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Scientific Name: Castor canadensis

New York Status: Not Listed
Federal Status: Not Listed


BeaverThe beaver is New York State's official mammal. It is unmistakable due to its large body size (26-65 pounds, 25-35 inches) and broad flattened tail (9-10 inches long, 6 inches wide), not to mention the characteristically altered habitat in which it resides.

A unique feature of the beaver is a second set of eyelids. The secondary eyelids, known as a nictitating membrane, are white and form an inner eyelid. Additionally, their ears and nose can close while underwater! Beavers have lips that close behind the incisors which allow them to gnaw underwater. These large incisors are continuously growing and are kept at a manageable length by the gnawing action beaver use to gather food. Their rich, dense fur ranges in color from yellow-brown to almost black. Webbed hind feet serve to compliment the extraordinary swimming ability of the beaver. The second hind toe has a split nail, which appears to aid in grooming.

The beaver's tail is flat, which helps them swim throughout aquatic habitats. It serves other purposes as well. The tissue beneath the scaly outer layer, which is actually compressed, grouped hairs, contains many blood vessels at its base. It serves as a thermoregulatory tool (helps them to maintain a consistent body temperature). Blood flows from the surface of the tail, thereby minimizing heat loss. It also assists in fat storage.


Beaver rarely leave the water for long periods of time. They can be found in wooded streams; the margins of lakes, ponds, and reservoirs; swamps and marshes; and many other sources of year-round water. Ideally, waterways will be of low gradient with an abundance of aspen, willow, or alder, as well as a variety of aquatic vegetation.

Food and Feeding

The beaver's diet consists almost entirely of cellulose in the form of woody plant material. Woody plants are nearly indigestible to mammals. Digestion is aided by microorganisms inhabiting the small intestine. Beavers eat the leaves, bark and twigs of trees such as aspen, willow, and red maple and a variety of herbaceous plants. During summer months, their dietary preferences may shift to aquatic vegetation including water lilies and rhizomes from shoreline ferns.

As winter draws near, beaver may collect and store food items, called a raft'or feedpile, underwater near the entrance to their lodge to use throughout the winter. This food store is imperative for survival when thick ice prevents access to fresh food during New York's long winters.


Reproduction in beaver leads to the formation of their basic social unit, the family or colony. Beaver mate for life, but if one member of a pair dies, the remaining member will readily accept a new mate. These colonies usually consist of the parents, the present year's offspring, and often times there will be a representative from the previous year's litter. Infrequently an 'extra' adult will be found within a colony. As a colony grows, members may undoubtedly expand their breeding and foraging territories, building dams and lodges to support shelter requirements and expand home ranges. A typical number of beaver per colony is between four and six, but up to a dozen is possible.

Home ranges or colonial territories are established and passively defended by means of scent-mounding. This is where an adult beaver piles up muddy debris and marks the top with castoreum, which is washed out of the castor glands with urine. Active defense includes potentially violent encounters. Many beaver have been shown to bear the scars of territorial disputes. Such encounters seldom end in death.

Other forms of communication include vocalizations, postures, and tail-slapping. Tail-slapping is thought to be a means for one beaver in a colony to warn other beaver of a potential threat. Another function may be to frighten would-be predators away.


Like most rodents, beaver construct an elaborate den or lodge with multiple entrances. Beaver differ from other rodents not only in size, but the fact that beaver alter their surroundings to suit their needs. Possessing the unique ability to fell trees, they use this talent to not only get food. It is also a source of construction material for their lodges and the watertight dams they build to impound the area that they intend to inhabit. They are cued to begin construction at the sound and motion of running water. Beaver impound an area not only for a place to live and rear their young, but it also adds protection from certain predators.

Depending upon the type of habitat they colonize, they may create a home in a stream bank, or a lodge out in open water. These have two or more underwater entrances and the 'living quarters' of their lodge will be above the level of the surrounding water. In the wintertime, it will maintain a temperature significantly higher than that of the surrounding air.

Dubbed "nature's finest wetland engineer", beaver activity has both disruptive and beneficial impacts on any body of water they colonize. Beaver impound a variety of wetland types and streams with different forest types and gradients. This colonization converts the existing habitat to open water and provides a valuable resource for a variety of furbearer and waterfowl species. However, it can eliminate the existing natural diversity of certain groups of organisms, such as reptiles and some fish species, that may require cooler water than is provided by a beaver impoundment. Flooding of surrounding landscapes can prevent natural succession. It may destroy actual forest stands of trees not adapted for prolonged submersion of their roots.

Their dam-building activity can cause widespread flooding of forest and agricultural lands. Nuisance complaints regarding beaver activity are widespread across New York State. Flooding not only has the potential to change the ecology of a colonized area, but it can also cause hazards to human habitation by plugging culverts and flooding roads, railroad tracks, and agricultural lands. There are also general property damage concerns.


Beaver reproduce once a year and form lifelong breeding pairs. Breeding occurs in January or February and young are born in May or June after an average gestation time of 107 days. Litter size may range from 2 to 7 kits. The number of offspring could be based on the quantity and quality of available food and habitat in any given year.

Kits are born with fur, with teeth that are erupted, and eyes that are open. They may enter the water within a few hours following birth. For the first few weeks of life, a kit's fur is not water-repellent. Their anal glands, which beaver use to grease up their fur, are not functional until the third or fourth week of life.

Predators, Parasites, and Diseases

Beaver are more susceptible to predation by animals such as coyote, fisher, bear, and bobcat when traveling extended distances from water in search of food. Kits may fall prey to mink, otter, fox, and great-horned owls. Studies in the Adirondack Park suggest that beaver are heavily relied upon by coyotes, and rank second to white-tailed deer as a preferred food source. Humans are one of the major sources of beaver mortality through trapping and automobile collisions.

Beaver harbor a variety of parasites, both internal and external. Internally, they have different varieties of nematode, a form of intestinal roundworm, in different parts of the intestinal tracts. There are also cestodes or tapeworms that inhabit large portions of the small intestine, and apparently cause little to no harm to the host. Giardia lambdia is a two-celled flagellate that inhabits parts of the intestines and causes beaver fever in humans. It is known to be found in close association with the beaver but has not been identified as the definitive host of this rather uncomfortable parasite. For more information, visit the New York State Department of Health website to view a fact sheet (leaves DEC website) on beaver and giardiasis.

Externally, beaver can have multiple species of mite that dwell in their dense fur. There can be as many as 10 species of mite living on a single beaver. Each species is specialized for life in a distinct part of the animal's body. For instance, the mites living around the head are not the same species of mite that one would find in the hindquarters.

Watchable Wildlife

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When looking for wildlife in New York, visit the Watchable Wildlife webpage for the best locations for finding your favorite mammal, bird, reptile, or insect. New York State has millions of acres of State Parks, forests and wildlife management areas that are home to hundreds of wildlife species, and all are open to the public. Choose from hundreds of trails and miles of rivers as well as marshes and wetlands.   

Remember when viewing wildlife:  

  • Don't feed wildlife and leave wild baby animals where you find them.  
  • Keep quiet, move slowly and be patient. Allow time for animals to enter the area.  

Quick Facts About Beaver

  • A beaver can chew down hundreds of trees each year and a family of beavers can eat up to a ton of bark in a winter.
  • With waterproof fur, webbed hind feet, and the ability to hold its breath for 15 minutes, the beaver is well adapted to life in the water.
  • Beaver have prominent orange teeth, dark brown fur, and a flat, paddle-shaped tail

Where to Watch

  • Streams, rivers, or ponds bordered by woodlands or small marshes.
  • Near active beaver dams - look for the lodge, a dome-shaped structure 5-6 feet tall and 20-30 feet wide.
  • Look for tree cuttings and "chips" of wood near the shoreline.

What to Listen for

  • Tail slaps on the water.

When to Watch

Beavers are active year-round and most likely to be seen early in the morning or at dusk. You may also see one at night with moonlight. In the winter, look for large holes in the ice on ponds that the beavers use to access the underwater entrance to their lodge. Approach carefully and stay hidden--beaver are shy. Be patient-it may take a long time before you finally see a beaver.

The Best Places to Watch

Return to the Watchable Wildlife main page