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Feeling the Heat: How Global Warming is Affecting Wildlife Habitats

Feeling the Heat: How Global Warming is Affecting Wildlife Habitats

Illustration by Mike O'Brien

Something's going on with Minnesota's moose. What was once a thriving and healthy herd has virtually crashed, plummeting from 9,000 animals in 2006 to 4,350 this spring. Moose numbers are falling in New England, as well. New Hampshire has seen a 43 percent decline since the 1990s. Even Maine is experiencing a slide in its moose herd.

Things are so bad in Minnesota, the state suspended its annual hunt indefinitely and is funding a five-year, $1.2 million study to find some answers.

No one knows for sure yet, but a growing number of experts point to a common theme.

"We are seeing a number of factors related to shorter, warmer winters, like an increase in the abundance of winter ticks and a higher rate of liver flukes and brain worm," says Minnesota Department of Natural Resources Wildlife Health Program Supervisor Dr. Michelle Carstensen. "Winter ticks are able to survive warmer winters after they drop off, so the more that survive one winter, the more there are the next winter. We've seen moose with hundreds of thousands of ticks on them. The moose basically bleed to death."

Carstensen can't say if climate change is the culprit, but a growing number of wildlife scientists have come to the same conclusion. The Earth is getting warmer, and it's having a direct impact on wildlife and the places birds and animals live.

University of Colorado-Boulder Assistant Ecology Professor Dr. Christy McCain examined 140 peer-reviewed studies that looked at the impact of climate change on 73 mammal species. Some are shifting their ranges northward or toward higher elevations, other populations are declining and average migration dates for some species are different. Those changes may be subtle and virtually unnoticeable to the casual observer, but some are obvious. Armadillos and raccoons are showing up farther north. So are opossums.

"Some of the studies were conclusive. The changes could only be a result of warmer temperatures. Other changes could not be tied only to climate change," says McCain. "Anthropegenic changes to populations like habitat loss, for example, may be playing a role in the decline of some species."

She adds that large mammals show the strongest negative response to warmer temperatures. Researchers with the University of Alberta found a correlation between a worldwide decline in caribou and reindeer numbers and warming temperatures. New research in Wyoming found that long-term weather patterns consistent with climate change are shifting migration activity in moose and mule deer.

Another study found that warming trends are leading to significantly lower elk calf-to-cow ratios. Wyoming Cooperative Fish and Wildlife Research Unit leader Dr. Matt Kauffman says there is a distinct correlation between early, rapid green-up and low calf recruitment for both elk and moose. He examined weather patterns and cow-calf ratios in a migratory elk herd in northwestern Wyoming over the last 20 years.

"Warmer winters lead to a more rapid green-up and a shorter growing season. As a result, food sources lose their nutritional value faster," he explains. "Cows have lower fat reserves in the fall and are less likely to breed. We saw lower pregnancy rates following warmer, drier winters, which are occurring more frequently."

Kauffman says mule deer and moose seem capable of adapting to the changing habitat by timing their migrations with seasonal green-up. However, he adds long-term drought is taking a toll on both species. Mule deer numbers have declined throughout much of the West. So have moose populations.


"We [he and his fellow researchers] are comfortable making an inference that the recent trends in weather patterns are connected to climate change. We are staying clear of what's causing long-term drought, but the changes we are seeing are what we would expect with climate change," he says.

It isn't just big game. A new study is examining the decline of scaled quail in the Southwest and will examine the impact of climate factors on nest success and overall populations. Like bobwhites, scaled quail are largely disappearing from their historic ranges. The decline of bobwhites is widely linked to habitat loss, but that doesn't seem to be the case with scaled quail.

Their numbers are falling in regions where there is no grazing or widespread development. Habitat loss is also a factor in the decline of mountain quail, which are elevation-specific. However, a California study found the birds have shifted their range more than 370 feet upslope in the last 26 years, a shift that coincides with average temperature increases.

Landscapes are changing, too, according to a number of studies. One found that dominant plant species in California's Santa Rosa Mountains crept upward by nearly 200 feet in elevation since 1977. The line separating hardwoods and conifers is inching up the slopes of Vermont's Green Mountains, as well.

One of the most obvious changes to habitat is taking place in Colorado and other Western states. Entire mountain ranges that were once covered in vibrant green pines are now littered with the skeletal remains of those trees. At least 4.5 million acres of lodgepole pine and spruce forest have been killed by pine bark beetles in Colorado alone. Overall, an estimated 100,000 square miles of timber have been wiped out from New Mexico into Canada.

Some experts agree increased fire suppression has led to an increase in pine beetles, but a number of studies have pointed to the combination of warmer temperatures and drought, which stresses trees. The beetles now survive more winters and they reproduce at a faster rate. They are also living at higher elevations and in more northern latitudes. The insects are a native species and have always played a role in the natural cycle of forests, but the extent of damage is unprecedented.

The altered habitat is having a ripple effect. Wyoming Game and Fish Senior Wildlife Biologist Tony Mong is in the midst of a five-year study that is examining the impact of dying lodgepole forests on elk and elk hunters in the Medicine Bow National Forest. He wants to know if the affected areas are creating more difficult hunting opportunities, if elk are more vulnerable to hunters, and if the changes are impacting elk migrations, among other things.

"Elk need those thicker pine forests for cover from predation, including hunters," says Mong. "On the other hand, the additional grass coverage in the new openings will produce more forage for elk, so it may in some ways benefit elk."

Mong says the altered landscape could actually benefit mule deer, as well. The new growth that is thriving on the forest floor among the dead pines is loaded with high-quality deer forage.

Warmer winters are also allowing whitetails to expand their range northward. While that may provide more hunting opportunities, the increase in deer has been linked to the decrease in Minnesota moose. Whitetails harbor brain worms, which are deadly to moose.

When big-game populations decline, so do hunting opportunities. Maine cut the number of moose tags from about 4,000 last year to 3,095 this year. New Hampshire will offer just 124 moose permits this year. A decade ago they sold 675.

In the meantime, more research is being conducted on the impact of warming temperatures on wildlife and the places they live. Although skepticism continues to run deep throughout the country, Kauffman says most wildlife biologists agree things are changing.

"We've moved way beyond the debate of 'if'," he says. "We now want to know the long-term impact, and what, if anything, we can do about it."

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