.

"It's one bad character," emphasizes Gocke, "and we're finding more and more moose infected with it. Strangely, it's not fatal in deer, but it can certainly cause death in moose. By invading the blood vessels, it slows or even stops blood flow to vital tissues, ultimately causing lethargy, loss of muscle coordination, blindness, and other forms of brain damage. That, of course, also leads to malnutrition.

"Even if it doesn't kill a moose outright, the worm will certainly leave the animal more susceptible to predation. The real problem is that the warmer the summer temperatures have become, the more tick infestation we've documented. Tick increases have also been well documented Michigan Tech University researches at Isle Royale National Park in Lake Superior where moose have long been present, so it's not unique to this area."

Researchers in Wyoming think the carotid worm is being carried and spread by horseflies. And yes, horseflies do better in warmer, drier conditions. Wyoming's average yearly temperature has risen three degrees in the past 30 years, and each degree equates to about three inches less rainfall annually.

"In truth," concludes Gocke, "there are almost certainly a number of different reasons moose are declining, but I don't think anyone can deny that global warming and its side effects are part of those reasons."

For video of Nicole Jones' moose encounter, click here.

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