Different Types of Beavers

Beavers are semi-aquatic rodents of the Castoridae family. They are characterized by their thick fur which is waterproof, something useful for their semi-aquatic behaviors. They need to live near a body of water, but they will also spend time on land. Another useful adaptation is their flat tail which resembles a paddle. Instead of fur, it is covered in scales and they contain a large amount of adipose tissue (fat).

As they need to swim a lot, a beaver's tail is helpful in navigating in the water. It is used for steering and balancing more than propulsion. This tail also helps them to balance on land, especially if they are carrying heavy loads. This is something they do when building their dams, something with which this rodent is often associated.

While there were various types of beaver in the Castoridae family, there are now only two living species in the world. They are the following:

• North American beaver (Castor canadensis)
• Eurasian beaver (Castor fiber)

The Kellogg's beaver (Castor californicus) lived between the Miocene and Pleistocene periods in western North America. It is now sadly extinct. Extant beavers live exclusively in the Northern Hemisphere, with the exception of some populations that have been introduced in Argentina and Chile where they have become invasive alien species.

Although C. canadensis and C. fiber are very similar, they have several differences. This includes their genetic history, as reflected in their differences in chromosome number. We look more at each beaver species individually to learn more about their similarities and differences.

We start by taking a look at the different physical and behavioral characteristics of the North American beaver (Castor canadensis) depicted in the photo below:

• Distribution: perhaps unsurprisingly, the North American beaver is found throughout North America. Its population ranges as far south as northern Mexico and extends to most of the United States and Canada. Exceptions include the Arctic tundra, Florida peninsula and deserts of the southwestern United States. It has been deliberately introduced to Finland, certain regions of Russia and Tierra del Fuego in Argentina. It has also spread to some islands in Chile, where it has become an invasive alien species and a threat to ecosystem conservation.
• Habitat: inhabits areas near lakes, ponds and streams with access to adequate food and building resources. It lives in burrows on the banks of rivers and lakes. Their burrows measure about 4 m in diameter and 1.5 m in height, always above the water level.
• Behavior: the North American beaver can build dams to retain water, create food reserves, provide safe shelter and facilitate the transport of woody material. Food reserves are especially important when terrestrial vegetation is difficult to access. It is both a nocturnal and gregarious mammal. You can learn more about another gregarious rodent with our article providing fun facts about the capybara.
• Size and weight: it is considered the largest rodent in North America, reaching 70 to 80 centimeters in length and weighing up to 32 kilograms. Its body is robust and muscular.
• Coat: it has a waterproof, dark reddish-brown coat that has the ability to prevent water from entering the body when it is in aquatic environments.
• Diet: it is a herbivorous animal that feeds mainly on bark, aquatic vegetation, roots and shoots. They are particularly fond of trees such as aspen, birch, willow and maple.
• Reproduction: this occurs in early summer. Copulation can take place on land or in water. The gestation period lasts between 100 and 110 days, after which two to four young kits are born in each litter. They weigh between 250 and 600 grams. Newborns have fur and partially open eyes, but they are not precocial. Although lactation lasts for about three months, the young begin consuming solid food a few weeks after birth. Sexual maturity is reached between one and a half and two years of age. At that point, the young are forced to leave the colony by their parents to seek out their own territory. In the wild, they can live up to 24 years, but their life expectancy can extend to 50 years in captivity.
• Conservation: although there are no major threats to the species in its range, it is hunted with traps for its fur.

Now we know the characteristics of the North American beaver, we can see how they compare and contrast with those of the Eurasian beaver (Castor fiber) depicted in the photo below:

• Distribution: the Eurasian beaver was once widespread across Europe. Overhunting has drastically reduced its current population, leaving it isolated to some regions of the Rhône (France), Elbe (Germany), southern Norway, Neman River, Dnieper Basin (Belarus) and Voronezh Basin (Russia). Thanks to conservation and reintroduction measures, the Eurasian beaver has returned to much of its former range. There are currently several subpopulations extending from Spain and France through to Eastern Europe and Russia.
• Habitat: like the North American beaver, the Eurasian beaver has adapted to a semi-aquatic lifestyle, utilizing a variety of freshwater environments such as rivers, streams, ditches, lakes and swamps. It typically prefers freshwater habitats surrounded by forest or brush, although it can also be found in agricultural fields or even urban areas. It can build dams to retain water, create food reserves, provide safe shelter and facilitate the transport of woody material. It hides and rests in burrows.
• Behavior: they also create dams, modifying their environment to create safe havens and facilitate access to food. They are also nocturnal and live in family groups consisting of a pair of adults, young and sub-adults (betweem 1.5-2 years of age).
• Size and weight: the Eurasian beaver is the largest type of beaver species, weighing between 15 and 20 kilograms. It usually measures between 73 centimeters and 1.35 meters.
• Coat: similar to that of the North American beaver, the Eurasian beaver coat has two layers, a soft and dense dark-gray undercoat, and an outer coat with stiff, long and reddish-brown hairs.
• Diet: as with C. canadensis, the Eurasian beaver is herbivorous. It feeds mainly on aquatic and terrestrial herbaceous vegetation and broad-leaved woody vegetation.
• Reproduction: the mating season begins in late winter, with copulation generally taking place underwater. The gestation period lasts about 100 days, giving birth to between two and five young. These are born with their eyes open and covered in fur. In the first weeks of life, they remain within the burrow with their mother and the previous season's young. Sexual maturity usually occurs after two years of age, at which time they usually leave the colony and establish their own territory.
• Conservation: the decline in their populations is primarily due to overhunting for fur, meat and castoreum (a scent gland secretion). The loss of wetlands has also affected population numbers. Some rewilding programs have shown positive results, such as those seen in Scotland where it maintains a protected status.

One of the key differences between North American and Eurasian beavers is genetic. Eurasian beavers have 48 chromosomes, whereas the North American beaver only has 40 chromosomes. This prevents the two species from mating with each other.

You can discover more about the diversity of different animal species with our article sharing the different types of mammals.

If you want to read similar articles to Different Types of Beavers, we recommend you visit our Wild animals category.