Beaver
Large semiaquatic rodents that build dams and lodges.
Beavers (genus *Castor*) are large, semiaquatic rodents native to the Northern Hemisphere. Two species exist today: the North American beaver (*Castor canadensis*) and the Eurasian beaver (*Castor fiber*). They are the second-largest living rodents after capybaras, with stout bodies, large heads, long chisel-like incisors, brown or gray fur, hand-like front feet, webbed hind feet, and flat, scaly tails. The two species differ in skull shape, tail shape, and fur color; the Eurasian beaver is slightly longer, has a more elongated skull, triangular nasal cavities, lighter fur, and a narrower tail. Beavers inhabit freshwater environments such as rivers, streams, lakes, and ponds. They are herbivores, feeding on tree bark, aquatic plants, grasses, and sedges. Beavers are renowned for building dams and lodges from tree branches, vegetation, rocks, and mud, felling trees for construction material. Dams restrict water flow to create ponds, while lodges—typically built in these ponds—serve as shelters. This infrastructure forms wetlands that support many other species, making beavers a keystone species. Adults live in monogamous pairs with their offspring; young help repair dams and lodges after their first year, and older siblings may assist in raising new pups. Beavers defend territories using scent mounds of mud, debris, and castoreum, a substance excreted from their castor sacs. They recognize kin through anal gland secretions and are more tolerant of relatives as neighbors. Historically, beavers were hunted for fur, meat, and castoreum, which was used in medicine, perfume, and food flavoring. Overhunting nearly exterminated both species before protections began in the 19th and early 20th centuries; populations have since rebounded, and both are listed as least concern by the IUCN. In human culture, the beaver symbolizes industriousness and is the national animal of Canada.
- Scientific name
- Castor (genus)
- Extant species
- Castor canadensis and Castor fiber
- Head–body length
- 80–120 cm (31–47 in)
- Tail length
- 25–50 cm (10–20 in)
- Chromosome count
- Eurasian: 48; North American: 40
- Conservation status
- Least concern (IUCN)
Lore & Background
Beavers build dams and lodges using tree branches, vegetation, rocks, and mud, chewing down trees for building material. Dams restrict water flow, forming ponds, while lodges serve as shelters. Their infrastructure creates wetlands used by many other species, and because of their effect on other organisms in the ecosystem, beavers are considered a keystone species. Adult males and females live in monogamous pairs with their offspring; after their first year, the young help repair dams and lodges, and older siblings may help raise newly born offspring. Beavers hold territories and mark them using scent mounds made of mud, debris, and castoreum, a liquid substance excreted through the beaver's urethra-based castor sacs. They can also recognize their kin by anal gland secretions and are more likely to tolerate them as neighbors.
Reader's Guide
Historically, beavers have been hunted for their fur, meat, and castoreum. Castoreum has been used in medicine, perfume, and food flavoring; beaver pelts have been a major driver of the fur trade. Before protections began in the 19th and early 20th centuries, overhunting had nearly exterminated both species. Their populations have since rebounded, and they are listed as species of least concern by the IUCN Red List of mammals. In human culture, the beaver symbolizes industriousness, especially in connection with construction; it is the national animal of Canada. The two species differ in skull and tail shape and fur color, and the difference in chromosome numbers (Eurasian: 48; North American: 40) prevents them from interbreeding. Beavers are the only extant members of the family Castoridae, and they originated in North America in the late Eocene, colonizing Eurasia via the Bering Land Bridge in the early Oligocene.
Did You Know?
- Beavers build dams and lodges using tree branches, vegetation, rocks, and mud.
- Castoreum, excreted through the beaver's castor sacs, has been used in medicine, perfume, and food flavoring.
- The Eurasian beaver has 48 chromosomes, while the North American beaver has 40, preventing interbreeding.
Frequently Asked Questions
What is a beaver?
A beaver is a large, semiaquatic rodent belonging to the genus Castor, native to the Northern Hemisphere. They are best known for constructing dams and lodges in and around freshwater habitats.
How many species of beaver are there?
There are two living species: the North American beaver (Castor canadensis) and the Eurasian beaver (Castor fiber). They differ in chromosome count, with the Eurasian species carrying 48 chromosomes and the North American species carrying 40.
Why are beavers considered a keystone species?
By building dams and lodges, beavers create and maintain wetland habitats that support a wide variety of other plants, fish, and invertebrates. Their engineering work reshapes entire ecosystems far beyond their own needs.
What makes beavers unique among rodents?
Beavers are the only rodents that actively engineer their environment on a large scale, felling trees and constructing complex water-management structures. Their combination of size, semiaquatic lifestyle, and dam-building behavior sets them apart from virtually every other rodent group.
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