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Groundhogs Looking for Love, not Shadow

January 31, 2003

STATE COLLEGE, Pa. (AP) _ Humans believe groundhogs emerge from their dens in early February to look for their shadow _ a predictor of spring.

But the event is more likely the start of a winter courtship, and a prelude to March mating, a Penn State University researcher says.

``During the regular part of the year, the males and females pretty much stay apart. They’re anti-social and, in fact, if they do come across each other they’re sort of aggressive,″ said Stam Zervanos, an associate professor of biology at Penn State’s campus in Reading. ``I think that part of their routine in this part of the year is ... to see which females are available and where they are.″

Observers have long known the early February emergence of groundhogs and other marmots isn’t the end of their hibernation, which comes the following month.

Nevertheless, modern Groundhog Day celebrations evolved from a German superstition that if such an animal sees its shadow Feb. 2 _ the Christian holiday of Candlemas _ then a long winter is in store.

``What’s happening, I’m pretty confident, is that they’re getting together, getting ready for mating that’s going to come later,″ Zervanos said.

During the last four years, Zervanos observed some 30 groundhogs that live on a university-owned farm near Penn State’s Berks-Lehigh Valley College.

Most went into hibernation in early November, then emerged for the first time in early February. Males tended to explore their territory, often visiting the dens of area females, while females tended to stay near the opening of their dens.

After visiting a female, the male might visit another female or return to his den for further hibernation.

That, alone, makes for an interesting finding, said Theresa M. Lee, a professor of psychology and neuroscience at the University of Michigan. She said it’s not uncommon for males of similar species to visit the dens of females, but that the females would remain inside.

``In other species, the females don’t come above ground, so there’s no interaction,″ said Lee, who has studied hibernation and other biological rhythms in rodents. ``That’s quite unique. I have never read that of any other female ground squirrels.″

That might be because groundhogs are somewhat anti-social, Zervanos said. Most other marmots and ground squirrels are more friendly and might not require such a courtship before mating.

Although a male might stay with a female for as long as two days, Zervanos said it appears they do not mate during this period. Groundhogs typically give birth in April after a 30-day gestation period, so it’s unlikely that mating takes place before early March, when the animals emerge for good from hibernation.

It’s also not clear whether groundhogs actually mate with the same partners they visit during February, or whether they choose other partners.

But Zervanos said it’s likely the winter courtship does lead to mating in the spring.

``The male is territorial and he pretty well keeps other males out of his area,″ Zervanos said. ``If a female that he visited in February becomes pregnant in March, it’s highly likely it’s the male that’s in that territory, although we don’t have good evidence of that.″


On the Net:

Penn State Berks-Lehigh Valley College: http://www.bk.psu.edu/

University of Michigan: http://www.umich.edu/

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