Beavers are regarded as large, semiaquatic rodents native to the temperate Northern Hemisphere.
There are two still living species in the genus Castor, the Eurasian beaver (Castor fiber) and the North American beaver (Castor Canadensis). Beavers are known as the second-largest living rodents.
They have long chisel-like incisors, stout bodies with large heads, grey or brown fur, scaly tails, hand-like front feet, and webbed back feet.
The North American beaver is said to have a broader tail and larger skull than the Eurasian beaver.
Beavers can be found in several freshwater habitats, such as rivers, streams, ponds, and lakes.
They are herbivorous animals and consume aquatic plants, tree bark, grasses, brush, and sedges.
Beavers build lodges and dams using tree branches, rocks, vegetation, and mud. Lodges serve as shelters, whereas dams impound water.
Beavers are classified as keystone species because their infrastructure creates wetlands used by other species and also for their effect on other organisms in the ecosystem.
They live in monogamous pairs with their young. When the parent becomes old, the young will help repair the lodges and dams and may also help raise the newly-born young.
Beavers are highly territorial and mark their territories using scent mounts made of debris, mud, and castoreum (a urine-based substance excreted through their castor sacs).
Historically, poachers have hunted beavers for their meat, fur, and castoreum.
Castoreum has been used in perfume, medicine, and food flavoring.
During the 19th and early 20th centuries, both species of beaver were decimated due to overhunting, but thankfully, a protection law was laid down, which saw the beaver’s population rebound.
Both species are listed on the IUCN Red List as Least Concern.
The beaver is known for its building skills and perseverance and is also the official symbol of Canada.
Scientific classification
| Kingdom | Animalia |
| Phylum | Chordata |
| Class | Mammalia |
| Order | Rodentia |
| Family | Castoridae |
| Subfamily | Castorinae |
| Genus | Castor |
Species
- Eurasian beaver (Castor fiber)
- North American (Castor canadensis)
Characteristics
Beavers have a head-and-body length of 31 to 47 in (80 to 120 cm), with a 9.8 to 19.7 in (25 to 50 cm) tail, a shoulder height of 12 to 24 in (30 to 60 ft), and a weight of 24 to 66 lb (11 to 30 kg). Both sexes are almost identical externally.
A beaver coat has 12,000 to 23,000 hairs/cm3 and keeps it warm, protects it against predators’ claws and teeth, and helps it float in water.
Its guard hairs are 2.0 to 2.4 inches (5 to 6 cm) long and generally reddish-brown, but they can range from nearly black to yellowish-brown.
The underfur is 0.79 to 1.18 in (2 to 3 cm) long and dark grey. Beavers are known to molt during the summer.
Beavers possess massive skulls adapted for withstanding the biting forces generated by their powerful chewing muscles. Their 4 incisors grow continuously and are chisel-shaped.
The outer enamel of the incisors is colored orange (due to the presence of iron compounds) and is very thick.
Beavers have 2 premolars and six molars on each side, which makes up 20 teeth in total (plus 4 incisors).
The beaver’s ears, eyes, and nostrils are arranged so that its head can stay afloat while the body stays submerged.
Beavers usually spend 5 – 6 minutes underwater per dive and can hold their breath for as long as 15 minutes.
Beavers have dexterous front feet, allowing them to grasp, manipulate objects, groom, and dig.
The hind feet are larger than the forefeet and also have webbing between the toes.
A beaver is capable of carrying objects while walking on its hind feet. The most distinctive part of the beaver is its flat, scaly tail, which it uses to maneuver underwater.
A beaver’s tail has a countercurrent blood vessel system and also stores fat.
Both the male and female beaver have their sex organs located inside their body, with the male having a bone in its penis.
They possess just one opening, called a cloaca, containing the digestive, genital, and excretory openings.
Behavior
Beavers live in freshwater ecosystems like streams, rivers, ponds, and lakes.
One of the most important parts of beaver habitat is water, and they require a year-round supply for diving, swimming, protection of lodge entrances, floating logs, and safety from land-dwelling predators.
They prefer wide, slow streams. Beavers may abandon a location for years after a flood or avoid areas with regular flooding.
They are primarily nocturnal and spend most of the daytime in their shelter.
Beavers prefer areas with diverse vegetation close to the water and flatter terrain.
North American beavers are found in areas where trees are around 200 ft (60 m) from the water.
Dispersing beavers will temporarily use certain habitats (such as a temporary swamp, a small stream, ditches, and even backyards) before reaching their final destination.
Infrastructure
Beavers need shrubs and trees to build dams, which impound flowing water, creating a pond for them to live in, and lodges, which provide protection and shelter.
Construction of lodges and dams begins between late summer and early fall.
Beavers can fall trees 5.9 in (15 cm) wide or less in under 50 minutes, while trees as large as 9.8 in (25 cm) require over 4 hours.
Beavers make trails as they wander on land, stretching 49 to 59 ft (15 to 18 m).
To build a dam, beavers use log poles, around 6 ft 7 in (2 m) long and 2.0 in (5 cm) in diameter, to brace against the banks.
Dams can be as low as 8 in (20 cm) to as high as 10 ft (3 m) tall and can stretch 1 ft 0 in (0.3 m) to several hundred meters long.
Beavers build two types of lodges: the bank lodge and the open-water lodge.
The bank lodge consists of holes and tunnels in steep-sloped banks with sticks from fallen trees piled over them.
The open-water lodges, which are more complex, are built over a platform in shallow water using mud and sturdy logs. Lodges built by novice beavers are usually small and sloppy.
More experienced beavers can build 20 ft (6 m) in diameter and 6 ft 7 in (2 m) high structures.
Diet
Beavers have a generalist and a herbivorous diet. They primarily eat tree bark during the fall and winter; Eurasian beavers prefer willow trees, whereas North American beavers prefer aspen trees.
Both tree species have softwood for peeling and chewing. Beavers harvest other tree species like alders, maples, beech, cherry, and hornbeam.
Non-woody plants make up more of their diet in the summer and spring and include aquatic plants like raspberries, water-shields and lilies, ferns, sedges, and grasses.
The average lifespan of a beaver is 10 years. Its predators include coyotes, wolves, lynxes, foxes, bears, and cougars.
Beavers use the water to escape when they feel threatened on land.
They host some parasites, which include the protozoan Giardia duodenalis which causes beaver fever or giardiasis. The bacteria Francisella tularensis causes tularemia and the beaver mites and beetles of the genus Schizocarpus.
Reproduction
A beaver’s family can have up to 10 members. Female beavers have their first estrus cycle of the season between late December and mid-January.
They may enter estrus 2 to 4 times per season; each cycle lasts 12 to 24 hours.
Mating usually occurs in water but may also occur in the lodge and lasts 30 to 3 minutes.
The gestation period lasts 104 – 111 days, with 3 or 4 kits or young being born. Newborn beavers are fully furred and precocial.
Both parents take part in raising the offspring. After birth, the young spend most of their first month inside the lodge; their father maintains the territory while their mother is the primary caretaker.
When they finally leave the lodge, they will help their parents repair the dams and lodges and build food caches in the fall.
Young beavers depend on their parents for food and also to teach them life skills.
They spend most of their time playing with each other and copying their parent’s behavior.
The offspring are weaned at ten weeks old. They leave their parent’s territory at 1 or 3 years of age.
They may also remain with their parents during high population density, food shortage, or drought.
Within the lodge, they communicate with whines and burps. They also produce bubbles and gargles when entering and exiting.
The slapping of water with its tail signals a potential threat, which alerts the whole family.
Distribution
The North American beaver is widely distributed across the continent down to northern Mexico, absent only in peninsular Florida, the Arctic, and the deserts of the southwestern US.
In Europe, they were reduced to isolated populations in the Elbe in Germany, the Rhône of France, the Neman River in southern Norway, the Voronezh River in Russia, and the Dnieper Basin in Belarus, with 1,200 individuals.
In 2020, Europe’s total number of beavers was estimated at over 1 million.
