Fun Beaver Facts

North American beaver (Castor canadensis)

North America’s largest rodent. World’s second largest rodent, second to South America’s capybara.

Beaver Habitat Range: riparian zones inclusive of the stream bed in most of North America except the furthest northern reaches of Canada and Florida’s peninsula.

Beaver Statistics

Total Length of 47” (120 cm), tail is 9‐13” (23‐32 cm)

Weight: 40‐60 lbs. but can grow to be over 70 lbs.

Genders are very difficult to determine; male and female beavers are the same size

Life expectancy: 10‐20 years in the wild

Uniquely Beaver

Rodents such as beavers have teeth that grow continuously. Their four incisors (2 upper and 2 lower) are composed of hard orange enamel outside and softer dentin inside. The chisel‐like ends of the incisors are maintained by their self‐sharpening wear pattern. The enamel of beavers’ incisors contains iron, giving them their orange color, providing greater hardness and resistance to acid.

Beavers have an extra transparent “eyelid,” called a nictitating membrane, that protects their eyes while allowing them to see below the water’s surface.

Beavers have a second set of fur‐lined lips that close behind their teeth and permit them to chew and drag wood without drowning.

Beavers usually stay underwater for 5‐6 minutes but can stay under for up to 15 minutes. They can swim up to 4.3 miles/hr (7km/hr). Beavers have powerful webbed hind feet that propel them through the water.

Beavers have an excellent sense of smell.

A beaver’s diet is made up of tree bark, aquatic plants such as water lilies and cattails, and also grasses and forbs. Their favorite tree barks are from aspens, poplars, cottonwoods, and willows. However, they will also eat birch, maple, black cherry, red oak, ash, hornbeam, and pine. Beavers practice caecotrophy, eating their own pudding‐like excretions to extract as much nutrition as possible. Beavers manage to digest about 1/3 of the cellulose they consume.

Beaver fur is soft and pliable and is made of two types of hair: coarse guard hairs about 2” long over luxurious underfur or wool. Their coats are thick, buoyant, and virtually waterproof.

The beaver’s flat scaly tail is a nifty multi‐tool, exquisitely adapted to semi‐aquatic life. It serves as a kickstand, a rudder, and an alarm system. The tail helps regulate body temperature and stores fat for leaner winter times.

The main predators of beavers are humans. Other important predators include black bears, coyotes and wolves.

Beavers are crepuscular (dawn and dusk activity) and nocturnal and can rebuild a dam overnight. Seldom a night passes when a beaver doesn’t inspect its dam and makes necessary repairs. Beavers do not hibernate.

Beavers live in families that range in size from 2‐10. The average family size is 6, including a breeding pair (usually monogamous), 2 kits and 2 yearlings born the previous spring. Yearlings mentor the newest generation for a while and then move on to establish their own families.

Beaver Populations

The estimated beaver population in North America before European settlement is 60–400 million. After nearly disappearing at the end of the 19th century, beaver populations recovered and are currently estimated to be 6‐12 million and they are thought to occupy much of their former range.

Beavers and Building

“Busy as a beaver”

Beavers build dams (walls of wood, mud, grass and rock) that hold back water forming upstream ponds and wetlands. The foundation includes a low ridge of mud, stones and sticks laid perpendicular to the stream’s flow. The addition of branches or other materials that are anchored and intertwined creates even more structure. Finally, the beavers caulk the gaps with mud, grass and leaves. The structures vary in size and shape.

Beaver dams slow down the water flow, capturing sediment and raising the height of the stream’s surface. Dams force water to spill out into the surrounding floodplain, furnishing meadows with nourishing sediments and transforming the stream into a maze of wetlands and side channels. In addition to dams, beavers often build lodges (mounds of logs and sticks) set into the stream bank or completely surrounded by water with an underwater entry. Inside, the inhabitants are safe from predators and protected from the elements and young (kits) can be raised. Typically, next to the lodge is an underwater food cache of twigs and branches, which is relied on heavily during the winter months.

Beavers are “messy” builders and, thus, willow sticks end up flowing downstream and sprout when they lodge in stream banks. In this way, beavers are responsible for sculpting stream banks with resultant bends and curves.

Beaver are considered ecosystem engineers because they can significantly change the hydrology of the landscape (e.g., increasing water table, increasing water storage capacity) as well as the number of species and habitats in the surrounding areas. As they fell trees, they also change both the plant community and the habitats available for other organisms. Among those species that benefit from beaver activity and the resultant increase in wetland area are moose, otters, trumpeter swans (that nest atop beaver lodges), and Coho salmon.

Note: In the Intermountain West, wetlands and riparian areas make up less than 2% of the total land area but support 80% of the biodiversity.

Streams, Beavers and Humans

Historically, streams seemed more like spaghetti with strands writhing, intertwining, and occasionally splitting off entirely and then rejoining further downstream (anabranching). However, humans straightened and channelized the waterways into the ribbons and strings we think of when we picture streams for easier navigation. Human settlers trapped the beavers, removed the dams, and reclaimed the nutrient‐rich soil for farming and animal grazing.

The 1500s were the beginning of the fur trade that sent hundreds of thousands of beaver pelts from North America to Europe and, ultimately, decimated their numbers. Many Indian tribes hunted beavers (as well as fur animals such as martens, fishers, minks and otters) and then traded them with European settlers such as the French and the British. By the mid‐1600s, many European settlers were also trapping beavers; in 1678, the French shipped almost 80,000 pelts from Quebec to Europe. Beaver pelts were traded and made into clothing and fashionable felt hats. The year of 1875 was the biggest beaver pelt harvesting year for Hudson Bay’s Company, sending over 270,000 furs abroad. At the peak of the fur trade, over x beaver pelts were probably harvested in a year. As trappers de‐beavered North America, dams deteriorated and ponds were drained leaving behind the finest soil a farmer could till.

A change in fashion changed the beavers’ fate. In the early nineteenth century, cheap silk became available to European hat makers just as the beaver pelts became prohibitively rare and expensive. In the late nineteenth century, North America began to snap out of the age of extermination and John Muir and Enos Mills extolled the virtues of nature. The first national park, Yellowstone, was established in 1872. Teddy Roosevelt continued to raise America’s conservation consciousness and created the first Federal Bird Reserve (precursor to today’s national wildlife refuges), founded the US Forest Service (1905), and protected approximately 230 million acres of public land.

In the early 1900s, work to reestablish the beaver across the continent was underway. Beavers were relocated and even dropped in by airplanes. By the mid‐1900s, beavers were back and well‐established in North America. Rural streams were allowed to “revert” to natural riparian areas with the help of the beaver.

By the 1980s, beavers were approaching their cultural carrying capacity in some high‐density areas. The cultural carrying capacity is the population (number of individuals) of a wild animal that humans can tolerate.

Unfortunately, in more urban areas, beavers began to dam up culverts causing roads to be flooded. To a beaver, an elevated road with a culvert is just a dam with a hole in it. Trapping was largely ineffective as one beaver would move into this prime spot when another was removed. These human‐beaver conflicts continue in some areas but we are finding some creative solutions. For example, specialists install flow devices (pipe and fence systems) that deceive beavers and prevent them from damming culverts. These efforts have been largely successful.

References

Baker, B. W., and E. P. Hill. 2003. Beaver (Castor canadensis). Pages 288‐310 in G. A. Feldhamer, B. C. Thompson, and J. A. Chapman, editors. Wild Mammals of North America: Biology, Management, and Conservation. Second Edition. The Johns Hopkins University Press, Baltimore, Maryland, USA.

Collen, P., & Gibson, R. J. (2000). The general ecology of beavers (Castor spp.), as related to their influence on stream ecosystems and riparian habitats, and the subsequent effects on fish–a review. Reviews in fish biology and fisheries, 10(4), 439‐461.

Goldfarb, B. (2018). Eager: The Surprising, Secret Life of Beavers and Why They Matter. Chelsea Green Publishing.

Muller‐Schwarze, D. (2011). The beaver: its life and impact. Cornell University Press.

Rosell, F., Bozser, O., Collen, P., & Parker, H. (2005). Ecological impact of beavers Castor fiber and Castor canadensis and their ability to modify ecosystems. Mammal Review, 35(3‐4), 248‐276.

Sokolow, J. A. (2016). The Great Encounter: Native Peoples and European Settlers in the Americas, 1492‐1800: Native Peoples and European Settlers in the Americas, 1492‐1800. Routledge.

[Compiled by Kim Kimpton and Karina Nabors, last updated November 2018]