Probing Question: Can groundhogs really predict the arrival of spring?

Jesse Hicks
February 18, 2008
Phil Landmeier

"As I look around me, a bright sky I see, and a shadow beside me...Six more weeks of winter it will be!", predicted Punxsutawney Phil, with the help of human translators, this February 2, Groundhog Day.

According to folk wisdom, if Phil sees his shadow, he'll retreat to his den, and those of us living aboveground will have six more weeks of winter. If he doesn't see his shadow, expect moderate weather and an early spring.

This belief began in Europe, where the Christian celebration of Candlemas incorporated pagan rituals meant to purify and invigorate the spring fields. In Germany, the badger fulfiled the role of furry weatherman; in England and France, bears did the predicting. When the tradition was brought to the New World in the 18th century by the German immigrants known as Pennsylvania Dutch, groundhogs became their stand-ins. (Their buck-toothed mascot, Phil, has made the small town of Punxsutawny, Pennsylvania a popular tourist destination—but the town's Punxsutawney Goundhog Club, founded in 1887, originally had other motives in mind: an annual groundhog hunt and barbeque.)

With all this notoriety, the question remains: Can groundhogs really predict the arrival of warm weather?

Perhaps, but not with rhyming decrees, says Stam Zervanos, professor of biology at Penn State Berks.

Groundhogs, Zervanos explains, have a regular hibernation pattern that begins and ends about the same time every year. "In Pennsylvania they come out, on average, around February 4," he says, "So it's pretty close to Groundhog Day, actually." Male groundhogs emerge to claim territory, clean out their burrows, and prepare for mating, which usually occurs in March.

According to Zervanos, this timing helps ensure that newborn groundhogs survive their first year. Mating too early means limited food in the pre-spring cold; mating too late could prevent young groundhogs from reaching their ideal hibernation weight.

The hibernation and mating pattern varies according to latitude, Zervanos and colleagues discovered. Comparing groundhogs in Maine, Pennsylvania, and South Carolina, they found that, "The colder it is, the longer the hibernation; the warmer it is, the less they hibernate." (In South Carolina the period is so short, Zervanos and his team weren't sure groundhogs there hibernated at all.)

So does this mean Phil and his family have a special understanding of the seasons, enabling them to predict the best time to wake up? Does it explain why Phil's southern cousin, Georgia's General Beauregard Lee, forecasted an early spring?

Not necessarily, Zervanos says. "Now the question is: how much of this difference is genetic, and how much is environmental?" The variance in hibernation patterns could have one of two causes. It could come from genetic differences among the Maine, Pennsylvania, and South Carolina groundhogs. Or it could offer evidence of adaptation: the southerners, living in a warmer climate, would need less hibernation time than their northern counterparts.

Adaptability could help groundhogs survive future climate change. An adaptable groundhog could change with the environment around it, while one with genetically determined hibernation cycles would have a more difficult time. Zervanos hasn't seen much change in Pennsylvania's climate over the past decade, nor in the hibernation patterns of its groundhogs. That data, though, still needs more attention.

The next experiment Zervanos envisions involves removing the animals from their natural habitat to see if they can adapt. "If we took animals from South Carolina and brought them up here, would they fall into Pennsylvania hibernation patterns?" Zervanos asks, "Or would they maintain their southern hibernation patterns?" If the hibernation patterns remain the same irrespective of environment, that would suggest a strong genetic basis. It might also point the way toward, Zervanos explains, identifying the genes that influence hibernation. Such knowledge would help us understand hibernation more generally, from groundhogs to bears. It might help identify mammals in which the hibernation genes are present, but turned off—possibly even humans.

So while Punxsutawney Phil and his fellow furry prognosticators—from New York's Staten Island Chuck to Alberta, Canada's "Prairie Prognosticator," Balzac Billy—can't necessarily predict the coming of spring, they may have much to teach us about surviving the long, cold winter.

Stam Zervanos, Ph.D., is emeritus professor of biology at Penn State Berks. He can be reached at

Last Updated February 18, 2008