Like most of the 14 marmot species (5), the Olympic marmot is a highly social animal (7) (10), living in groups of between 3 and 20 individuals within underground burrow systems (9). A typical Olympic marmot colony is composed of a male, two females and their young (5) (6) (7) (10). The young, known as pups (6), are usually a mixture of ages, and generally consist of a litter of yearlings and a litter of infants (7) (10).
The Olympic marmot is a diurnal species (4), foraging in the morning and afternoon for a variety of vegetation types (7). This species tends to favour fresh plant growth (6) (14), and grasses and forbs appear to be the most important components of its diet (7) (14). Roots, herbs, mosses, flowers and even the occasional insect are also eaten (7). Olympic marmots are capable of doubling their body weight during the summer, and they use up the copious amounts of stored fat during hibernation (6). Dry grasses are sometimes collected by the Olympic marmot and taken into the burrow system to be used as bedding or for food (7).
Before the start of each feeding period, the Olympic marmot visits the other burrows in the colony (7). This species has a series of face-to-face interactions which serve as a regular greeting ritual (10), and family members engage in nose-to-cheek greetings (7) (8), as well as grooming (8).
The Olympic marmot is only active during the months of June, July and August (7), and typically hibernates between September and May (3) (7) (8) (13). It is believed that Olympic marmots undergo two moults per year. The midsummer moult turns the coat almost black, while during hibernation the marmots become pale again, and emerge in the spring with yellow-brown fur (6) (13).
Shortly after emerging from hibernation, the mating season begins (10). Generally, a female Olympic marmot will have one litter every other year (5) (7) (8) (10) (14), but there is evidence that females may sometimes breed in consecutive years (9) (15). Between April and June, following a gestation period of around 30 to 32 days, a litter is born in a grass-lined nest (10). The average litter size of the Olympic marmot is four (7) (10). The young do not emerge from the nest until they are about one month old (10), and they remain with the colony until they are two years of age (5) (7) (8) (10). When they first emerge, the pups initially stay close to their burrows, but gradually stray further afield and become more active later in the summer (6).