Every February 2, news crews from around the country crowd into Punxsutawney, Pennsylvania, for the annual appearance of Punxsutawney Phil, the world's most famous groundhog.

Why the hullabaloo? Here's the theory: If Phil sees his shadow, winter will last six more weeks. If he doesn't see his shadow, winter is over and spring is on the way.

Not too shabby ... for a rodent. (News flash: Phil did not see his shadow this morning--spring is on the way!)

But wait a second. Let's take a closer look. What makes Phil see his shadow? Sunshine, of course. So why can't we just look out the window and see if it's sunny? Wouldn't that allow us to cut out the go-between? Or do groundhogs have some special weather-predicting prowess?

Nope, sorry. The whole thing is nothing more than a tourist attraction. I hate to break it to you, but Phil comes from a zoo. His agent apparently worked out this cushy Groundhog Day gig--one annual appearance in exchange for year-round maintenance and a signing bonus.

So what's really going on? Well, even though groundhogs may not have any special powers, there is still amazing talent on display here. I'll tell you what it is: hibernation. When groundhogs come out of their burrows they're not doing it for our benefit, they're checking to see if it's time to stop hibernating.

"Hibernation," you say. "You mean like how bears sleep through the winter?"

Uh-oh. Sounds like I've got a few more bubbles to burst.

Ah, hibernation!
I have often envied hibernating animals. I used to think of joining them and pictured myself in a cozy den, with socks toasting by the fire, a stash of videos, a pile of good books, and the delicious rhythm of going to bed early, sleeping late, and taking long naps.

The thing is, hibernation is not like sleeping; it's a lot more like being dead. When you fall asleep, your body slows down and your temperature drops a little, but everything stays within the normal zone. When animals hibernate, their systems come close to shutting down.

Take the groundhog, for example. During hibernation the groundhog breathes about once every four minutes, its heart beats four times a minute, and its body temperature drops from a normal of about 99 degrees Fahrenheit (about the same as ours) to about 36 degrees--just above freezing. Actually, since the groundhog hibernates about eight months of the year, 99 degrees might be called its abnormal temperature. Nearly frozen and nearly dead is a groundhog's normal state!

X-treme hibernation
Think that's impressive? You ain't seen nothin' yet.

When bats hibernate, their breathing slows down so much it can only be detected with instruments. They feel cold to the touch, and drops of dew form on them. Because they hibernate above ground, people have seen them in this state. No wonder bats are associated with stories of "the undead."

Some animals go even further. The Arctic ground squirrel hibernates at a body temperature below freezing--and yet doesn't freeze. The ground squirrel is able to do this because before hibernation it goes through a sort of internal purification that gets rid of any particle that might seed the freezing process. Liquids require such a particle (sometimes called a nucleus) in order to freeze. By purging itself the squirrel avoids becoming an ice cube, even if the temperature drops below freezing.

Want even more? Try this on for size: There is a type of Alaskan beetle called the carabid that creates its own internal antifreeze (known as a glycoprotein, if you're interested). This beetle hibernates in tree stumps when the temperature drops to 40 degrees below freezing. In the spring it wakes up, and it's fine.

Why do animals hibernate? Well, think about it. It's cold, there's nothing to eat, and mating season is months away. They might as well be almost dead. The great thing about being almost dead is you need almost no food. Some creatures go into hibernation whenever food gets scarce, regardless of what season it is. And some animals that live in hot places, like deserts, go into estivation, which is like hibernation: The body systems all but shut down. Estivation is more about conserving water than energy, but it's the same strategy.

Groundhogs, bears, and daily torpor
Everybody knows that bears are the world's greatest hibernators, right? Wrong (like so many things everybody knows). Technically, bears don't hibernate. They sleep a lot in winter, but their body temperature doesn't drop much. Also, they wake up on most days to putter about the cave. What bears do is called "daily torpor."

Daily torpor is as mystifying as hibernation. During torpor, bears don't eat or drink for months, and they sleep nearly nonstop. If people did this, they would starve or die of dehydration, and if they did survive, their muscles would be so shrunken they'd have a hard time standing up. But none of this happens to other animals. Why?

Here's the key. Normally, bears and groundhogs burn carbohydrates for energy, just like us. When the carbs run out, they burn protein, just like us. Converting protein to energy produces a waste called urea, which is poisonous, so we get rid of it. That's what urination is about. If you can't evacuate the urea in your system you can die of ureic acid poisoning.

When bears are in torpor, however, they burn fat. So do groundhogs and their cousins in hibernation. This is why these beasts all gorge before going under. Groundhogs eat a pound a day and double their weight. Bears consume 20,000 calories a day, about five times their normal intake, and put on a layer of fat five inches thick. Burning fat produces no urea and releases water. So hibernating creatures don't need to drink or urinate. And since they don't burn protein (a building block of muscle), their muscles stay relatively firm. On top of which, they're nearly dead anyway, so they don't need much energy.

Hibernating humans?
Wouldn't it be great if humans could hibernate? They might ... someday.

In fact, NASA is looking into it. Hibernation might be a way to send a crew of astronauts to another solar system--a journey that could take centuries.

Doctors are also interested. They'd like to be able to hibernate a single organ. It would be a way to preserve a heart or a kidney for transplantation.

The United States Army is the most interested of all. No, they're not looking for a weapon that could put the enemy out for the winter. Rather, they think hibernation might be useful for transporting wounded soldiers from battlefields to hospitals.

And that day might be close. Thanks to army-funded research, scientists at the University of Minnesota have identified the hibernation gene. What this gene does is produce an enzyme, and what this enzyme does is switch the body over from burning carbohydrates to burning fat. Long-term human hibernation, the kind we'd need for space travel, is still a long way off, according to Dr. Matthew Andrews, a leader in hibernation research. But the technology for short-term human hibernation? Coming soon.

It's true about the groundhog
Groundhogs rarely come out of hibernation on February 2. If it's cold, they might not come out until March. I know, I know. We've seen them popping out of the ground on TV, but appearances can be deceiving. News crews (shockingly!) have been known to wake up a groundhog and drag it out for its photo opportunity.

But a close look at hibernation suggests that there might be more to the groundhog story than I've let on. Hibernation is not a constant state but a cycle. The creature goes into hibernation, comes out, and goes back in again. At the top of its cycle, it may even awake for a few minutes. One reason for this waking is to check the temperature, which is a groundhog's main cue for when to start or stop hibernating.

But way down in a groundhog's burrow, the temperature doesn't change with the weather. A groundhog has to come outside to see if it's spring yet. If it isn't, it goes down for another cycle. The cycle, however, does not run six weeks, as in the legend. Groundhogs rouse themselves from hibernation about every two weeks.

Another interesting fact: According to meteorologists, on a given day the temperature tends to be colder if it's sunny and warmer if it's cloudy.

Put all these facts together and what have you got? Punxsutawney Phil. On a tighter schedule.

Oh, except for one thing. A warm day in early February has nothing to do with whether winter is over. A Canadian researcher did a careful study and found that the groundhog gets it right about 37 percent of the time.

If my whole reputation depended on predicting spring and I got it wrong 63 percent of the time, I'd rather be hibernating, too.