PHILADELPHIA - Why groundhogs bother to get up at all today - on Groundhog Day - has, until now, stood as one of those insoluble mysteries of science.
Year after year, they rouse from a deep hibernation at this time of winter, still a month away from mating season and with absolutely nothing around for them to eat.
Scientists, being naturally skeptical, don't think they do it just to help humans determine when spring is coming.
In fact, new research indicates groundhogs emerge from their holes, like so many single people on a Friday night, to check out the dating scene.
"What's so amazing is the timing," said Stam Zervanos, an evolutionary biologist who has been watching groundhogs for the past four years on Penn State University's Berks-Lehigh Valley campus, near Reading (about 200 miles from Punxsutawney, home of today's official arbiter of early spring). It's dark and they're all alone, but the creatures seem to know just when to get up, he said.
When groundhogs hibernate, they lower their metabolic rates, and their body temperatures drop to about 45 degrees. The length of their hibernation varies depending on where they live; in Pennsylvania, they doze off in early November, wake up in late January or early February, then get up for good at the end of February.
For the past four years, Zervanos monitored 15 groundhogs. He watched them with hidden cameras and monitored their movements with miniature transmitters implanted under their skin.
He found that groundhogs start daily trips out of their burrows in late January and continue into early February. Then they go back to sleep for several more weeks.
He's still puzzling over the nature of the groundhog's internal alarm clock, but he does have a theory for why they get up early.
What they're doing, he suspects, is something like groundhog dating.
Both male and female groundhogs get out and look around, and if a male sees a female in his territory, he goes to her burrow and sometimes stays for a day or two before retreating to his own burrow or off to visit another female.
What do they do down there?
"I wish I knew," said Zervanos.
They're probably not mating. Mating in midwinter would produce offspring with no chance for survival, so Zervanos suspects it's something other than that.
Timing is crucial for survival of the young, said Zervanos. Mate too early, and the baby groundhogs will die for lack of food. Too late, and they can't put on enough fat to survive hibernation during the next winter. Only by pairing up during the first two weeks in March can groundhogs produce offspring with any hope for the typical 3- to 4-year groundhog life span. The gestation period for groundhogs is 31 to 33 days.
The early February forays, he said, might be a time for them to "get acquainted." Males need to find which females live in their territory, and they might need to establish that territory by chasing away rivals.
Then, when the actual mating season begins, around March 1, "they know exactly where to go," Zervanos said. No confusion about who will mate with whom.
Because the males do all the scouting around, they tend to get eaten by hungry foxes and coyotes. The females rarely stray far from their own burrows, so they end up outnumbering the males by a significant ratio, allowing the males that survive to find several mates.
For Punxsutawney Phil, the fabled Pennsylvania prognosticator, this is good news and bad news. When he is brought out into the limelight each Feb. 2 and held up for the television cameras, Phil is missing his chance to meet the new girls on the block. However, he is also missing his opportunity to be a coyote's dinner.
(Today, Phil's audience will include Pennsylvania Gov. Ed Rendell, the first governor to attend a groundhog event in Punxsutawney since Gov. Edwin S. Stuart went to a Groundhog Banquet picnic there in the summer of 1909.)
Zervanos said that studying the groundhog helps broaden the understanding of other closely related animals, collectively called marmots. Some marmots are severely endangered, he said, including a group in Vancouver, British Columbia, that is down to about 30 individuals.
There is one other reason that groundhogs might want to go outside on a cold, early February morning, Zervanos said. Though they don't eat or drink while hibernating, groundhogs do burn much of their own fat, which can produce metabolic waste, he said:
"So they may be getting up to go to the bathroom."