VERTEBRATE PESTS: Have A Happy Groundhog Day

About the time you are reading this, Punxsutawney Phil, the famous groundhog, has either emerged from his burrow in Pennsylvania, indicating an early spring or, he slept in, indicating six more weeks of winter. Cute. But I wouldn’t plan your spring termite work schedule around Phil’s sleeping habits.
But because woodchucks have become common pests in urban areas, pest professionals should be aware of this large squirrel and effective management strategies for it. This month, we’ll review the biology and behavior of woodchucks in urban areas. In part II, next month, we’ll address woodchuck management.

BACKGROUND. The names groundhog, woodchuck and whistlepig all refer to the same mammal. Woodchucks belong to the marmot family. The most prevalent marmot species in the United States is the common woodchuck, Marmota monax. This Latin name is believed to be descriptive of Native American terms referring to the “mouse of the mountain that digs.” The term “woodchuck” is associated with the sound “tchuk, tchuk,” this mammal makes when excited or threatened by a predator and thus was described by native Americans and frontiersman according to the sound it makes.

Woodchucks and other marmots are rodents, belonging to the squirrel family Sciuridae. This mammal family includes tree squirrels and ground squirrels. Marmots are closely related to other ground squirrels such as the chipmunk, the thirteen lined ground squirrel, the California ground squirrel and others.

The woodchuck occurs roughly in the eastern half of the United States, although it is absent in most areas of the Southeast st ates. In the Western U.S., the yellow-bellied marmot, Marmota flaviventris, and several other species occur, but are not as significant as pests as the woodchuck.

The natural habitat of woodchucks includes fields and wooded areas. As humans continue to move into and take over these areas, woodchucks establish their burrows along railroad embankments, ditch banks, roadsides, fencerows, levees and increasingly around and beneath many types of buildings.

Calls to pest professionals (including wildlife damage professionals) regarding nuisance woodchucks can occur from March though August, when homeown-ers may discover a frighteningly large burrow beneath the slab of a foundation or they find their vegetable garden has been consumed during the week.

BIOLOGY AND BEHAVIOR. The woodchuck is a medium-sized mammal weighing between 4 and 14 pounds. They are lightest after emerging from hibernation in the spring and heaviest after stocking up body fat just prior to entering hibernation in the autumn. The body fur is long, coarse and grizzled grayish-brown in color. White woodchucks, or woodchucks with large patches of white, are occasionally seen, misleading farmers, homeowners and even wildlife damage professionals that perhaps a badger (another animal that “hogs the ground”) is active in the area. Sometimes, woodchucks active along creeks and streams are mistaken for beavers.

Woodchucks have short, powerful legs, small ears and a short, bushy tail. Four sharp-clawed toes are present on each front foot with five toes on the hind feet. Its short, stocky appearance gives the impression that the woodchuck crouches close to the ground as it moves about (i.e., “ground”hogs). Like most other rodents, the woodchuck’s skull is characterized by a prominent pair of incisors used for cutting and clipping through roots, stems and vegetation, as well as for defense.

For the most part, woodchucks are vegetarians, consuming various types of green, leafy vegetation, pasture, forage and vegetables. Clover, dandelions and plantain are among the common foods in fields. Healthy adults can consume between 1 and 1½ pounds of vegetation daily. Thus, suburban woodchuck populations can cause severe and wide-scale damage to vegetable and flower gardens quickly.

The greater part of a woodchuck’s day and night is spent in the burrow — presumably sleeping. Feeding periods vary according to weather conditions and the season. During the cool days of early spring, the woodchuck is most active during the warmer parts of the morning and afternoon. If the day is unseasonably cold or wet, the woodchuck may not emerge at all. During the summer, the animal avoids the heat by remaining in the cool burrow during the day and feeding during early morning and again at dusk.

Woodchucks enter hibernation beginning mid-October and emerge during February. Woodchucks kept in captivity, even in outdoor pens, may never hibernate at all and remain sporadically active throughout the winter. After emerging from their winter den, woodchucks mate and the female produces a single litter of four to six young born a month later (March to April). The young leave the nest in early July to establish their own burrows and territories.
Woodchucks are also known as whistlepigs because of their ability to whistle. Whistling is a common vocalization among other ground squirrels and prairie dogs. Adult female woodchucks have been observed by researchers to warn their litters by whistling when they detect the presence of large predators or hear the barking of dogs. This whistling alerts the pups to scurry back to the den for safety.

In suburban areas where food and good den locations exist, a healthy woodchuck can live for up to six years and even longer. However, most die sooner from cars, large dogs, natural predators, flooding of their burrows from rains and the control efforts of homeowners and pest professionals.

BURROWS. When woodchucks establish themselves around residential and business developments, there is plenty of reason for concern. Burrows established beneath building foundations, patios, walkways, streets, decks, garages, carports and other structures can cause significant undermining of a structure. The burrows and tunnels of woodchucks can be large and extensive and the amount of soil excavated from around a foundation can be serious. Even when woodchucks are captured or killed, replacing the hundreds and even thousands of pounds of soil beneath a foundation is not possible.

The main tunnel opening is about 12 inches in diameter, but narrows to about 6 inches further into the system. Most tunnels are constructed within 2 to 4 feet of the surface, but occasionally drop down as deep as 6 feet. A burrow system can be from 10 to 45 feet in length depending on the age of the woodchuck and how often the system has been re-used over the years. The nest is often located deep into the burrow system.

The main entrance to the burrow is characterized by a large mound of soil sometimes as large as 4½ feet in diameter. The woodchuck uses this mound area for sunning, resting, surveying his surroundings and as a latrine. When the burrow is active, often the dirt around the opening will be fresh and dark in appearance. Often, feces are present or the soil will have a characteristic musky urine smell.

TERRITORIES. Typically, one or two adult woodchucks occupy an area of about one acre, although several woodchucks can exist in a new suburban development in a crop field or some other large field. Their daily foraging patterns will take them 20 to 30 yards from their dens, but if resources become scarce or spread out and predators are not about, they can be seen foraging several hundred yards away from the main den. In some cases, the woodchuck will establish auxiliary dens away from the main den and use these sporadically. As we will see next month, this behavior is important relative to control efforts. Woodchucks defend their dens against other woodchucks except during times of breeding and family rearing (March to July) when the adult males, females and young occupy the same den.

Next month, we will examine management strategies for the woodchuck in urban areas. In the meantime, I hope you had a wonderful Groundhog Day!

Editor’s note: Part 2 of this column will appear in next month’s issue of PCT.

The author is president of RMC Pest Management Consulting. He can be reached at rcorrigan@pctonline.com.