Call it a woodchuck, whistle pig, whistler or groundhog -- this big rodent is really a squirrel. Taxonomists assign the groundhog to the family Sciuridae, which embraces all tree squirrels, ground squirrels, prairie dogs and marmots. The familiar groundhog is one of 14 species of marmots that inhabit grasslands, forests and mountains around the world.
As a habitat generalist, the American woodchuck lives in a wide range of environments from the mid-South to central Alaska. In Pennsylvania it was originally a deep forest dweller, but its ability to adapt to different landscapes enabled the groundhog to thrive in agricultural and even suburban settings. It is common in all the state's 67 counties.
Groundhogs are most active during daylight hours, foraging in warmer months for grasses, flowers and cultivated crops where available. If disturbed, they can stand erect and motionless for several minutes to identify the danger and may emit a shrill whistle when alarmed.
The groundhog is one of the few Pennsylvania mammals that are true winter hibernators. In late autumn, chucks retire to a den lined with leaves and grasses, plug the entrance with earth and enter a deep metabolic sleep. Body temperature falls to a constant 40 degrees, about 57 degrees lower than when the animal is active. Breathing slows and a chuck's heart rate falls to four beats per minute. Perhaps contributing to legend, groundhogs do, however, arouse and venture forth during spells of mild weather.
Females produce one litter per year. Litters of two to nine young are born in April or May, often in a different den from the one used by the mother for hibernation.
Groundhogs can exceed 2 feet in length and weigh nearly 12 pounds. They can infest favorable habitats, especially alfalfa and clover hay fields, at a rate of as many as 10 chucks per acre. In addition to direct damage to crops, woodchucks in farm settings also jeopardize livestock. Cattle and horses are sometimes injured by stepping into holes groundhogs excavate for dens.
In Pennsylvania, groundhogs are considered small game and are a popular quarry for some hunters. Generally, marksmen who prize precision shooting seek the rodents at long range with light-caliber rifles. There is no closed season, except that groundhogs may not be hunted during the regular firearms deer season. Groundhog hunting is most popular in mid-summer when hay fields are newly mowed and visibility improved. Groundhogs may not be hunted on Sunday.