In North Dakota muskrats usually have two litters and occasionally three. The gestation period of muskrats is 29 to 30 days. The average litter contains five or six young with litter sizes ranging from one to eleven. The young muskrats, blind and naked at birth, are raised either in a nest chamber within the muskrat house or in a den in the bank. They remain in the nest for three or four weeks when they move out to fend for themselves.
Muskrats weigh less than an ounce at birth and grow rapidly, reaching adulthood in less than a year.
Average adult muskrats weigh from two to two and a half pounds. Muskrats are somewhat active during the day but most of their activity takes place at night. They do not hibernate during the winter but live in relative comfort in their well constructed houses or in bank dens. Both their houses and dens have entrances under the water so even when the area is frozen over, they can swim about and gather roots and stalks of aquatic plants for food. Foliage, roots, and bulbs of aquatic plants such as cattail, bulrush, pondweeds, and sedges.