Facts About Beavers
Beavers are among the largest living rodents in the world. They have thick fur, webbed feet and flattened, scale-covered tails. With powerful jaws and strong teeth, they fell trees in order to build homes and dams, often changing their environment in ways few other animals can. In fact, the idioms “busy as a beaver” and “eager beaver” are synonymous with being industrious and hardworking.
There are only two species of beaver. The American beaver (Castor canadensis) typically weighs 60 lbs. (27 kilograms) and are 23 to 39 inches (60 to 100 centimeters) long. The tail adds another 7.75 to 12 inches (20 to 30.5 cm) to its length, according to National Geographic.
Eurasian beavers (Castor fiber) are around the same size. They usually weigh from 29 to 77 lbs. (13 to 35 kg) and are 29 to 53 in (73 to 135 cm) in length, according to the Animal Diversity Web (ADW) at the University of Michigan. Their tails are narrower and skulls are smaller than those of the American beaver.
Beavers have large teeth. Their upper incisors are from 20 to 25 mm long, according to ADW. They continue to grow throughout a beaver’s lifetime. Beavers have adapted to a semi-aquatic existence with closable nostrils and ears, and transparent eye membranes.
Both male and female beavers have a pair of scent glands, called castors, at the base of their tails. They use the secretions from these glands, a musk-like substance called castoreum, to mark territory.
All beavers need water to survive. They live in or around freshwater ponds, lakes, rivers, marshes and swamps. American beavers live throughout North America, but stay clear of deserts and the far northern areas of Canada. Eurasian beavers once lived all over Europe and Asia. Now, they only live in small numbers throughout southern Scandinavia, Germany, France, Poland, and central Russia due to overhunting.
A beaver’s home is called a lodge. Lodges are little dome-shaped houses made from woven sticks, grasses and moss plastered with mud. They that can be up to 8 feet (2.4 m) wide and up to 3 feet (1 m) high inside, according to ADW. Lodges are built on the banks of ponds, on islands or on lake shores, just barely above water level. Many lodges have an underwater backdoor for instant swimming access.
Beavers are primarily nocturnal. They spend most of their time eating and building. Beaver create dams to make ponds, their favorite place to live. Dams are created by weaving branches together, felling trees by cutting them down with their teeth, and waterproofing the construction with mud. Dams can be several meters in length and up to 6.5 feet (2 m) high, according to ADW. Beavers also dig canals to bring water from large bodies of water to their feeding area.
Beavers have a tremendous impact on ecosystems. Dams alter the flow of rivers and can flood hundreds of acres. Dams prevent erosion and raise the water table, which helps purify the water as silt builds up and breaks down toxins, according to ADW. As sediment and debris build up, carbon increases and nitrogen decreases. The chemical changes alter the type of invertebrates, and the new water source attracts new species of birds, fish and amphibians. Flooded timber dies off and a forest becomes an open water ecosystem. Over time, abandoned dams decay, and meadows appear.
Beavers don’t just build homes from trees, they also eat them. Unlike other mammals, beavers can digest cellulose, which is a major component of their diet, according to ADW. Beavers eat leaves, roots and bark from aspens, willows, maples and poplar trees. They also eat aquatic plants.
Beavers are very social and live in groups called colonies. One lodge is often the home for a monogamous couple, their young and the yearlings born the year before.
Beavers mate during the winter, from January to March. The Eurasian beaver has a gestation period of around 60 to 128 days. Then, they give birth to one to six babies that weigh around 8.1 to 22 ounces (230 to 630 grams), according to ADW. Baby beavers are called kits. Eurasian kits are usually weaned after six weeks of life.
American beavers have a gestation period of around 105 to 107 days. They give birth to one to four kits that weigh around 9 to 21 ounces (250 to 600 g). American beavers are usually weaned in around two weeks.
At around 2 years of age, the kits leave the lodge and make one of their own. At 3 years, they find a monogamous mate.
The taxonomy of the beaver, according to the Integrated Taxonomic Information System (ITIS):
Kingdom: Animalia Subkingdom: Bilateria Infrakingdom: Deuterostomia Phylum: Chordata Subphylum: Vertebrata Infraphylum: Gnathostomata Superclass: Tetrapoda Class: Mammalia Subclass: Theria Infraclass: Eutheria Order: Rodentia Suborder: Castorimorpha Family: Castoridae Genus: Castor Species: Castor canadensis (American beaver), Castor fiber (Eurasian beaver)
Beavers were once hunted almost to extinction because they were valued for their pelts, castoreum and meat. Beaver hats were once the height of fashion, and castoreum was used in medicine, food and perfumes.
Today, according to the International Union for Conservation of Nature (IUCN), beavers are not considered endangered. They are widespread, common in many parts of their range, and their populations are stable.
American beaver kits can swim 24 hours after birth.
Beavers have bodies that are made for the water. Their rudder-like tail and webbed feel propel them through the water at 5 mph (8 kph). They can also stay under water for around 15 minutes at a time, according to National Geographic.
Their tails aren’t just used for swimming. Beavers also slap the water with them to startle predators as they dive out of harm’s way.
Beavers do not hibernate. They continue to eat and build throughout the winter.
In the 16th century, the pope decreed that, due to the scaly tail and semi-aquatic lifestyle, beaver could be considered a fish and be eaten during Catholic fasting days, according to ADW.
Castoreum extract has been added to food as a flavor ingredient for at least 80 years, according to a review in the International Journal of Toxicology. According to the Food and Drug Administration, castoreum extract is generally recognized as safe (GRAS). However, because it is difficult to collect, and other flavor enhancer are more readily available, the use of castoreum in food products is rare, and consumption is small — only about 292 lbs. (132 kg) annually, according to “Fenaroli’s Handbook of Flavor Ingredients” (CRC Press, 2004).
Castor oil, a traditional home remedy for constipation, is not made from castoreum, but rather, from the oil of the castor bean.
Beaver, (genus Castor), either of two species of amphibious rodents native to North America, Europe, and Asia. Beavers are the largest rodents in North America and Eurasia and the second largest rodents worldwide. Their bodies extend up to 80 cm (31 inches) long and generally weigh 16–30 kg (35–66 pounds, with the heaviest recorded at more than 85 pounds). They live in streams, rivers, marshes, ponds, and shorelines of large lakes and construct dams of branches, stones, and mud, forming ponds that often cover many hectares. Ecologists often refer to beavers as “ecosystem engineers” because of their ability to alter the landscapes in which they live.
Beavers have short legs and a stout body with a small, broad, and blunt head. Massive chisel-shaped incisor teeth have orange outer enamel because iron has replaced calcium, and this makes them stronger than most rodent incisors. Upon submergence, folds of skin (valves) close the nostrils and the stubby rounded ears, and the eyes are protected by a membrane that keeps water out (nictitating membrane). The fur-lined lips close behind the incisors, blocking water from the mouth and lungs and allowing the animal to cut, peel, and carry branches underwater. Small front feet with five clawed digits dexterously manipulate food. The hind feet are quite large, and the five digits are connected by webbing, which makes them useful as paddles for propulsion underwater. Claws of the second hind digits are split and have serrated edges used for grooming the fur. Fur consists of a grayish to brown layer of short, fine, and dense underfur that keeps water from reaching the skin. Over this layer are long, coarse, glossy guard hairs ranging in colour from yellowish brown through reddish brown to black; underparts of the animal are paler. The distinctive tail is scaly, flat, and paddle-shaped and measures up to 45 cm (about 18 inches) long and 13 cm (5 inches) wide. Both sexes possess castor glands that exude a musky secretion (castoreum), which is deposited on mud or rocks to mark territorial boundaries. Anal glands secrete oil through skin pores to hair roots. From there it is distributed with the front feet and grooming claws over the whole body to keep the fur sleek, oily, and water-repellent.
Beavers are colonial and primarily nocturnal. Their characteristically dome-shaped island lodges are built of branches plastered with mud. In marshes, lakes, and small rivers, beavers may instead construct bank lodges, and in large rivers and lakes they excavate bank dens with an underwater entrance beneath tree roots or overhanging ledges. Each lodge is occupied by an extended family group of up to eight individuals: an adult pair, young of the year (kits), and yearlings from the previous litter. Lodges are usually 3 metres (10 feet) high and 6 metres (20 feet) across the base but can be as large as 5 metres (16 feet) high and 12 metres (39 feet) wide. One or more tunnel entrances open below the water’s surface into a spacious central chamber above water level; the floor is covered with vegetation. An entry tunnel leads to the nest chamber above the waterline. In winter the moist walls freeze, adding insulation and making the lodge impenetrable to predators.
Beavers often construct a dam a short distance downstream from the lodge to deter predators. The dam impedes the flow of the stream and increases the depth of the water that surrounds the lodge. Dams also create additional wetland habitat for fish and waterfowl and contain or impede the downstream movement of oil spilled into rivers. Despite the environmental services these dams provide, land owners and farmers often regard beavers as nuisance animals because beavers sometimes destroy ornamental trees, devour crops, or flood roads and fields with water impounded behind their dams.
During winter beavers store some fat at the base of their tail, but they maintain body temperature primarily by huddling in the insulated lodge and being less active. They leave the lodge only to feed on branches cached beneath the ice. Slow swimmers, beavers can remain submerged for up to 15 minutes and propel themselves primarily with the webbed hind feet while the front feet are held tight against the body. On land they walk or run with a waddling gait. Their diet consists of the soft cambium layer beneath bark, as well as the buds, leaves, and twigs of certain trees (willows and aspens are preferred). Pond vegetation and bankside plants are also eaten. Herbaceous vegetation is consumed mostly during summer and woody matter during winter. Shrubs, saplings, and trees are felled by beavers, cut into portable lengths, and dragged along mud slides or floated through beaver-made canals to the lodge. Edible branches are cached underwater and anchored in mud near the lodge entrance, where they are to be eaten all winter when the beavers cannot break through the ice to cut fresh branches.
Beavers are monogamous, mating between January and March in the north and November or December in the south. One litter per year of one to nine (usually four) kits is born in the spring after a gestation of 105 days. Beavers communicate by postures, vocalization, scent marking, and tail slapping. When alarmed on land, they retreat to water and warn others by slapping the surface of the water with their tails, producing a loud, startling noise. Eagles, large hawks, and most large mammalian carnivores prey on beavers.
American beavers (C. canadensis) occur throughout forested parts of North America to northern Mexico, including the southwestern United States and peninsular Florida. Beavers were at the heart of the fur trade during colonial times and contributed significantly to the westward settlement and development of North America and Canada. As the animal was trapped out in the east, trappers moved progressively westward, and settlers followed. Nearly extirpated by 1900 through excessive trapping for their luxuriant coat, they have reclaimed, either by natural movement or human reintroduction, much of their former natural range, and regulated trapping continues, particularly in Canada. American beavers have been introduced into Finland, where they are flourishing.
Eurasian beavers (C. fiber) were once found throughout temperate and boreal forests of the region (including Britain) except for the Mediterranean area and Japan. By the early 20th century this range had contracted, and at the beginning of the 21st century indigenous populations survived only in the Elbe and Rhône river drainages, southern Norway, France, Mongolia, China, and parts of Russia, especially northwestern Siberia and the Altai region.
Efforts to reestablish the Eurasian species began in Sweden in the early 1920s. Since that time, Eurasian beavers have been reintroduced throughout Europe, western Siberia, western China, Mongolia, the Kamchatka Peninsula, and near the Amur River in the Russian Far East.
Beavers make up the family Castoridae (suborder Sciuromorpha, order Rodentia). With no close living relatives (the mountain beaver belongs to a separate family), modern beavers are remnants of a rich evolutionary history of 24 extinct genera extending back to the Late Eocene Epoch of Asia and the Early Oligocene of Europe and North America. Most were terrestrial burrowers, such as Palaeocastor, which is known by fossils from Late Oligocene–Early Miocene sediments of western Nebraska and eastern Wyoming. They probably lived in upland grasslands in large colonies, excavated extensive burrow systems, and grazed on the surface, their entire lifestyle being much like that of modern prairie dogs. The largest rodent that ever lived in North America was the amphibious giant beaver (Castoroides) of the Pleistocene Epoch. Fossils indicate that it had a body length of two metres and was about the size of a black bear.