Saturday, May 23, 2009

Natural History of Groundhogs

The groundhog or woodchuck (Marmota monax) is a husky, waddling rodent in the squirrel family Sciuridae, order Rodentia. The groundhog is a type of marmot (genus Marmota), and is also closely related to the ground squirrels and gophers. The natural habitat of the groundhog is forest edges and grasslands, ranging from the eastern United States and Canada through much of the Midwest, to parts of the western states and provinces. However, the groundhog is also a familiar species in agricultural landscapes within its range, occurring along roadsides, fence-rows, pastures, the margins of fields, and even in some suburban habitats.

The groundhog is a rather large marmot, typically weighing about 6.6-13.2 lb (3-6 kg). The fur is red or brown, with black or dark brown feet. They have a plump body, a broad head, and small, erect ears. The tail and legs are short, while the fingers and toes have strong claws, useful for digging. When frightened, groundhogs can run as fast as a person, but they are normally slow, waddling animals, tending to stay close to the safety of their burrows. They can climb rather well, and are sometimes seen feeding while perched in the lower parts of trees or shrubs.

Groundhogs are enthusiastic diggers, and they spend much of their time preparing and improving their burrows and dens. Woodchucks dig their burrow complexes in well-drained, sandy-loam soils, generally on the highest ground available. Their sleeping dens are lined with hay-like materials, both for comfort, and to provide insulation during the winter. There are separate chambers for sleeping and defecation.

Groundhogs are social animals, sometimes living in open colonies with as many as tens of animals living in a maze of interconnected burrows. They are are not very vocal , but they will make sharp whistles when a potential predator is noticed. This loud sound is a warning to other animals in the colony.

Groundhogs are herbivorous animals, eating the foliage, stems, roots, and tubers of herbaceous plants, and sometimes the buds, leaves, flowers, and young shoots of woody species. They also store food in their dens, especially for consumption during the winter. Groundhogs are very fat in the autumn, just prior to hibernation. If they are living in a colony, groundhogs snuggle in family groups to conserve heat during the winter. They occasionally waken from their deep sleep to feed. However, groundhogs lose weight progressively during their hibernation, and can weigh one-third to one-half less in the springtime than in the autumn.

Groundhogs have a single mating season each year, usually beginning shortly after they emerge from their dens in the spring. After a gestation period of 30-32 days, the female usually gives birth to four or five young, although the size of the litter may vary from one to nine. Born blind and naked, young groundhogs acquire a downy coat after about two weeks. Soon the mother begins to bring soft plant stems and leaves back to the den for them to eat. Young groundhogs follow their mother out of the burrow after about a month and are weaned about two weeks later.

Groundhogs are sometimes perceived to be pests. They can cause considerable damage by raiding vegetable gardens, and can also consume large quantities of ripe grain and other crops. In addition, the excavations of groundhogs can be hazardous to livestock, who can break a leg if they step unawares into a groundhog hole, or if an underground burrow collapses beneath their weight.For these reasons, groundhogs are sometimes hunted and poisoned. However, groundhogs also provide valuable ecological benefits as prey for a wide range of carnivorous animals, and because these interesting creatures are a pleasing component of the outdoors experience for many people.

for 'groundhogs in the city', see comment.

1 comment:

  1. URBANA, Ill.(January 28, 2009) -

    According to a University of Illinois study, groundhogs, also known as woodchucks, may have a better survival rate in urban settings than in rural areas.

    The study is being conducted in response to a request from the Illinois State Department of Natural Resources for current data on how woodchucks are responding to changing land-use practices.

    Liza Watson, U of I graduate student in wildlife ecology in the College of Agricultural, Consumer and Environmental Sciences, has been tracking both urban and rural woodchucks for nearly two years.

    "I'm looking at how they're adjusting in urban settings by examining their survival rates, movements, and their general vigilance behavior," Watson said. She explained that vigilance behavior is when they are alert and scanning the landscape for predators.

    Woodchucks primarily rely on their sight to spot a predator rather than scent, so if there is any kind of disturbance, they stop what they're doing and look in that direction.

    "If you're standing up on your hind legs all the time looking for predators, you can't be feeding, and in order to survive hibernation, they need to spend as much time as possible feeding during the active season. There's only so much time in a day, so there's a trade-off there. If they're living in an urban setting, they might be less vigilant because they've become habituated to human disturbance and so they can spend more time foraging for food," Watson said.

    Watson trapped 41 adult woodchucks. The animals were anesthetized and surgically implanted with tiny radio transmitters. The implants allowed Watson to follow each animal and to know which of the 41 animals she was observing.

    "In the summer, they tend to be active in the early evenings, so I'd drive around looking for them and I videotaped them from the vehicle, at least 30 meters away. They typically don't respond to cars, so as long as I stayed in the truck, I could observe them without disturbing them," she said.

    The transmitter has a mortality sensor so it beeps slower if the animal hasn't moved in over eight hours. "We can bring them back to the vet school where they conduct a necropsy to determine how they died," Watson said. Currently there are 22 remaining from the original 41 that were tagged.

    "In rural areas, we think most deaths were caused by a predator, such as a coyote, because we'd find just the transmitter and some remains," Watson said. Four of the rural animals also died in hibernation. "This usually means that they didn't have enough fat stores when they entered hibernation. They're herbivores, so even if they did wake up early from hunger and come out, there wouldn't be anything green enough to eat."

    Woodchucks eat grass, clover, dandelion, some garden vegetables and some agricultural crops.
    The question is - does urbanization give the woodchucks a natural buffer zone to protect them from predators?

    Schooley says yes. "We also think that woodchucks may know that urban settings are not as risky an environment. We're trying to see whether they have become habituated to humans. You've seen a tree squirrel that you can get within a foot of before they run. In the same way, if woodchucks become habituated to humans, they'll realize that urban areas are safe and be able to be less vigilant and feed more," Schooley said.

    The study also looked at how far woodchucks travel from their burrow. In the city and residential areas, woodchucks have fewer natural predators and food available from gardens and plantings, but the flip side is that their habitat is fairly fragmented. The study found that urban woodchucks have restricted movements and consequently smaller home ranges than rural woodchucks.

    Funding for the research was provided by the University of Illinois and grants from the American Society of Mammalogists and the American Museum of Natural History.

    So, it looks like the groundhog that just showed up in my backyard is likely to be around for awhile.