Herd in a Hot Spot

Alaska's Porcupine caribou face an uncertain future as global warming alters their fragile Arctic habitat

  • Lisa W. Drew
  • Apr 01, 2007

FOR THE PAST five years, no one has been able to count the members of the most well-known caribou herd on Earth. Every time scientists have flown over Alaska's Arctic National Wildlife Refuge to photograph the Porcupine herd for a census, something has gone wrong. Most years the researchers have not been able to see the herd--because of clouds, fog or thick wildfire smoke that has blown over the refuge. In 2006 the animals simply did not aggregate in large enough numbers to be counted.

This spring the researchers will try again. If they get lucky this time, a half dozen scientists will spend several days in the fall hunched over piles of 9-inch-by-9-inch images, counting as many as 30,000 caribou in a single print. Among the many people who eagerly await their results are legislators who champion opening the refuge to oil drilling, wildlife conservationists, and Gwich'in Indians who depend on caribou for their sustenance.

But even without the new count, researchers know the herd has not been faring well in recent years. Census results from 1989 to 2001 revealed that its numbers dropped steadily from 178,000 to 123,000 animals. Since then, annual studies of radio-collared cows and their calves suggest the herd size may be as low as 110,000. During the same time, the planet has been warming, and scientists suspect that resulting changes in the herd's habitat have taken a toll on the animals. "What we see is a long-term downward trend that we can't explain by other types of disturbances," says Alaska Department of Fish and Game biologist Steve Arthur.

The warming has been impressive. Global temperatures have risen by 1 degree F over the past 50 years, but in Alaska, they have gone up an average of 3.4 degrees. The biggest shift has been in the winter; in Alaska's Arctic, where the Porcupine caribou roam, winters have warmed by 5.7 degrees.

For animals that live in a very cold place, that might seem to be a good thing. After all, when temperatures drop during the endless Arctic night, and caribou must dig through snow to dine on lichens, the animals use up more energy than they take in. But when the sun returns in late winter--just as the animals have burned up almost all their fat reserves--warming has brought more thaw-and-freeze days in recent years. Snow that starts to thaw can turn to heavy sludge, or it can ice over with a crust. Such conditions can make walking difficult and make it easier for grizzlies, wolves and golden eagles to get at caribou, which often outrun their predators under other circumstances.

Ice also can seal off the caribou's winter food supply of lichen, which may itself become scarce as warming brings about long-term changes in vegetation. Scientists already have documented a northward migration of shrubs, which yield lower-quality forage, into tundra. "We may see an increase in moose habitat and a decrease in caribou habitat," says Arthur. 

The combined impact on caribou is "a pressure" that is probably intensified by a host of others, says ecologist Brad Griffith of the Alaska Cooperative Fish and Wildlife Research Unit. Those pressures are taking a toll on a herd that is finely tuned to specific, unforgiving conditions. "It would only take a 4 percent reduction in the survival of adults to have caused the turnaround from an increase to a decrease in the population," he says.

The warming appears to have a sunny side. Once the snow melts, vegetation is greening up sooner--by as many as 10 to 20 days. In the short Arctic warm season, that's a huge difference. Almost every year, the Porcupine herd migrates from Canada to the Arctic Refuge to calve on the coastal plain, where cottongrass and other plants are plentiful, and wind helps keep the Far North's legendary mosquitoes and other insects at bay. "The earlier it greens up, as evidenced by satellite imagery, the higher the calf survival in summertime," says Griffith. "There's more food for moms, and it puts them out on the coastal plain, where there's more protection from predators and insects."

But there's a catch. Because the plants' lifespans have not changed, they not only green up sooner, they turn brown earlier at the end of summer. If the caribou retreat from this browning vegetation, moving from the coastal plain into greener hills and mountains to the south, they encounter more insects and predators. The mosquitoes are almost unimaginably intense. In one week, they can draw almost half a gallon of blood from a single caribou. For bigger predators, the caribou are a feast. Perhaps even worse, the herd as a whole likely is not as well nourished as it could be for winter. "You give them less to eat and lower-quality food, and things go bad," says Griffith. "The most important thing you can do going into the winter is to go in fat." Without fat reserves, the number of pregnancies is likely to be lower, and the death rates higher.

Elsewhere on the coastal plain, which stretches beyond the refuge across the whole of the state's northern coast, the region's other three caribou herds do not seem to be troubled by warming. From east to west, the Central Arctic herd has been growing for about two decades and now numbers about 31,000; the Teshekpuk herd in the National Petroleum Reserve-Alaska has grown from a few thousand to about 45,000; and the enormous Western Arctic herd, which has been fluctuating, is at about 490,000.

Why the difference? One reason may be simple geography. In the Arctic Refuge, the coastal plain is quite narrow, closely bordered by the foothills and mountains of the Brooks Range. Beyond the refuge, the plain broadens dramatically. "So you have a much wider amount of habitat, and the caribou have more options," says Arthur. The Porcupine herd in the refuge, he adds, "pretty much fills up the available habitat." 

East of Alaska, however, the number of caribou in Canada's Cape Bathurst and Bluenose herds have been plummeting over the past six years. The reasons are unknown, but scientists speculate that oil and gas exploration as well as over-hunting may play roles. They've also noticed low calving rates, cows in poor condition and over-grazing of lichens on parts of the animals' range. As these caribou numbers fall, the region's Inuvialuit subsistence hunters have begun eyeing the Porcupine herd as an alternative food source. Last year, the Gwich'in imposed a voluntary six-week hunting ban to help out the herd, but its effectiveness is not known. If the other herds continue to dwindle, 2007 will bring difficult choices for people whose lifestyles depend on a shrinking supply of caribou.

Ironically, the warming that pressures the Porcupine herd in Alaska results from burning fossil fuels, which have been at the center of a 27-year-old controversy over opening parts of the coastal plain to oil drilling. Now that the herd is clearly stressed even without drilling, there's "cause for concern," as Arthur carefully puts it. "In all likelihood," he adds, "the long-term consequences of climate change are going to be far more significant than the construction of an oil field would be."

Lisa W. Drew teaches journalism at Ithaca College in New York and frequently writes about Alaska.

What's in a Name?

Scientific reports can be deadly dull. So it is with some surprise that this writer looks forward to results of the annual calving survey of the Porcupine herd the way one might look forward to a soap opera. For the report, biologists locate 70-plus radio-collared cows and monitor calving success by flying over the animals in small airplanes. Last year's results led biologist Steve Arthur to conclude that the herd may now number as few as 110,000 caribou. But it's when he notes that "Arnaq, Claudia, Cocoa, Helen and Tundra had calves that survived through late June," and that "Bertha, Catherine, Daphey and Donner were judged to be barren," that his report comes alive for nonscientists. Alas, we may never learn the fate of Blixen, whose transmitter was not working. --Lisa W. Drew

NWF Priorities: The Arctic Refuge and Global Warming

For more than two decades, NWF has been fighting attempts to open up the coastal plain of Alaska's Arctic National Wildlife Refuge to oil and gas development, working both through Congress and with grassroots organizations (see www.nwf.org/arcticrefuge). NWF also is combating the effects of global warming on the refuge and in other wildlife habitats throughout the country. Among other activities, it is backing congressional legislation to reduce greenhouse gases, publishing reports on warming's impact on wildlife and collaborating with its state affiliates on local projects (see www.nwf.org/globalwarming).

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Thousands of Scientists Launch Polar Warming Studies

More than 50,000 researchers from various scientific fields have banded together to launch a broad series of studies on the effects of global warming on polar regions and how those effects will impact human society and natural systems. The scientists announced the International Polar Year in Paris, France, in early March, calling it the biggest polar research project in half a century.

The announcement comes on the heels of a report in February by the Intergovernmental Panel on Climate Change which said that global warming is unquestionably real, very likely caused by human activities and will take centuries to abate.

The polar regions are hit especially hard by global warming. The rate of warming in the Arctic is occurring at nearly twice the rate of the rest of the planet. Average winter temperatures in Alaska and western Canada have risen by as much as 7 degrees F during the past 60 years. Average temperatures in the Antarctic have increased by as much as 4.5 degrees F since the 1940s, among the fastest rates of change in the world. Some climate scientists predict that the Arctic will be ice free during summer within the next century, a change that will have devastating effects on Arctic wildlife and people.

The scientists participating in the International Polar Year will be trying to determine just what those effects will be at both poles. Among other things, they will try to quantify the amount of freshwater entering the sea from melting Antarctic ice sheets; study creatures living on the floor of the Antarctic's Southern Ocean, a region long obscured by thick sheets of ice that are now vanishing; install an Arctic Ocean monitoring system that will provide early-warning data on global warming; study Antarctic lakes and mountains; and research the cultures of the 4 million people living in the Arctic in an attempt to understand how global warming with impact them.

The project is sponsored by the United Nations World Meteorological Organization and the International Council for Science. The $1.5 billion likely to be spent on the project comes mostly from existing research budgets.

The aggressive thrust of the project fits a comment made by Prince Albert II of Monaco at the launch. Global warming, he said, is "the most important challenge we face in this century. The hour is no longer for skepticism. It is time to act, and act urgently."--Roger Di Silvestro

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Canadian Tundra Shrinking

While scientists have long predicted that the area of the world's tundra will decrease as global climate warms, results of a new study suggest that the habitat--home to caribou and other wildlife--may be disappearing even more rapidly than expected.

Using tree ring data to date the establishment and death of spruce trees in southwestern Yukon, University of Alberta biologist Ryan Danby and his colleagues reconstructed changes in the location and density of treeline forests over the past three centuries. At all of their study sites, the scientists discovered rapid changes in vegetation during the early to mid-twentieth century. On some warm, south-facing slopes, tree line rose as much as 278 feet in elevation, overtaking what historically had been frozen tundra. The researchers published their results last month in the Journal of Ecology.

"The conventional thinking on tree line dynamics has been that advances are very slow because conditions are so harsh at these high latitudes and altitudes," says Danby. "But our data indicate that there was an upslope surge of trees in response to warmer temperatures. It's like the tree line waited until conditions were just right, and then it decided to get up and run, not just walk."--Laura Tangley

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