Marmota monax (Linnaeus, 1758)

Common Name and Relative Size

Marmota monax, commonly called the groundhog or woodchuck, is the largest sciurid in most of its geographical range. The only exception is in British Columbia, where its size is comparable to its somewhat larger close relative, the hoary marmot.

Body Length Measurements

Adult groundhogs have a total length ranging from 41.8 to 68.5 cm (16+7⁄16 to 26+15⁄16 inches), which includes a tail that measures between 9.5 and 18.7 cm (3+3⁄4 to 7+3⁄8 inches).

Adult Weight Range

Adult weights typically fall between 2 and 6.3 kg (4 lb 7 oz to 13 lb 14 oz). On average, males are slightly larger than females.

Seasonal Weight Variation

Like all marmots, they are much heavier in autumn, during their seasonal period of autumn hyperphagia, than they are when they emerge from hibernation in spring.

Male Average Weights

Year-round, adult males have an average weight of 3.83 kg (8 lb 7 oz), with an average weight range of 3.1 to 5.07 kg (6 lb 13 oz to 11 lb 3 oz) from spring to fall.

Female Average Weights

Adult females have a year-round average weight of 3.53 kg (7 lb 13 oz), with a spring to fall average weight range of 3.08 to 4.8 kg (6 lb 13 oz to 10 lb 9 oz).

Weight Cycle Patterns

Seasonal weight changes correspond to the yearly cycle of depositing and using body fat. Groundhogs gain increasingly more weight each year for their first two to three years of life, after which their weight stops increasing and plateaus.

Incisor Growth and Wear

Groundhogs have four incisors that grow 1.5 millimetres (1⁄16 inch) per week, and constant use of these teeth wears them down by about this same amount each week.

Incisor Coloration

Unlike the incisors of many other rodents, groundhog incisors are white to ivory-white.

Digging Adaptations

Groundhogs are well adapted for digging, with powerful short legs and broad long claws.

Tail Characteristics

Their tail is shorter than the tails of other members of the Sciuridae family, making up only about one-quarter of their total body length.

Habitat Type

Unlike other marmot species that occupy rocky, mountainous areas, the groundhog lives in lowland habitats.

Geographic Range and Habitat Preferences

It has a wide geographic range, and prefers open country and woodland edges. It is rarely found far from the entrance of one of its burrows.

Common Habitats

Common habitats for groundhogs include small woodlots, low-elevation forests, fields, pastures, and hedgerows.

Burrow Characteristics

They build their dens in well-drained soil, and most individuals maintain separate summer and winter dens.

Population Trends

Increased food access and abundance from human activity has allowed Marmota monax populations to thrive.

Social Organization

Among all marmot species, groundhogs are the most solitary. They do live in aggregations, and their social organization varies between different populations.

Mating Interactions

Groundhogs do not form stable, long-term pair bonds, and interactions between males and females during mating season are normally limited only to copulation.

Regional Social Variation

However, groundhogs living in Ohio have been observed to have a different social organization than populations elsewhere; in Ohio, adult males and females associate with one another throughout the year, and often across multiple years.

Breeding Age

Most groundhogs first breed during their second year of life, though a small portion may breed in their first year.

Breeding Season Timing

Their breeding season runs from early March to mid- or late April, immediately after hibernation ends.

Mating System

Woodchucks are generally described as polygynous, but only female alpine marmots and female woodchucks have been documented mating with multiple males.

Gestation Period Den Behavior

During the 31- to 32-day gestation period, a mated pair shares the same den. As the April or May birth of the litter approaches, the male leaves the den.

Litter Frequency and Size

Females produce one litter each year. Litters contain between one and nine offspring, and most litters have 3 to 5 pups.

Juvenile Emergence

Once the pups have grown a full coat of fur and gained the ability to see, the mother introduces them to the outside wild. At this point, if the father returns to the family group at all, he will do so now.

Juvenile Dispersal

By the end of August, the family group breaks up, and most young groundhogs scatter to dig their own independent burrows.