10 facts you didn’t know about groundhogs

There's more to the furry mammals than Groundhog Day.

Each year groundhogs enjoy 15 minutes of fame—and then most people proceed to forget about them completely. Held every year on February 2, Groundhog Day is a unique U.S. celebration in which people turn to these mammals to predict the weather: If the groundhog sees its shadow on that day, lore has it there will be six more weeks of winter. But what else is there to know about these annual celebrities? Here are some little-known facts.

They're related to squirrels.

Groundhogs (Marmota monax) are a type of rodent known as a marmot, and marmots are closely related to squirrels. "They are giant ground squirrels is what they are," says Richard Thorington, curator of mammals at the Smithsonian National Museum of Natural History in Washington, D.C.

What's more, groundhogs have an extensive range and can be found all over North America.

"[Groundhogs are] the most widely distributed marmot of all of them, [with a range stretching] as far south as northern Alabama to northern Canada—and some are even found in Alaska," says Stam Zervanos, retired professor of biology at Pennsylvania State University in Reading, who's conducted extensive research on groundhogs.

They’re filling in for hedgehogs.

While the reported origins of Groundhog Day are many, the concept is thought to be linked to the Germanic tradition of Candlemas Day, a Christian feast day. According to the folklore, a sunny Candlemas Day means a longer winter. In Europe, however, the animal used was generally a hedgehog or a badger. How it wound up being the groundhog’s responsibility in the U.S. may have been a bit of a fluke.

"When the Europeans came over here, they didn't have any hedgehogs or badgers to lay the blame on, so I think the groundhog got it by being here and being a good size," speculates Thorington. "He became the one to prophesize whether winter would come or not."

There's a movement to replace them with robots.

Some animal rights groups have long taken issue with Groundhog Day, arguing that these shy animals should not be put on display or interrupted from their natural hibernation cycle. Now, PETA is arguing to replace groundhogs with robot groundhogs equipped with artificial intelligence that detects shadows.

'Woodchuck' has nothing to do with wood.

Groundhogs have many colorful names, including "whistle-pig" for their tendency to emit short, high-pitched whistles. They're also known as land beavers, but their most famous nickname is woodchuck.

Surprisingly, the name woodchuck doesn't have anything to do with wood. It's thought to be a corruption of the Native American words wejack, woodshaw, or woodchoock. It may have its roots in the Algonquian (or perhaps Narragansett) name for the animal: wuchak.

Other sources claim it's a bastardization of the Cree word otchek for "fisher" or the Ojibwe ojiig, also for "fisher" or "marten," which Europeans appropriated and misapplied to the groundhog.

So how much wood could a woodchuck chuck? None, apparently.

They build impressive homes.

A groundhog's burrow can be anywhere from eight to 66 feet long, with multiple exits and a number of chambers.

There can be several levels to their burrows, says Zervanos. "They have a burrow for hibernating, and then they have another section of the burrow that's more like their summer home where they can come out more easily."

Their burrows even have separate rooms for defecation—otherwise known as bathrooms.

In some cases, groundhogs have more than one residence and move from one burrow to another.

Farmers consider them pests.

Those impressive tunneling skills make for great burrows, but they can also mean big headaches for those who work in agriculture.

"They dig fairly extensive burrows, and tractors can break an axle [driving over them]," says Zervanos.

And since the animals are herbivores—and prefer tender, young greens—they can make nuisances of themselves by raiding crops.

Soybeans, corn, family gardens—it’s all a banquet in the eyes of a groundhog. But some can be more discerning.

"They’re selective," says the Smithsonian's Thorington. "They’ll go for your best cabbages and best foods that you have out there."

They're loners.

Unlike some of their cousins, such as prairie dogs, groundhogs are basically loners, seeking out their own kind only to mate. (See "Video: Why do prairie dogs do ‘the wave?")

"They’re pretty solitary for most of the year, so the male has no clue where the female is most of the year except when they’re ready to mate," says Penn State’s Zervanos.

Even their maternal duty to their young is short and sweet.

"The mother nurses the young, and then shortly after they’re weaned, they tend to go off on their own. [They're] about as asocial as you can get," says Thorington.

When they sleep, they really sleep.

Groundhogs are known as "true hibernators," going into a dormant state—in which their body temperature and heart rate fall dramatically—from late fall until late winter or early spring.

"True hibernators are the ones that can reduce their body temp below 20 degrees Celsius [68 degrees Fahrenheit]," says Zervanos. "Bears, for example, only drop their body temp to 30 degrees from 37 degrees Celsius [86 from 98.7 degrees Fahrenheit].

"Any of the true hibernators can [also] reduce their heart rate down to about five beats a minute, and their body temperature can go as low as [41 degrees Fahrenheit]," he adds.

But Zervanos, who’s studied groundhog hibernation extensively, points out that hibernation isn’t as cut and dried a process as people think.

"Hibernation is not a deep sleep that continues for the entire winter," explains Zervanos. Instead, groundhogs go through bouts of "torpor," when their body temperature drops to about five degrees Celsius, he says. They’ll do this for about a week, then wake up for three or four days, then go back into torpor.

"They do this about 12 to 20 times in the hibernation season," says Zervanos.

But they wake up early for love.

Groundhogs hibernate from late fall for roughly three months, then wake up when it's still quite cold.

But it turns out they have a very good reason to drag themselves out of bed. There's evidence that male groundhogs wake up early to get a head start on reproduction.

"The males come out and start to prepare for the mating season," says Zervanos, which involves surveying their turf and making house-calls to female burrows as early as February.

"Typically, there’s a male that has a territory that includes several female burrows. And there’s some competition for that territory," he explains. "They try to defend that territory, and they go from burrow to burrow to find out if that female is still there."

Having determined where his potential mates are, the male then returns to his burrow to sleep for another month or so until early March when it’s time to mate.

They have great timing.

Groundhogs display an uncanny knack for good timing.

Groundhogs have to know just when to emerge from hibernation to mate so that their offspring will have the best chance of survival.

"Most matings happen in a ten-day period in early March," says Zervanos. "If [the offspring] are born too late, they can't get enough weight for winter, and if they're born too early, the female doesn't have enough food to feed them."

In other words, the window of opportunity is very small and the wily woodchuck has to get it just right. With those instincts, perhaps it’s appropriate to entrust predictions for the duration of winter to the humble groundhogs.

Follow Stefan Sirucek on Twitter.

This story has been updated. It was originally published on January 31, 2014.

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