Beaver

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Beaver

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 they 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 flavouring.

During the 19th and early 20th century, both species of beaver were decimated due to overhunting, but thankfully a protection law was laid down, which saw the beaver’s population rebound.

Currently, both species are listed on the IUCN Red List as Least Concern. The beaver is known for its building skills and its industriousness and is also the official symbol of Canada.

Table of Contents

Scientific classification

KingdomAnimalia
PhylumChordata
ClassMammalia
OrderRodentia
FamilyCastoridae
SubfamilyCastorinae
GenusCastor

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 functions to keep it warm, protect it against the claws and teeth of predators, and also help it to float in water.

Its guard hairs are 2.0 to 2.4 in (5 to 6 cm) long and generally reddish-brown but 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 moult 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 coloured 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 are known to be able to hold their breath for as long as 15 minutes.

Beavers have dexterous front feet, allowing them to grasp and also manipulate objects as well as 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 manoeuvre 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, which is called a cloaca, and it contains the digestive, genital, and excretory openings.

Behaviour

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 will generally 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 use certain habitats (such as a temporary swamp, a small stream, ditches, and even backyards) temporarily before reaching their final destination.

Infrastructure

Beavers need shrubs and trees as building materials for dams, which impound flowing water, creating a pond for them to live in, and also lodges, which provide protection and shelter.

Construction of lodges and dams begins between late summer and early fall. Beavers can fell trees 5.9 in (15 cm) wide or less in under 50 minutes, while trees as large as 9.8 in (25 cm) can require over 4 hours.

Beavers make trails as they wander on land and these trails can stretch 49 to 59 ft (15 to 18 m). To build a dam, beavers make use of log poles, which are 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, which are the bank lodge and the open-water lodge. The bank lodge consists of holes and tunnels in steep-sloped banks with sticks gotten 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 structures that are 20 ft (6 m) in diameter and 6 ft 7 in (2 m) high.

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 beaver prefer aspen trees.

Both tree species have softwood for peeling and chewing. Beavers do 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 as a means of 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 which 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 take place in the lodge and lasts 30 minutes 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 they are born, 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 also 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 but also copying their parent’s behaviour.

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 times of 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 is a signal for a potential threat, which alerts the whole family.

Distribution

The North American beaver has a wide distribution across the continent down to northern Mexico; being absent only in peninsular Florida, the Arctic, and the deserts of the southwestern US.

In Europe, they are were reduced to isolated populations in the Elbe in Germany, the Rhône of France, the Neman river, southern Norway, the Voronezh River in Russia, and Dnieper Basin in Belarus with a total number of 1,200 individuals.

In 2020, the total number of beavers in Europe was estimated at over 1 million.

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