Urban Jungle

January 29, 2013

Groundhogs and global warming

When Groundhog Day arrives Saturday, don't waste much time expecting to see your local groundhog. It's too early. Normal emergence in the Washington area is late February or early March — but a steadily warming world might change that.

In some parts of the country, groundhogs and other marmots have been leaving their burrows earlier than usual. By 2010, groundhogs in Maine were emerging about 17 days sooner than in 1998, according to marmot expert Kenneth Armitage, a professor emeritus of behavioral ecology at the University of Kansas.

When a groundhog, also known as a woodchuck, pops its head out of his burrow, he's focused on the temperature of the air, not the angle of his shadow. If the marmot senses it's too cold to start the season, he will retreat to his hibernaculum and slip back into torpor.

Groundhogs drift in and out of torpor, a state of hibernation, all winter long, sacrificing some of their stored fat so that they can wake up every week or so, which probably helps reduce some of the bodily stresses that torpor exacts on the marmot. A groundhog in torpor inhales only once every five minutes, its temperature has fallen from 96 to 47 degrees and its heartbeat has gone down from 100 beats a minute to five. At least a quarter of groundhog deaths occur during torpor.

A male waking up for good in late winter will have lost almost a third of his body weight. He might look emaciated, but he's fired up to breed and visits the burrows of several females to arouse them with his woodchuck ardor.

An earlier exit would leave more fat on him, giving the groundhog a survival edge. Breeding sooner would also be less stressful for females, provided that plenty of grass, clover and garden vegetables are available. An earlier season would allow pups more time to mature and fatten up for next winter.

But a warmer world isn't necessarily a rosier one for other marmot species. Climate change can affect snowmelt in mountain habitats, which "increases survival and reproduction in the short term," Armitage writes in a yet-to-be-published book. "But if early snowmelt is associated with less moisture during the active season and drier vegetation during the summer, higher mortality and decreased reproduction will most likely follow."

Sources: Kenneth Armitage, University of Kansas; Elizabeth Watson, University of Illinois; Proceedings of the National Academy of Sciences; Physiological and Biochemical Zoology