Beaver-like Mammals of New York

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Large Semi-Aquatic Rodents of New York

None of the Beaver-like mammals listed here are closely related species, but are all members of the rodent (Rodentia) order of animals. Their appearance, semi-aquatic habitat and foraging habits are very similar, so we group them together based on what you may perceive an animal to be. You can then read the details and try to narrow it down to a particular species.

Interesting Facts about the American Beaver:

  • Despite what you may have seen in children’s books or cartoons, the beaver’s tail is not used to construct the dam. It’s an adaptation for better control while swimming.

  • Second only to humans, beavers are the only animals to single-handedly manipulate their surrounding environment. The wetlands and artificial lakes created by beavers are beneficial to the environment in the long run. Parking lots are not. 

  • Beavers don’t need to build a dam. If they find a pond or lake suitable enough, they will be content building just a lodge.

  • Beavers can close their nostrils and their ears underwater. Their incisors protrude past their lips allowing them to chew wood underwater without getting water in their mouths.

  • Beavers don’t need to build dams. If a constant 2-4 feet of flowing fresh water is available, and they have enough wood for food, they’re happy. 

  • As beavers continuously feed, stockpile and construct with the surrounding timber, they need to continuously build up their dam and extend the lake to safely access new trees.

Beaver Books and Field Guides

Identification Guide for Beaver-like Animals of New York

American BeaverAmerican Beaver

Beaver Lodge

Beaver Lodge

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American Beaver
(Castor canadensis)

AKA: Beaver, Woodchuck (incorrectly)

Identifying characteristics: A large aquatic rodent with varying degrees of dark brown fur. The fur is naturally thick and oily, due to its waterproof nature. The ears and eyes are small, dark and round and the nostrils are large and closable. The incisors are large and orange. The hind feet are fully webbed and the front feet are not webbed, are smaller and clawed. Due to the hind legs being longer than the front legs, the Beaver’s body profile slants down towards the head. The beaver is easy to identify by the tail alone (if you are lucky enough to see it above water). The scaly black tail is large, very broad and flat.

Size: The largest rodent in North America, they can be 3-4 feet in length and weigh from 30 to 70 lbs.

Habitat: Aquatic. Lakes, streams and ponds (either natural or created by the beaver’s dam), with an average depth of 4 feet, within wooded areas. The beaver lives within a lodge, built near shore or on a small island, made of sticks, mud, grass and moss. A lodge will always be in contact with water, but for the most part is above the surface. They are usually furnished with bark, grasses and wood chips. Two underwater entrances offer an option for escape when a predator attacks the lodge. Beavers will constantly build upon and repair their lodges and dams.

Food: Herbivore. Bark and cambium (soft wood under the bark). They prefer birch, aspen, willow and poplar. They will store large quantities of sticks underwater for winter feeding. The young especially will feed upon aquatic plant, such as water lilies.

Vocalization: Low groaning sounds, whines. Will slap their tails against the water, producing a clapping noise, to warn others of threats.

Predators: Humans. Bears, fishers and otters are a threat to juveniles (kits).

Reproduction: Beavers are monogamous. Litter size average 2 with only 1 litter a year. Kits will stay with their families and help around the lodge for 2 years. Mating season is in the winter (Jan-Feb).

Other Info.: Primarily nocturnal and family oriented. They will often live in families of 4-8, with younger siblings helping to raise the kits. Since they are more agile in water than on land, they will often build small canals to provide access to quality food sources. They are superb swimmers, but clumsy on land.

Distribution

Complete distribution

Found near bodies of water throughout the state, surrounding states and most of North America.

Status: none

Tracks

Castor canadensis  tracks

Look for tracks often in mud (due to their close proximity to water) with 5 inch long, webbed hind feet and smaller, 3 inch long, unwebbed fore prints. A fore print will generally be side by side with a hind print. Beavers also tend to drag their tails through their prints.

MuskratMuskratFind more images

Muskrat
(Ondatra zibethicus)

AKA: Swamp bunny

Identifying characteristics: They look like small beavers at first glance, with with similar brown, glossy fur and robust body. But are considerably smaller and have a few other characteristics to help you distinguish them from beavers. The ears of a muskrat are so small, they are barely noticeable. Also the legs (both front and back) are short and stubby, with only minor webbing on the hind feet. More notably, the tail is not as broad and flattened like the beavers, it is more similar to the rat’s; hence the name.

Size: From 12 to 24 inches in length and weighing an average of 2.5 lbs.

Habitat: Aquatic. Swamps, marshes and ponds with abundant aquatic vegetation and average depths of 5 ft. Marshes are preferred as they offer consistent water levels and abundant vegetation. Nests can either be burrows into the bank, or “houses” built in shallow water by piling vegetation and mud on a solid object (such as a stump). The immediate area surrounding a nest is generally cleared of plants.

Food: Omnivore. Primarily green vegetation (aquatic plants, such as cattails, lilies and loosestrife), roots, crops. Sometimes will feed on mussels, crayfish or carrion, if available.

Vocalization: Mating season may bring about squeaks, grunts and barks.

Predators: Humans (for pelts), minks, fishers, birds of prey.

Reproduction: Litter size average 6 (sometimes reaching 18) with up to 3 litters per mating season. Young will go on their own after 30 days. Mating season is generally around March-August.

Other Info.: Primarily nocturnal, but often active during the day. They are excellent swimmers and can stay underwater for up to 17 minutes at a time, but they are clumsy on land. They live in large family groups, but are very territorial. They use strong scent markings to mark their territory (hence Muskrat). Despite the name, they are not rats at all.

Distribution

Complete distribution

Found in wetlands across the sate and neighboring states.

Status: none

Tracks

Muskrat tracks

Look for tracks often in mud (due to their close proximity to water) with 2-3 inch long hind prints and smaller 1 inch long fore prints. Hind prints will generally not show any webbing and will fall slightly within the preceding fore print. Fore prints may also appear to be 4-toed as the 5th toes is so small, it may not form on the print.  Muskrats also tend to drag their tails through their prints.

NutriaNutriaNutriaFind more images

Nutria
(Myocastor coypus)

AKA: Coypu

Identifying characteristics: This aquatic rodent may remind you of a large, chunky rat. Its incisors are a striking bright orange. Like other aquatic rodents, the eyes and ears of the Nutria are small, the nostrils are large, and the fur is thick and oily. The coat ranges from a dark to light reddish brown. The fur around the mouth and snout is usually frosted. The tails are long and scaly, like a rats, and are not dorsalaterally flattened to any degree like the beaver’s or muskrat’s – they are completely round. The hind feet have 5 toes with 4 of them webbed. The fore feet have 4 toes and a small vestigial thumb. Females have nipples along the sides of their back, which helps them feed their young while in water.

Size: From 18 to 23 inches in length and weighing from 11 to 22 pounds.

Habitat: Semi-aquatic. Marshes, lake or pond shores, slow moving streams or lagoons. Plenty of green aquatic vegetation required. Not tolerant of extreme cold. They will usually construct feeding platforms out of floating vegetation. Burrows are tunnels along the shore.

Food: Herbivore. Aquatic vegetation. Some crops. Nutrias often feed while in the water, but when aquatic vegetation is scarce, they are comfortable on land and will seek out other sources of food, like cabbage or carrot crops.

Vocalization: Not known.

Predators: Birds of prey, minks, fishers.

Reproduction: Litter sizes average 6, with more than 1 litter per year. There are no specific seasons for mating. Young stay with the mother for up to 2 months.

Other Info.: Nutrias are native to South America and were introduced here by the fur industry. Accidental releases have led to some small populations in NY State. Nutrias are a threat to wetland habitats as they can uproot and devour large quantities of plant life. They are known to completely destroy marshland. Once natural vegetation is depleted, they become a pest to nearby farmers.

Distribution

Unknown / Undetermined distribution

Although specific population locations are not known, this invasive species was released accidentally from fur farms in NY State or neighboring states and may be present in some wetland areas.

Status: Invasive!
Contact your regional DEC
office for assistance.

Tracks

Nutria tracks

Look for large, partially webbed hind feet with a peculiar thumb pointing to the outside and smaller 4-clawed fore prints.

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