Types of Beavers in North Dakota

The American Beaver is a large, stocky rodent with a distinctive appearance. Adults typically weigh 40 to 60 pounds, though some individuals exceed 70 pounds in favorable habitats. Their body is covered in dense, waterproof fur that ranges from dark brown to reddish-brown. The most recognizable feature is their flat, paddle-shaped tail, which is hairless and dark gray. Their front teeth are large and orange-colored, visible when they are chewing. Their hind feet are webbed and powerful, adapted for swimming, while their front feet are smaller with strong claws for digging and felling trees.

When swimming, a beaver creates a distinctive V-shaped wake as it moves across the water. You may see only the head breaking the surface, with the nose and eyes visible. The tail sometimes slaps the water as a warning signal before the animal dives. Beavers leave no ripples of movement across their body like a muskrat does; instead, their whole head appears blocky and relatively stationary when observing. Watch for their silhouette near dam or lodge structures, especially near dusk and dawn when they are most active. Fresh wood chips and gnaw marks on trees along the shore are also reliable signs of beaver presence.

American Beavers in North Dakota are among the largest rodents on the continent. Most adults measure 3 to 4 feet in length from nose to tail, with tails adding 12 to 16 inches of that length. Weight varies by habitat quality and age, but 40 to 60 pounds is typical for healthy adults. The largest beavers on record have weighed over 100 pounds, though these are exceptional. Sexual dimorphism is minimal, so males and females are similar in size. Juveniles born in spring reach half-adult size by autumn and approach full size by age three.

American Beavers display a range of fur colors from very dark brown to lighter reddish-brown, with some individuals appearing almost black while others are closer to auburn. Fur color is primarily determined by genetics and diet, with no distinct subspecies or named color morphs. Albino beavers are rare but have been documented in the wild and captivity. Most North Dakota beavers are medium to dark brown, which provides effective camouflage against tree bark and mud. The underfur is denser and lighter than the longer guard hairs, providing exceptional insulation in cold water and harsh winters.

American Beavers are known for their engineering behavior, they fell trees, build dams, and construct lodges. Watch for freshly cut stumps, often with a distinctive pencil-point or hourglass shape at the base. Their dams can span dozens of feet and create ponds across wetlands. They leave chewed wood debris around active sites, and their scat (droppings) contains wood fiber and plant material. Unlike muskrats, which are common in the same habitats, beavers do not burrow in banks; they build above-ground lodges or den in existing structures. Their track shows five toes on the hind foot and webbing between them, clearly different from muskrat sign.

Beavers are most active and visible during spring and early summer, particularly April through June, when iNaturalist observations peak. They are primarily crepuscular and nocturnal, most active from dusk into the night and again at dawn. During these months, longer daylight and warming water temperatures push them to work on dams and gather food. Winter activity decreases as they rely on cached vegetation under the ice, but they do not hibernate. Fall (September through November) is a secondary period of activity as they prepare winter provisions. Daytime sightings are rare but possible during breeding season or when animals are undisturbed in refuges like J. Clark Salyer or Lostwood.

The muskrat is the only other large rodent in North Dakota waters, but it is much smaller, 2 to 4 pounds compared to the beaver's 40 to 60 pounds. Muskrats have thin, rat-like tails and do not fell large trees or build dams. Their lodge is smaller and less structured than a beaver lodge, built from cattails rather than logs and mud. Nutria, an invasive species, can reach 15 to 20 pounds but lack the paddle tail and large front teeth. Beavers are unmistakable once you see their size, flat tail, and the architectural evidence of their presence. No other North Dakota animal constructs dams or gnaws trees at the beaver's scale.

American Beavers possess continuously growing incisors that are among the most powerful in the rodent world. Their front teeth are covered in hard enamel on the outer surface but softer dentin inside, creating a self-sharpening edge as they chew. Beavers can fell trees up to 6 inches in diameter and occasionally larger trees by gnawing. Their jaw muscles are extremely strong, and their bite force is substantial enough to cut through hardwood. The teeth are orange or yellow-brown due to iron in the enamel, a natural pigment that strengthens them. Unlike human teeth, beaver incisors never stop growing and require constant use to remain at functional length.

American Beavers are non-migratory and remain in North Dakota throughout the year. They establish territories along rivers, streams, and wetlands and maintain the same dams and lodges across seasons. In winter, they rely on cached food, branches stored underwater that they access through holes in the ice. Their dense fur and ability to stay active under ice make year-round presence possible. You may see fewer beavers in winter due to snow coverage and thinner ice, but active sites continue to show fresh gnaw marks and dam maintenance. Spring dispersal of juveniles occurs as young beavers leave natal lodges to establish their own territories, though many remain within the state.

An American Beaver family typically consists of a mated pair and their offspring, totaling 4 to 6 individuals per lodge. Beavers mate for life and remain in family units. Kits born in spring (usually 2 to 4 per litter) remain with parents through their first winter and disperse in spring of their second year. A single dam may create a pond large enough to support one family or multiple families if it is extensive. In North Dakota's productive wetlands, especially in refuges, multiple dam complexes along a stream may indicate separate family territories rather than a single population. Population density varies by habitat quality; rich wetlands support more beavers than marginal sites.