Home ranges of the long-tailed marmot average about and contain about three burrow systems (range one to six). In a chamber in one of these burrows the marmots hibernate from about September to April or May, a period during which the ground is covered with snow for much of the time. Different burrows may be used for hibernation in different years. Mating occurs in late April and early May and may take place underground before the marmots emerge from the burrow after the winter. The gestation period is about four and a half weeks and the litter of about four pups emerges from the nest at about six weeks of age. Only about half of the pups survive the summer, some being consumed by predators and others being killed by adult males joining the group. Most adults survive the hibernation period but a rather higher proportion of juveniles die during their first winter. Females do not usually breed as three-year-olds but wait till the following year.