Hibernation: Deeeeeeep sleeeeeeeep

 


1. Chillin' out

2. Cold trance or transplant?

3. Stroke of luck

4. Waking, meeting, sleeping, mating

A lady groundhog stands before her burrow to greet a gentle-hog caller. G'hogs, or woodchucks, temporarily leave hibernation in early spring to play "let's get acquainted." It's a preliminary step toward mating, which usually occurs just after hibernation ends. Photo: Stam. Zervanos, Penn State University

Because groundhogs must reproduce on schedule, males take a break from hibernating to romance the ladies.


He wakes. He courts. This is news?
Tell the truth: Isn't groundhog day the ultimate snooze-news? What could be more boring than Feb. 2, when Phil the groundhog quits hibernating, grabs a quick cuppa joe and staggers out of his hole? If Phil sees his shadow, he slinks back into his pied a tierre, and winter rules for another six weeks.

Otherwise, he ends his long "nap" and gets ready for spring: polishing the car, checking his bet in the NCAA pool, and prowling for female talent.

Sorry. When winter ends, guy groundhogs don't think about shadows, cars, or even college ball. But they do think about spreading their genes.

2 big, round, bush tailed brown furry groundhogs stand nose-to-nose

At least, that was the result of a study by Penn State biologist Stam Zervanos, who tracked 32 groundhogs for four years on an experimental farm in Pennsylvania. Using radio collars, remote readings of body temperature and groundhog-sensing cameras, he noticed that, toward the end of winter, male groundhogs -- AKA woodchucks -- devoted one of their regular periods of arousal to defending territory and meeting groundhogs of the female persuasion.

Furiously flirting
Arousal is a strange term for a strange interlude in hibernation, when body temperature returns to normal and the animals "wake up" for a while. The explanations for arousal may include:

Dumping body waste, which can accumulate even at extremely low metabolic rates.

Restoring the biochemistry of cell membranes, which control what enters and leaves cells.

Stimulating the immune systems to attack pathogens.

Catching up on sleep. Honest! Since brains are largely idle during hibernation, the animal may have to "wake up" to so sleep can rejuvenate the brain. This poetic suggestion dates to the 1960s, but it's gotten some recent support, Zervanos says.

In all, the basis for arousal, like the physiological basis for hibernation itself, remains unclear. "Maybe there is not one single reason," says Zervanos.

Rouse 'n romance
Certainly, groundhogs have an important reason for arousal: mating (that sounds logical to us, but Zervanos says he's the first to recognize such behavior during hibernation).

Here's the reason: Groundhogs must precisely schedule their reproduction. If they mate too early in the spring, their young won't be able to find food once they are weaned (after all, they don't shop Safeway). But if the 'hogs wait too late to mate, their young 'uns won't have time to store fat before they stumble into a hole for that long winter "snooze."

To get the timing right, groundhogs must mate immediately after hibernation ends. But females are radically uninterested in the fellas, Zervanos says, and "a period of courtship may be needed for females to select and accept the males, sort of a 'kiss and make up' period."

When the guys arouse themselves and come a-courtin', females emerge from hibernation and they spend some quality time getting acquainted, then they return to separate burrows for more deep snoozing. Finally, after hibernation, "the male ... spends a few days with her, mates, and goes and mates with the next one," Zervanos says. Males and females essentially ignore each other until the following spring.

light-brown thick-bodied groundhog stands before burrow
A female groundhog (woodchuck), emerges from her burrow at a Penn State experimental farm. The raised tail and stand-up hairdo on the back both signal alarm. Photo: June Brown, Penn State University

In terms of energy, this behavior makes sense, says Zervanos. "Energy is one of the key adaptations of an animal to its environment. If an animal can't get enough energy to survive, mate, and reproduce, it's not adapted."

But males and females use their energy differently at this crucial time in early spring. The male "spends long periods totally aroused, spends most of the energy he has saved to visit females and defend his territory," Zervanos says. The female, in contrast, "saves as much energy as possible, because she has to bear the young and feed them."

Translated: She goes downstairs for some serious torpor while the swain patrols his territory, drumming up interest among other ladies and keeping the fellas at bay.

Once males have courted and mated, their reproductive work is done for the year. They can devote their days to betting on the World Series and getting blubbery for the next hibernation. Overall, males hibernate a week or two less than females.

Rhythm method
Zervanos says his study of groundhogs produced clues about the triggers to hibernation. Although the woodchucks may appear half-dead, "They seem to maintain a biological rhythm even during hibernation," he says. The sketchy data "basically show that ... both arousal and the return to torpor seem to occur in the early morning, while the period of hibernation, the number of hours they are in hibernation, appears to be on a 24-hour cycle."

That means some sort of timing mechanism is functioning in the stone-cold, hibernating groundhog. And that, Zervanos says, returns the story to the energy budget. Because groundhogs must mate early in the year, immediately after hibernation, they need to end hibernation in unison, so "Their biological clock still connects, it's still working during hibernation."

Still snoozin'? Then rouse yourself for the hibernation bibliography!

 

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