Climate change likely to affect diet of adaptable bears

Yellowstone grizzlies need a lot of fuel.

At its hungriest, one might consume 20,000 calories a day.

But for the 500 or so grizzlies that live in and around Yellowstone National Park, the Earth's warming climate may change what's on the menu.

All four of the most important food groups for the bears -- whitebark pine nuts, moths, cutthroat trout and winter-killed elk and bison -- could potentially be affected by global warming. The difficulty, though, is predicting how.

That will be one of the central questions looking forward as Yellowstone grizzly bears today are removed from the endangered-species list.

Federal bear biologists who proposed delisting say grizzlies are highly adaptable and that managers will keep an eye on the bears and do what they can to make sure they can survive.

Climate change or no, though, grizzlies have found ways to survive again and again in unstable environments, bear officials said. Their omnivorous tastes run from bugs and roots to meat, garbage and nearly everything in between.

"You're talking about one of the ultimate generalist species. It eats everything," said Chris Servheen, grizzly recovery coordinator for the U.S. Fish and Wildlife Service.

Others, though, are worried the threat isn't being taken seriously enough and that it's premature to remove federal protections that have been in place since 1975.

Yellowstone is particularly vulnerable to the effects of climate change, and threats to grizzlies' food sources make the decision to delist "highly questionable," said Stephen Saunders, president of the Rocky Mountain Climate Organization, a Colorado-based coalition of nonprofits, businesses and local governments.

"It's one of all too many examples of how our federal government hasn't taken climate change as seriously as it needs to be taken," said Saunders, whose group helped produce a report last summer about climate change and national parks in the West.

Since 1915, the average minimum winter temperature in the Yellowstone area has increased by about 6 degrees, said Jeffrey Hicke, an assistant professor of geography at the University of Idaho.

The Intergovernmental Panel on Climate Change has said in separate reports this year that the world's climate will continue to heat up in the coming years.

"We know there is an increase in temperature in the atmosphere, there's no doubt about that," Servheen said. "We expect there will be some effects."

The extent, though, "is difficult to foresee with any level of confidence," said a federal document outlining plans to delist the Yellowstone bears.

That should prompt the federal government to go slow on delisting and give bears more room to roam, some environmental groups have said.

"Like the polar bear, the grizzly is facing an increasingly uncertain future in a world of shrinking habitat as a result of warming temperatures," said Louisa Willcox, of the Natural Resources Defense Council.

Pines in peril

One of the biggest worries is what climate change might do to a tiny, protein-packed nut that grizzlies love.

The nuts grow on the branches of whitebark pines, a gnarled-looking tree that grows at high elevations.

The trees typically don't produce seeds every year. But when there's a good crop, birds and squirrels cache them in the ground and grizzlies snatch them up for a high-fat snack.

In those good years, female grizzlies produce more cubs per litter and reproduce more often. Bears also stay in the mountains where they're less likely to come in conflict with people and eventually get killed.

But the trees have come under attack in recent years -- first by a non-native fungus called blister rust and, more recently, by millions of minuscule, ravenous bark beetles.

It's estimated that about 25 percent of whitebark pines in the Yellowstone area are infected with blister rust, which isn't always lethal but can reduce seed production. On top of that, more than a half-million whitebarks have been killed in Yellowstone and on surrounding national forests during an outbreak of native pine beetles, according to a 2005 estimate.

That one-two punch is raising doubts among some about the future of whitebark pines and the alpine ecosystems they anchor.

"We don't think that whitebark has a good fighting chance between this exotic disease and the mountain pine beetles," said Diana Tomback, a biology professor at the University of Colorado at Denver and director of the Whitebark Pine Ecosystem Foundation.

Several scientists have tied the threat to climate change.

"It may not be able to adapt to changing climates," said a U.S. Forest Service report from last summer called "Whitebark Pine in Peril."

Jesse Logan, who recently retired as a U.S. Forest Service entomologist, has linked the beetles' activity in high-elevation whitebark stands to milder temperatures that not only allow beetles to survive winters but also to move to higher elevations.

"We are witnessing the catastrophic collapse of high-mountain ecosystems as a result of how people are changing the climate, and grizzly bears could end up paying the price," Logan wrote in an essay last year.

There have been previous large-scale outbreaks of the tree-killing bugs that appear to have ended when temperatures cooled, said Idaho's Hicke.

"But what seems to be different today and continuing into the next 100 years is the temperature is going to stay warm," Hicke said.

The effects on blister rust are less clear, Tomback said. It could be that warmer temperatures help the spread of its spores, she said. Judging by what blister rust has done elsewhere, she said that the fungus is likely to take a larger toll on whitebark pines.

"We know that blister rust is going to get worse in the greater Yellowstone area," said Tomback, who advocates for restoration of whitebark pines. "It's a repeated pattern we've seen everywhere."

Servheen said the hardest hit areas are likely to be in the western part of the Yellowstone ecosystem while most bears that use the whitebark nuts are in the eastern portion.

"This is not a food that needs to be there every year for bears to survive," Servheen said. "The key issue is not that change in pine nut availability. The key issue is how they're going to respond to that change."

Other foods

The long-term effect of climate on other key grizzly foods is also unclear.

Milder conditions would allow more elk and bison to survive winter to provide a food base for grizzlies, Servheen said.

But those warmer temperatures could also mean reduce the number winter-killed elk and bison that grizzlies rely on they emerge from hibernation.

Wolves, though, may buffer that effect, according to a study by University of California, Berkeley study. Researchers there said Yellowstone wolves kill elk no matter the winter conditions, providing carcasses for other animals such as ravens, magpies and grizzly bears.

Yellowstone cutthroat trout, another springtime food for bears, might also change.

Milder conditions in the winter could push spring runoff 30 to 40 days earlier in Yellowstone, which could require bears to change when they visit spawning streams, federal officials said.

That trout supply has already been severely diminished in recent years because of non-native lake trout, whirling disease and the ongoing drought that has disconnected streams from Yellowstone Lake.

But a 2005 study indicated the number of bears that eat the trout varied from 15 to 33 between 1997 and 2000, indicating that it wasn't a major food source for the overall population. Many of those were also males, which aren't considered as important to the population as females.

There's also speculation about the fate of army cutworm moths, perhaps the richest food in the greater Yellowstone area.

Just before grizzlies enter hibernation, nearly half of the population packs on the pounds by stuffing themselves with moths, which migrate to the cool shade of Rocky Mountain slopes each summer.

One study indicated a 250-pound grizzly could eat 40,000 moths per day.

Some say it's possible that a warmer climate could wipe out high-elevation plants where they feed on flower nectar at night. Others say lower elevation plants might be a viable alternative.

An ability to adapt

John Varley, who recently retired as Yellowstone's lead scientist, said that one way or another, grizzly bears will find something to eat and survive as long as they have enough room.

There's no doubt that the effects of climate change will ripple through Yellowstone, he said. It might be that grizzlies become smaller over time as a result of effects on food.

"We know there's going to be a change," Varley said. "But these grizzly bears have an ability to adapt that we're only beginning to understand."

Servheen said 60 to 80 grizzlies in the Yellowstone system have radio collars, allowing wildlife managers to keep a close eye on how they're doing.

After delisting, nearly $4 million a year will be spent to monitoring and management. Changes can be made to help grizzlies overcome food shortages and if bears run into too much trouble they can be placed back on the endangered species list, he said.

"This is a managed population," Servheen said. "Delisting doesn't mean we walk away from them and say, 'Good luck, hope you're there in 100 years."'