Scientific name: Marmota monax
Common name: Woodchuck
(Information for this species page was compiled in part by Ben Dickun for Biology
220 at Penn State New Kensington in Spring 2002)
The woodchuck is the third largest North American rodent. It has a great variety of other names including groundhog, whistle pig, marmot, grass rat and earth pig. The species name "monax" is said to be derived from a Native American name for the animal which roughly translates into "the digger." All of these names reflect different aspects of this very abundant and widely distributed animal's behaviors, feeding activities, and habitat preferences.
An adult woodchuck is twenty-six inches long and weighs between five and fifteen pounds. They are, logically, the heaviest at the end of the summer season. Their fur ranges in color from yellowish-brown to reddish-brown to nearly black. Their coats have two types of hairs: an under-fur that is short and wooly and guard hairs that protrude up through the under-fur. Their belly hair is sparse and lighter in color than the rest of their coat.
The woodchuck's ears, eyes, and nose are close to the top of its head. This anatomy enables the animal to utilize all of its very acutely developed faculties of hearing, vision, and olfaction to examine its surroundings with only minimal exposure from its burrow opening. The woodchuck's feet are dark in color (black to dark brown) and equipped with sturdy claws for digging burrows. The feet are flat ("plantigrade") like those of a bear or raccoon. The forefeet have four toes and the hindfeet have five. The woodchuck also has a short, black, bushy tail.
Habitat and Burrow
Woodchucks are found in western and eastern portions of North America. In the east, they range from southern Canada and New England south to Virginia and northern Alabama. In the west they are found from central Alaska through southern Canada, south through northern Idaho and eastern Kansas, and east to north-eastern North Dakota. They live in a great variety of specific habitats from open pastures, fields, meadows and fence rows to forest edges and even deep into the woods. On our Nature Trail there is a large woodchuck burrow right at the top of the ravine trail. There are also several burrows out in the surrounding grass field ecosystems.
Individuals rarely move more than a half mile from their burrows or home ranges.
The woodchuck's burrow, then, is the center of its home range and the focus of much of its efforts and work. Burrows are usually found in sloped, well drained sites. They can be up to five feet deep and over thirty feet long. Typically, the burrow's entrance leads into a steeply angled passage which quickly levels off into a longer, narrower tunnel. The den is found off of this central tunnel and contains both a nest and an excrement chamber. The nest functions as a brood chamber, sleeping chamber, and as a hibernaculum. It is lined with soft grasses for both warmth and comfort.
The burrow will have a main entrance around which the tunneled dirt is piled. It will also have "spy holes", or smaller, more concealed entrances out of which the woodchuck can look across its home range or in an emergency rapidly exit or enter the burrow. The soil from the digging of these spy holes is carried to the dirt midden of
the main entrance to minimize the visibility of these less "public" holes.
The burrows are extremely beneficial to the soil ecosystem. They generate gravitational water channels and extensive aeration passages through the soil profile. They also provide widely utilized habitats for other animals in these ecosystems. Rabbits, opossums, raccoons, skunks and foxes all use abandoned woodchuck burrows for dens and refuges. These burrows, though, can also be a serious problem for larger, grazing animals. The larger entrances, the hidden burrow openings, and the weakend soil structure over the tunnel systems can be serious hazards for larger animals especially when they are running across the surface of the soil.
Woodchucks eat a great variety of foods including clover and alfalfa (probably their two favorites!), sheep sorrel, timothy, buttercup, tear thumb, dandelion, agrimany, red and black raspberries, buckwheat, plantain, wild lettuce, hawk weed, Indian paintbrush, daisies, green grasses, corn in the milk stage, garden vegetables (another GREAT favorite!), any number of both wild and cultivated fruits, and the leaves, bark, and fruits of the wild cherry. Woodchucks forage and eat at almost any time of the day. In the summer they often fall into a pattern of early morning and late evening activity in order to avoid the heat of the day. They can eat up to one third of their body weight a day! Woodchucks are not known to drink water but instead are thought to obtain moisture from rain and dew covered vegetation and moist grasses. While eating they raise their heads every ten seconds or so to check the area for predators or danger. They are organisms of patterns and habits that wear down four to six inch wide, very prominent trails between their burrows and their favorite feeding areas.
Woodchucks can live up to ten years though very few reach advanced ages like this in the wild. Although they are good runners and are capable of climbing trees and even swimming to avoid dangers, their many predators (especially foxes, coyotes, owls, hawks, domesticated dogs, and humans) take their toll on the woodchuck population especially on the very young cohorts or the older, or less fit individuals.
Woodchucks are true hibernators and spend nearly half of the days of a year in a hibernative state. During hibernation a woodchuck will breathe about once every six minutes and maintain a body temperature of about 38 degrees F (normal temperature is 96.8 degrees F). During hibernation males will lose about 47% of their body weight and females about 37% of their body weight. The higher loss rate in males is thought to be due to energy consumed by spermatogenesis during hibernation. Woodchucks enter hibernation usually by November and will not emerge until March or early April (in spite of the February timing of "Ground Hog Day!").
Mating and Reproduction
Males are the first to emerge from their dens in the spring. They spend their first few weeks out searching outside of their ranges for receptive females. They enter the females' dens and attempt to mate. The females may accept or reject their advances. Competing males may also fight at the dens of particular females. Males usually live in the mated females' dens throughout the mating season although some older males have been known to just visit the dens a few times a day while maintaining their own home range den. After the mating season ends, all of the males return to their home dens and take no part in the rearing of the young.
Gestation lasts 28 days and the young are born in late April or early May. A typical litter size is four or five pups. The pups emerge from the den after about six weeks. At this time they are weaned and able to eat solid food. In early summer the young move away from the mother into their own burrows that are still located within the mother's home range. By midsummer, though, the young woodchucks move out of this range to look for new territories. This is a period of intense mortality for these inexperienced, vulnerable individuals. Those that survive spend the rest of the summer eating in order to build up the fat reserves needed for the long winter hibernation.