Global warming is marmot wake-up call

If Punxsutawney Phil lived in Colorado instead of Pennsylvania, the groundhog weather predictor might need to forecast an early spring every year.

Yellow-bellied marmots (also known as groundhogs or woodchucks) are now emerging from their 8-to-9-month hibernations 38 days earlier than they did 23 years ago, according to a long-term study by scientists working at the Rocky Mountain Biological Laboratory in Crested Butte, Colo.

Global warming may be cutting short the marmots’ long winter naps, says David W. Inouye, a biologist at the University of Maryland, College Park. The warmer the temperatures, the earlier the marmots’ appearance.

On average, April in the Rockies has gotten progressively warmer since the researchers began measuring in 1976. They say the month’s average is 1.4ºC higher now.

This temperature change isn’t enough to be statistically significant, but it seems to have relevance for the marmots, says botanist Ken Thompson of the University of Sheffield in England. “Marmots know nothing about statistics. They only know what’s happening around them,” he says.

Other studies have shown that birds have nested earlier in response to climate change (SN: 6/12/99, p. 383).

Unlike marmots, Colorado’s chipmunks and ground squirrels seem to be sleeping in. Inouye and his colleagues found that least chipmunks come out of hibernation 12 days later and golden-mantled ground squirrels, 27 days later than they did in 1974.

The chipmunks and ground squirrels use a different hibernation alarm clock than marmots do, Inouye reported this month to a joint meeting in Orlando, Fla., of the Ecological Society of America and the British Ecological Society. The marmot study appeared in the Feb. 15 Proceedings of the National Academy Of Sciences.

While marmots measure only air temperature, chipmunks and ground squirrels also gauge the thickness of snow blanketing the ground, Inouye says. The animals rouse themselves periodically to eat and see if spring has arrived. When there’s snow on the ground, they tend to hit the snooze button and go back to sleep, he says. The snow depth taken annually on April 30 at the research site, a measurement that predicts when the animals emerge, has increased by 57 centimeters since 1976, the researchers say.

Longer or shorter hibernating times may make life difficult for the rodents, Inouye says. Marmots must wait longer for the snow to melt after they’ve emerged, while ground squirrels and chipmunks need to store more food for their longer hibernations.

Thompson says marmots are survivors and will probably adapt to new conditions. “They’re not stupid,” he says, “and even if they were, natural selection would soon correct them.” This type of long-term study is valuable for interpreting how climate change affects animals, Inouye says.

“One can only get this sort of information from these long-term [studies],” agrees Terence P. Dawson, an ecologist from the University of Oxford in England.