Groundhog (Marmota monax): Woodchuck Facts and Habitat

What kind of animal is a groundhog?

The groundhog is a rodent in the squirrel family, Sciuridae, which also includes tree squirrels, chipmunks and prairie dogs. Within this family it belongs to the marmots, the biggest ground squirrels of all. Most marmots, such as the hoary marmot and the Alpine marmot of Europe, live high in the mountains. The groundhog is the exception: it is a lowland marmot of farmland, meadows and woodland edges.

The animal goes by many names, including woodchuck, whistle-pig and land beaver. The word “woodchuck” has nothing to do with wood. It comes from an Algonquian name for the animal. The story of these names is told in Is a groundhog the same as a woodchuck?.

Appearance

A groundhog has a stocky, rounded body, short powerful legs and a short, bushy tail about a quarter of its body length. Its fur is grizzled grayish-brown to cinnamon or dark brown, with pale-tipped guard hairs that give it a frosted look. The feet are dark brown to black, and the front feet carry long, strong claws for digging.

The head is broad with small, rounded ears that can close over the ear opening to keep out soil. Like all rodents, the groundhog has four large incisors that grow continuously, about 1.5 mm (1/16 in) a week, and are worn down by gnawing. Unusually for a rodent, its incisors are white to ivory rather than orange-yellow. All-black and all-white groundhogs occur occasionally.

How big is a groundhog?

The groundhog is the largest member of the squirrel family across most of its range. Adults measure about 42–68 cm (16.5–27 in) from nose to tail tip, including a tail of about 10–19 cm (4–7.5 in). They usually weigh 2–6.3 kg (4.4–14 lb).

Weight changes greatly with the seasons. A groundhog is lightest when it comes out of hibernation in late winter and heaviest in early autumn, after months of feeding to build up fat. Males are slightly larger than females on average.

Habitat and range

Groundhogs live across much of the eastern and central United States, south to Georgia, Alabama, northern Louisiana and eastern Oklahoma, and north across southern and central Canada to Yukon and central Alaska. They do not live in the western United States, where other marmots take their place in the mountains.

Their favorite habitat is open country next to cover: woodland edges, hedgerows, fields, pastures, meadows, stream banks and roadsides. Clearing forests for farms and roads has created lots of this edge habitat, so groundhogs are probably more common today than before European settlement. They live comfortably in suburbs, parks, cemeteries and golf courses.

Diet

Groundhogs are herbivores that feed mainly on green plants. Favorite foods include clover, alfalfa, grasses, dandelion, plantain and coltsfoot, as well as berries, fruit, vegetables, leaves and bark. They occasionally eat insects, snails and even bird eggs, but much less often than most squirrels.

An adult can eat more than 0.45 kg (1 lb) of plants a day. In summer, groundhogs eat heavily to put on fat for winter, sometimes increasing their body weight by around half or more. They do not store food in their burrows. Groundhogs get much of their water from juicy plants and dew.

Burrows

Groundhogs are expert diggers. A typical burrow has two to five entrances, including a main entrance marked by a mound of soil and a hidden escape or “spy” hole. Tunnels can extend more than 14 m (46 ft) when side galleries are included, and the deepest parts can lie about 1.2 m (4 ft) below ground. Inside are a nest chamber lined with dry grass and leaves and a separate toilet chamber.

Many groundhogs keep a summer burrow in an open field near food and a winter burrow in woods or brush, where they hibernate below the frost line. Abandoned groundhog burrows become homes for many other animals, including red foxes, skunks, raccoons, cottontail rabbits, chipmunks, snakes and even river otters. By moving large amounts of soil, groundhogs also help mix and aerate it.

Behavior and hibernation

Groundhogs are active by day and feed mainly in the morning and late afternoon. They spend much of their time near a burrow entrance, often sitting bolt upright on their hind legs to watch for danger. When alarmed, they give a loud, high-pitched whistle, which is the origin of the name “whistle-pig”. They also chatter their teeth, bark, squeal and hiss.

Despite their bulky build, groundhogs can climb trees to escape predators or look around, and they swim well. They are the most solitary of the marmots. Adults defend their own space, and dominant males hold home ranges that overlap those of several females. When two groundhogs meet, they may touch noses in greeting, or one may arch its back, raise its tail and bare its teeth as a threat. Scent from glands on the face and near the tail helps mark territory.

Social life varies from place to place. Most studies describe adult males and females meeting only to mate, but long-term research in Ohio found some males and females associating with each other through the year and even from one year to the next. Young groundhogs that leave their mother often dig several short, unused holes nearby before settling, which can make an area look like a colony.

The groundhog is a true hibernator. From about October or November to February or March, it sleeps in its winter burrow. Its body temperature falls from about 37 °C (99 °F) to just a few degrees above freezing, and its heart slows from around 80 beats a minute to as few as 4–10. Breathing becomes very slow, with long pauses between breaths. From time to time, typically every several days to a couple of weeks, the animal briefly rewarms to a normal temperature before sinking back into deep torpor. It may lose a third to a half of its body weight by spring, and it emerges with a little fat left to tide it over until fresh plants grow.

Hibernation lasts longer in the north than in the south. In Canada a groundhog may stay underground for five months or more, while in the southern part of the range some animals hibernate only briefly or stay active in mild spells. Find out how this works in Do groundhogs hibernate?.

Reproduction and life cycle

Males come out of hibernation first, in late winter, and visit the burrows of nearby females. Mating takes place in early spring, from about March to April depending on latitude. Pregnancy is short, lasting only about 31–32 days.

Females produce one litter a year, usually of 2–6 pups, with 3–5 most common and up to 9 recorded. Pups are born blind and hairless in April or May and weigh about 26–27 g (about 1 oz). They open their eyes at around four weeks, start coming out of the burrow at about five to six weeks and are weaned at about 44 days. By late summer the young leave to dig burrows of their own. Most groundhogs first breed at two years old.

How long do groundhogs live?

In the wild, most groundhogs live only two or three years, and few pass six. Predators, traffic and disease take a heavy toll, especially on young animals in their first year. In captivity, groundhogs can live up to about 14 years.

Predators and threats

Natural predators of adult groundhogs include coyotes, foxes, bobcats, badgers, black bears and large dogs, and in the north, wolves and lynx. Young groundhogs are also taken by hawks, eagles, owls, mink and snakes. The groundhog’s main defenses are its burrows, its whistled warning and, when cornered, its sharp incisors and claws.

The groundhog is listed as Least Concern by the IUCN because it is widespread and common. Its main conflicts with people come from eating garden and farm crops and from burrows that can undermine buildings and damage farm machinery.

Groundhogs and people

Each February 2, crowds gather in Punxsutawney, Pennsylvania, to see whether the groundhog Punxsutawney Phil “sees his shadow” and forecasts six more weeks of winter. The custom comes from German weather lore brought to Pennsylvania in the 1800s. Phil’s actual forecasting record is examined in Is Groundhog Day accurate?.

Several other towns in the United States and Canada keep their own forecasting groundhogs, such as Wiarton Willie in Ontario, Shubenacadie Sam in Nova Scotia and Staten Island Chuck in New York City. The 1993 comedy film Groundhog Day, starring Bill Murray, made the tradition famous around the world.

Groundhogs also matter in medicine. Some carry the woodchuck hepatitis virus, which closely resembles human hepatitis B, so captive-bred woodchucks have been important in research on hepatitis B and liver cancer. Their hibernation is studied for insights into metabolism and obesity.

Myths and facts

Myth: groundhogs predict the weather. Studies comparing Groundhog Day forecasts with real weather find no useful predictive power.

Myth: woodchucks chuck wood. They do not throw or eat wood. The tongue twister is wordplay on a name borrowed from an Algonquian language.

Fact: groundhogs are true hibernators. Unlike bears, which stay relatively warm in winter, groundhogs drop their body temperature close to freezing for months.