The American Beaver (Castor canadensis) is a large semi-aquatic rodent native to Canada, much of the United States, parts of northern Mexico, and the most southern province of Argentina, Tierra del Fuego.
Common names include North American Beaver, or simply Beaver in North America, as well as its subspecies names, the most common being the Canadian Beaver.
The american beaver and the European Beaver are the only two animals in the castor genus. However, the American Beaver has several sub-species.
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| Castor canadensis Kuhl, 1820 |
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Beaver Articles Index
American Beaver Description:
The american beaver coat contains two types of hair, and scales. The outer fur, called guard hairs, is coarse and long and covers an undercoat which is much finer. The color varies in individual american beavers, and also tends to vary from location to location, from light nearly blonde fur to a dark brown that is nearly black. The tail is covered with large black scales.
The american beaver has a rounded head, a large flat paddle-shaped tail and webbed hind feet. This is the largest rodent found in North America and the second largest rodent in the world (the South American capybara).
A scent gland near their genitals secretes an oily substance known as castoreum which is used to waterproof the fur. This oil is also deposited by the beaver at selected locations as territorial markers or mating attractants in the spring of the year.
Similar to birds and reptiles, the american beaver has a single lower body opening, known as a cloaca. This single opening serves the urinary and bowel tracts, the secreted oil from the castor glands, and covers the reproductive organs of both male and female beavers.
A thick layer of fat under the american beaver's skin insulates the beaver from its cold water environment.
The eyes are covered by a nictitating membrane which allows the beaver to see underwater. Their nostrils and ears are sealed while submerged. The flat, scaly tail is used to signal danger and also serves as a source of fat storage.
On land, the tail acts as a prop when the beaver is sitting or standing upright. It also serves as a counterbalance and support when the animal is walking on its hind legs while carrying building materials like mud, stones, or branches with its front paws.
The average lifespan of a beaver in the wild is 10 to 20 years, with 12 years being about average. They have lived up to 23.7 years in captivity.
American Beaver SIZE:
An adult american beaver can weigh from 30 - 70 pounds, with 35 - 40 lbs. being average. The american beaver continues to grow in size throughout life, and when food is plentiful all year, they tend to grow larger than usual. Female beavers are as large as males of the same age, and they are sometimes larger.
Adults are 12-24 inches tall at the shoulder and about 25-30 inches long, with an additional 9 to 10 inches making up the tail. The tail is 5 to 6 inches wide and about 1/2 inch thick. They use it for a rudder when swimming, and slap it on the surface of the water to warn of danger.
A beaver's hind legs are longer than its front legs. The hind feet of beaver are fully webbed, and large. These feet often measure 6 inches in length, and the spread of the toes is equal to or greater than the length when spread during swimming. Five toes with strong blunted nails are found on the hind feet, including a unique split toenail on one toe which serves the beaver as a comb for grooming.
The front feet are much smaller, measuring 2 1/2 to 3 inches in length and are not webbed at all. The front claws are tapered and sharp, suited to digging. Beaver normally swim with their front feet held against their chest, and the large webbed hind feet provide the propulsion.
Guard hairs in beaver fur are 2 inches in length, overlaying a soft and dense underfur about an inch deep.
American Beaver COMMUNICATION:
American beavers make a low, groaning sound. They also slap their tails on the surface of water as a danger warning signal. Older beavers will often ignore the tail slaps of younger beavers.
American Beaver POPULATION:
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Before Europeans arrived, there were an estimated 400 million beavers in North America. Between 1853 and 1877, the Hudson's Bay Company, alone, shipped 3 million pelts to Europe.
The beaver existed in ponds, streams and rivers throughout most of North America. Prehistoric Indians used them for fur and food. Images of beaver have been found in the artwork of Hopewell platform pipes.
Historic Indians mainly hunted the american beaver for the meat in their large, flat tails, which tastes similar to pork, and for their pelts. Furs were more valuable to the early European explorers of North America than even gold, and they actively sought out native americans to gather the furs for them. Beaver pelts were one of the most prized furs from the 1600s to the 1800s.
The primary use of beaver pelts by Europeans was in the making of tall, beaver felt hats. After the felt machine was introduced, beaver hats lost their popularity.
From the 1700’s to about 1850, the fur trade (primarily beaver) was the dominant economic activity in Canada and the United States west of the settlement frontier. In fact, most exploration of the North American West was undertaken in search of new furbearer populations and fur transportation routes.
Exploitation of beavers increased with the invention of the steel leghold trap around 1825.
For a long time, beaver pelts were used as money. The cost of a rifle was a pile of beaver skins the same height as the gun. In 1670, Hudson's Bay Company records stated that a beaver pelt would buy: a pound of tobacco, a one-pound kettle, four pounds of shot, or two hatchets.
The Iroquois living in the New York area led the fur trade. They fought other American Indian tribes for prime beaver territory. When the beaver population declined in this area by the middle of the 17th century, the Iroquois moved westward. The intense competition for control of the fur trade between tribes and the French and English was a major cause of the Beaver Wars.
The american beaver also has strong musk glands which produce castoreum, used in making perfumes yet today.
By 1890, there were only isolated pockets of american beavers left in the wilds of North America. The beaver received protected status in the US by around 1900, but it was nearly sixty years before the american beaver population began to increase again with reintroduction programs put in place in the 1950s, When it did begin to recover in ernest in the early 1970s, the population increased rapidly. Today, there is again regulated trapping of beavers allowed.
In 1984, there were roughly 2 million beaver in the United States, and the total North American population was estimated at between 6 and 12 million in 1991.
American Beaver RANGE:
The American Beaver (Castor canadensis) is native to Alaska and Canada south of the Arctic Circle (including Vancouver and Newfoundland), most of the continental United States (absent from parts of southwestern USA and from most of Florida), extending into New Mexico. It was introduced to Tierra del Fuego (South America) and Eurasia, including Finland, northwestern Russia, Poland, Germany, and Austria.
Beavers are absent from the tundra of northern Alaska and Canada, parts of the Midwest, much of South Carolina, and peninsular Florida. In arid regions of the southwestern United States, beavers only occur along larger streams and rivers.
The North American beaver has been successfully introduced to southern South America and to Europe, where Castor canadensis now outnumbers the native C. fiber in some areas.
Adult beaver mark out their territories in early spring by dragging up mud and debris from the bottom and depositing the debris in mounds along the shores, where they also deposit oil from their castor glands. These "castor mounds" often leave a reddish stain on the bank, and the odors are powerful enough for a human to easily detect.
Once the american beaver has selected a territory, it is very hard to persuade them to leave. Because of this trait, and their propensity for building dams, they can become a nuisance animal when their territory intersects with that of humans.
Generations of beaver will continuously inhabit a choice area, even building canals to help float food from inland cutting sites. If and when food supplies are exhausted, they do relocate to better area. Young beaver also disperse to find their own territories, since territories seldom overlap. But if an older beaver pair dies off, other beaver in the nearby areas will move in if it's better than the territory they already claim.
The average american beaver territory covers several miles.
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American Beaver BEHAVIOR:
Besides man, the beaver is one of the few animals that can change their environment to benefit themselves.
They are master dam builders, pooling deep water behind dams that are typically four or five feet high.
Occasionally dams exceed three hundred feet long, and one record dam in Montana was 2,140 feet long. Beaver carry branches in their teeth or wedged between their front legs and chest. They also carry mud between their front feet and chest. The branches and mud are wedged into any area where water flows until a solid dam is completed.
American Beavers are nocturnal, which means they are mainly active at night. They do sometimes come out in daylight, and are usually seen near dusk. They are excellent swimmers but are more vulnerable on land and tend to remain in the water as much as possible. Although beaver normally submerge for 3 or 4 minutes at a time, they are quite capable of holding their breath for 12 to 15 minutes. They exhale a little in spurts as they swim or work under water, and a large beaver is quite capable of traveling nearly 1/2 mile under the surface before it must surface for more air.
Permanent homes called lodges are constructed by piling up layers of sticks into a large conical pile above the waterline. Two or more underwater tunnels are then chewed up into the pile, and an inner chamber is hollowed out to serve as a living quarters. Finally the outside of the lodge is plastered with mud and rocks, except for the peak, which is left porous enough to allow an air exchange to the inner chamber.
There are two levels to the chamber. One level is near the waterline near the "plunge holes", where the beaver shed water before climbing to the higher resting or nesting areas.
Beavers build dams to slow down the flow of water in streams and rivers and then build stable lodges for shelter. The dams are engineered according to the speed of the water; in slow water the dam is built straight, but in fast water the dam is built with a curve in it. This provides stability so that the dam will not be washed away.
In areas prone to flooding, or where strong currents may be present, beaver will sometimes build bank dens by digging tunnels from under the waterline up into the banks. Bank dens will usually have two or more submerged entrances.
Many times the beaver will construct a pile of sticks over the tops of the underground living chambers. These piles of sticks are sometimes called "caps".Shallow pockets are sometimes dug into banks near the waterline and these are known as "feed pockets".
In northern areas, the american beaver constructs "feed piles" by submerging large amounts of small trees and limbs to serve as a food source after ice prevents them from activity above the ice. These feed piles are usually constructed close to the den as a convenience to the kit beaver, who do not normally travel far from the den itself.
The american beaver is territorial, and usually lives in family groups called "colonies" that can reach 25-30 individuals, but are usually smaller, around eight animals. The colony usually consists of a breeding pair, their offspring of the current year, and offspring from the previous 22 months. Older sibblings helping with infant care, food collection, and dam building. The colony will fiercely defend it's territory from other beaver families.
When a kit is about 22 months old, they are chased off to find their own mate and territory just before a new litter is born.
However, there are also instances of an american beaver living alone. These are known as "bachelors," whether they are male or fernale. These are usually young beavers looking for a mate and a new territory.
American Beaver FEEDING HABITS:
Beaver are primarily vegetarians although an occasional beaver may eat a dead fish. Preferred foods include the bark of aspen, willow, cottonwood, and dogwood, and many other varieties of trees and shrubs.
Beaver skulls and teeth are disproportionately large. This is crucial for cutting through hard woods like maple and oak. Most noteably, the upper incisors, bright orange in color, are at least 5 mm wide and 20-25 mm long.
All beavers have two upper and two lower incisor teeth, which dominate the front of a beaver's mouth. The upper incisors overlap the lower incisors, and friction from chewing causes the teeth to self-sharpen. These teeth are unique because they continue to grow all their lives, so if they did not chew and wear them down, they would eventually become so long they would kill the beaver.
In early spring, beaver will often eat bark and twigs of evergreens. In season, beaver will also eat water lillies (one of their favorite foods), leaves, grassses, roots, and a variety of crops including corn, wheat, oats, carrots, potatoes, apples, clovers, and alfalfa.
American Beaver BREEDING HABITS:
Male and female beavers are sexually mature at about 3 years of age. They are usually monogamous, but will take a new mate if the old one dies. The american beaver breeds once a year, usually in January or February. They have one litter per year, with litter sizes varying from 1-8 kits. The average litter size is 3 to 4. Baby beaver are called kits.
After a gestation period of 107 days, the adult male and kits from the previous year usually take up a temporary residence in a bank den while the new litter is being born in April, May or June. The delivery of the litter can take several days.
At birth kits are usually around 38 cm long including their tales. They tend to weigh from 250 to 600 grams and can be red, brown, or almost black. They remain in the lodge for a month, afterwards leaving for longer periods of time to swim and take in solid foods. Most beavers are weaned within two weeks, although it can take up to 90 days.
In preparation for birth females will prepare a soft bed within the lodge. She then will use her flat tail as a sort of birthing mat. She will lick each kit clean, and nurse it. Both mother and father beaver play a part in providing food for the young and protecting them from predators.
Beaver kits are fully furred when born, their eyes are open, the incisor teeth are visable, and they will take their first swim within hours of birth.
American Beaver Ecosystem Roles
Beavers maintain wetlands that can slow the flow of floodwaters. They prevent erosion, and they raise the water table, which acts as a purifying system for the water. This happens because silt occurs upstream from dams, and toxins are then broken down. As ponds grow from water backed up by the dam, pond weeds and lilies take over. After beavers leave their homes, the dams decay, and meadows appear.
THREATS TO the American Beaver:
American beaver predators include mountain lions, wolves, northern river otters, fishers, lynx and bobcats. Occasionally, a bear or wolverine will kill a mature beaver, but they are not a common threat. Usually an adult beaver's size is a deterrent to most predators. Juvenile beaver are very vulnerable to many predators, especially coyotes, eagles, and large owls. The most common beaver predators are humans, wolves, and coyotes.
Killing beavers for their pelts, disrupting them through encroachment and changes in habitat, and slowly poisoning them through pollution, which is known to infect wounds, all have lead to man becoming a major threat to the beaver species.
Tularemia can be a devastating disease for the american beaver, wiping out entire populations when conditions are favorable. Tularemia infects the liver, and is usually fatal to beaver of all ages.
Beaver are also host to an internal parasite called giardiasis. Water inhabited by beavers can become contaminated by the giardiasis cysts, which are too small to be filtered out of the drinikng water. These cysts hatch in the small intestines of people who drink the contaminated water resulting in diarrhea, nausea, and stomach aches.
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American Beaver TRIVIA:
The beaver is one of Canada's national symbols and appears on one of their 5 cent coins. It also appeared on the first Canadian postage stamp. Since then, the beaver has appeared on seven Canadian stamps.
On March 24, 1975, the beaver received the highest honour ever bestowed on a rodent. On that day it became an official emblem of Canada when an "act to provide for the recognition of the beaver (castor canadensis) as a symbol of the sovereignty of Canada" received Royal assent.
The 1976 Summer Olympics in Montreal had Amik the beaver as their mascot. The name Amik means beaver in the Algonquin language.
Canadians have celebrated National Beaver Day on the last Friday in February since 1974.
A relative to the american beaver, the Giant Beaver, Castoroides ohioensis, lived in North America during the Ice Age. The giant beaver reached lengths up to seven and a half feet and weighed up to 700 pounds, but became extinct about 10,000 years ago.
A beaver family can fall as many as 300 trees in a single winter. A pair of beavers can gnaw through a four-inch-thick branch in 15 minutes.
Scouts Canada (Boy Scouts) includes the Beaver Program in their organization. It consists of a group of Beavers 5 to 7 years of age. Beavers meet in a group called a colony. The colony is split into smaller groups called lodges. There is one leader for every five Beavers. Each Beaver learns a promise, law and motto to help guide their personal development.
The Beaver is the state animal of the State of Oregon and the State of New York.
To dream of seeing beavers, foretells that you will obtain comfortable circumstances by patient striving. If you dream of killing them for their skins, you will be accused of fraud and improper conduct toward the innocent.
