Beaver Links


Quotes from Water by Alice Outwater

     "Beavers do more to shape their landscape than any other mammal except for human beings, and their ancestors were building dams ten million years ago. These Miocene beavers were 7 feet long, felling trees ages before the mammoths roamed. Their underground spiral burrows can be found from western Europe to central Asia and North America; . . . Legends of these prehistoric giants were once widespread. The Indians of Nova Scotia claimed to know of an ancient beaver dam so vast that it flooded the Annapolis Valley; farther west, tales circulated of tribal ancestors using immense beaver teeth to hollow out their canoes. 

     " In tribes across North America, legend had it that the beaver helped the Great Spirit build the land, make the seas, and fill both well with animals and people: Long, long ago when the Great Waters surged in a blind and shoreless world, the gigantic beaver swam and dove and spoke with the Great Spirit. The two of them brought up all the mud they could carry, digging out the caves and canyons and shaping the mud into hills and dales, making mountains where cataracts plunged and sang. Some tribes believed that thunder was caused by the great beaver slapping his tail."

     "It is estimated that as many as two hundred million beavers once lived in the continental United States, their dams making meadows out of forests, their wetlands slowly capturing silt. The result of the beaver's engineering was a remarkably uniform buildup of organic material in the valleys, a checkerboard of meadows through the woodlands, and a great deal of edge, that fruitful zone where natural communities meet. Beavers are a keystone species, for where beavers build dams, the wetlands spread out behind them, providing home and food for dozens of species, from migrating ducks to moose, from fish to frogs to great blue herons."

     "The beaver is a clever engineer, but its brain is embarrassingly small . . . Beaver's don't have much gray matter, and they don't see well. Nevertheless, there is abundant evidence . . . that much of their building technique appears to be learned through their long childhood. Oddly, although the European beaver, Castor fiber, is nearly identical in appearance to the American beaver, it has no interest in dam construction; in most regions, European beavers confine their efforts to digging burrows in the stream bank. It seems likely that the fine points of dam construction were lost to Castor fiber during the centuries when only a few survived in parks."


Beaver are more than intriguing animals with flat tails and lustrous fur. American Indians called the beaver the "sacred center" of the land because they create rich habitats for other mammals, fish, turtles, frogs, birds and ducks. Since beaver prefer to dam streams in shallow valleys, much of the flooded area becomes wetlands. Such wetlands are cradles of life with biodiversity that can rival tropical rain forests. Almost half of endangered and threatened species in North America rely upon wetlands. 

Besides being a keystone species, beaver reliably and economically maintain wetlands that can sponge up floodwaters, prevent erosion, raise the water table and act as the "earth's kidneys" to purify water.

 A Bit About Beaver

Beavers' ability to change the landscape is second only to humans. But that is just one reason why we find the flat-tailed species fascinating. Adults may weigh over 40 pounds, and beaver mate for life during their third year. Both parents care for the kits (usually one to four) that are born in the spring. The young stay with their parents for two years, and yearlings act as babysitters for the new litter. While some beaver behavior is instinctive, they also learn by imitation and experience. Dr. Donald Griffin, the father of animal cognition, says "When we think of the kinds of animal behavior that suggest conscious thinking, the beaver comes naturally to mind."

Wildlife rehabilitators find beaver to be gentle, reasoning beings with a sense of humor. An Indian word for "beaver-like" also means "affable." Once weaned, their favorite foods include water lily tubers, clover and the leaves and the green bark (cambium) from poplar and other fast-growing trees. Tree cutting is part of nature's cycle and beaver pruning stimulates willows to regrow bushier than ever next spring. After eating, beaver often use the peeled sticks to build a teepee-like lodge (house) on the shore and/or a dam.

By damming streams, beaver raise the water level to surround their lodge with a protective moat, and also create the deep water needed for winter food storage in northern climes. While other wildlife endure wintertime cold and hunger, beaver stay warm in their lodges with an underwater food cache nearby. A beaver colony, often consisting of six or more including parents, yearlings and kits, coexists peacefully in a lodge with underwater access to the iced-up pond for four months or more.

Because they breed once a year, require large streamside habitats, and two-year-olds leave home each spring to find their own territories, beaver rarely overpopulate. Small kits have many predators including hawks, owls, bobcat, coyote and dogs. Bear, wolves, dogs and coyote can also take adults.

Like most wildlife, beaver self-regulate by starting to decrease their rate of reproduction when occupancy reaches a certain level. In vast areas without trapping, beaver populations may peak, and then slowly drift down to a sustainable level. Beaver in North America were almost extirpated by overtrapping in the early 1900s, and estimates of the current population are as low as 2.5% of those present prior to European settlement. Nonetheless, as beaver reclaim some former territory, conflicts with humans do arise.


Beaver require deep water for protection from their enemies, and they alter the landscape a great deal with dam building and flooding. Dams can be hundreds of feet in length, and vary in height from only a few feet to 7 or 8 feet, and even higher at times.

Permanent lodges are often constructed by piling layer after layer of sticks into a large conical form above the waterline.  Two or more underwater tunnels are then chewed up into the pile, and an inner chamber hollowed out to serve as a living quarters Finally the outside of the lodge is plastered with mud and rocks, except for the peak, which is left porous enough to allow an air exchange to the inner chamber. There are two levels to the chamber. One level is near the waterline near the "plunge holes", where the beaver shed water before climbing to the higher resting or nesting areas.

In areas prone to flooding, or where strong currents may be present, beaver usually construct bank dens by digging tunnels from underwater up into banks. Bank dens often have two or more submerged entrances. Many times the beaver will construct a pile of sticks over the tops of the underground living chambers. These piles of sticks are sometimes called "caps".

Shallow pockets are sometimes dug into banks near the waterline and these are known as "feed pockets". In northern areas, beaver construct "feed piles" by submerging large amounts of small trees and limbs to serve as a food source after ice prevents th beaver from activity above the ice. These feed piles are usually constructed close to the den as a convenience to the kit beaver, who do not normally travel far from the den itself.

At times, solitary beaver will be found living alone. These beaver are known as "bachelors", whether they are male or fernale.

Adult beaver mark out their territories in early spring by dragging up mud and debris from the bottom and depositing the debris in mounds along the shores, where they also deposit oil from their castor glands. These "castor mounds" often leave a reddish stain on the bank, and the odors are powerful enough for a human to easily detect.

Beaver are very territorial, and territories seldom overlap. Generations of beaver may continuously inhabit a choice area, even building canals to help float food from inland cutting sites. If and when food supplies are exhausted, they do relocate to better area. Once beaver have determined to claim a territory, they are very difficult to dissuade. If the activities of the beaver flood roads or damage property, the beaver usually have to be removed to prevent reoccurring damages.

Although beaver normally submerge for 3 or 4 minutes at a time, they are quite capable of holding their breath for 12 to 15 minutes. They exhale a little in spurts as they swim or work under water, and a large beaver is quite capable of traveling nearly 1/2 mile under the surface before it must surface for more air.

Migrations of beaver usually occur with the breakiing up of ice in late winter or early spring as the 22 or 23 months old beaver are expelled just prior to birthing time for the new litter. These beaver may chose to go up or downstream. Although these beaver are capable of reproducing, they usually do not until the next season, after a mate and a new territory have been established. Most new colonies are established within a few miles of the home colony.

Beaver are primarily vegetarians although an occasional beaver may eat a dead fish [I'm not sure that this mention of dead-fish eating is based on actual observation. bobk]. Preferred foods include the bark of aspen, willow, cottonwood, and dogwood, and many other varieties of trees and shrubs. In early spring, beaver will often eat bark a twigs of evergreens. In season, beaver will also eat water lillies, leaves, grassses, roots, and a variety of crops including corn, wheat, oats, carrots, potatoes, apples, clovers, and alfalfa.


By Margaret Orgill

ESTANCIA VICUNA, Chile, Feb 29 (Reuter) -

In North America they are admired for their industry, buck teeth and all around cuteness. Here at the southern tip of South America, they are: THE PLAGUE THAT CAN'T BE STOPPED.

Jose Luis Garcinuno drives his pickup truck down a dirt track through the cool, pristine beech forests on the island of Tierra del Fuego. Suddenly a wasteland of dead trees, stagnant pools and fallen logs opens up on every side.

``It's the beavers again,'' said Garcinuno, a forestry engineer, pointing to the mass of neatly chiseled trunks littering a riverbank.

The descendants of 26 pairs brought from Canada in the 1940s by fur breeders are running riot in the backwoods of this island at the southern tip of Latin America and officials are unsure what, if anything, they can do about it.

``Beavers are a plague. They are creating an important imbalance in the environment,'' said Ander Uriarte, forestry engineer at Chile's National Environment Commission.

``They are causing significant damage to forests throughout Tierra del Fuego and neighbouring islands.''

Even greater damage could happen if the animals manage to spread to the mainland across the Straits of Magellan -- a dire prospect for Chilean environmentalists and forestry companies.

On Tierra del Fuego's remote southern slopes, the beavers, a symbol of the vast boreal forests of North America, have gnawed away at the unique Andean beech woodlands.

Lack of predators allowed the animals to spread across the island and more recently they have crossed by swimming or clinging to floating logs -- no one knows exactly how -- to nearby Navarino and other islands, and possibly the mainland.

One area of sparsely-populated Tierra del Fuego, which is shared between Chile and Argentina, has so many colonies of the animal that locals have dubbed it Valle de los Castores -- Valley of the Beavers. One problem is getting locals to view these furry, industrious animals as the plague that officials feel they are.

``Just because they are pretty animals, unlike rats, people don't think beavers are a pest,'' said Gonzalo Sainz, head of the regional tourist board in Punta Arenas.

Tierra del Fuego's windswept plains and thickly forested mountains are home to a rich variety of native wildlife including flamingos, foxes and guanaco, a cousin of the llama.

Unfortunately for local wildlife officials, none of these animals hunt beavers, unlike in North America where bears help keep their numbers down.

``As beavers live in remote areas, there is nothing to disturb them and they live completely freely,'' said Uriarte.

Prized for their glossy caramel-coloured pelts, the first animals were brought by fur breeders to a farm in the Argentine sector of the island in 1946. The business folded within a few years and the beavers escaped or were abandoned.

With no natural predators, an agreeable cool climate similar to their native lands and miles (kms) of untouched forest, the beavers had found paradise. Their numbers exploded, said Sainz.

There are reports the animals have crossed the Straits of Magellan to the mainland, with potentially devastating consequences for the region's environment, say experts.

``The spread of beaver northward along the Andes in Chile into areas with much higher stream densities could signify a major ecological disaster in southern South America,'' said a report commissioned by U.S. forestry company Trillium and carried out by a team of scientists led by University of Chile biologist Mary Kalin Arroyo.

Along riverbanks in Trillium's land, beavers had damaged between 25 and 75 percent of the trees, said the report.

But the report noted lower densities on the Argentine side, where beavers are more often hunted than in Chile, and that densities on both sides of the border were lower than in the animals' natural habitat in Canada.

The long-toothed mammals fell trees to dam streams, creating still-water pools where they build their nests. As soon as the water level rises the dams cause flooding which drowns trees growing close to the riverbanks. They also kill young saplings by nibbling at their bark and shoots.

``We definitely have a problem with the beavers and it's under study,'' said Gordon Thompson, the head of operations at Trillium. The Bellingham, Washington-based company, which owns a vast area of virgin forest on the island, is starting a controversial project this year to log and manage the woodlands.

Scientists have said their only hope is to contain the beavers on the land they have already invaded. They saw no chance of eradicating them.

``There are so many beavers that trapping is not a realistic option as more would just come across from the other side of the island,'' said Thompson.

``Any local attempt to eradicate the beaver will be largely futile,'' despaired the Trillium report, adding the company ``should explore humane ways to control the beaver population.''


Then And Now - Giant Beaver

The giant beaver (Castoroides ohioensis) was the largest rodent in North America during the ice age (Quaternary - the last 2 million years). How did it look? How large was it? How is it related to living beavers (Castor sp.)? These are just a few of the questions people ask when they first hear about the giant beaver.

Unlike the woolly mammoth (Mammuthus primigenius), cave bear (Ursus spelaeus) and steppe bison (Bison priscus) whose images are so vividly recorded on the walls of European caves by Stone Age (Paleolithic) hunters, there is no record of the giant beaver's actual appearance. However, the great similarity between giant beaver and modern beaver skeletons leaves no doubt that the two animals were much alike in appearance and were adapted to similar surroundings.

But there was one remarkable difference size! A skeleton displayed in Chicago's Field Museum is nearly 2.5 m long the size of a black bear (Ursus americanus). An animal of this size may have weighed as much as 200 kg compared to a 1 m-long modern beaver weighing about 30 kg. Modern beavers are, to put it simply, "distant cousins" of Castoroides.

Other differences were in the teeth and tail of the giant beaver. Unlike modern beavers with their short smooth-surfaced cutting teeth (incisors), giant beavers had cutting teeth up to 15 cm long with prominently-ridged outer surfaces. Perhaps these strong enamel ridges would have acted as girders to support such long teeth. Although experts on ancient life (paleontologists) do not agree on the function of the cutting teeth, it seems that they could have acted as both wood cutters and gougers. Giant beaver cheek teeth also differ from those of modern beavers in their larger size and simpler enamel configuration. Molar teeth of Castoroides, like its relatives Dipoides and Procastoroides, typically have grinding surfaces with an s-shaped enamel pattern.

By studying the length and width of giant beaver tail vertebrae in relation to those of modern beaver and its actual tail dimensions, I estimate that Castoroides had a scaly tail that was about 65 cm long, 12 cm across the base and 14 cm across the widest part. Definitely a beaver-like tail, but relatively narrower. Although well adapted for swimming, the hind legs of giant beavers are relatively short. Considering the great weight of the animals, their ability to disperse overland as some living beavers do, would have been reduced.

The first recorded remains of this animal were found in a peat swamp near Nashport, Ohio, and were described, but not named, by S.R. Hildreth in 1837. The geologist J.W. Foster called the specimen Castoroides ohioensis in a publication a year later.

What about their ancestry? A primitive beaver called Dipoides that occupied Eurasia and North America during the late Tertiary (some 5 million years ago) evidently gave rise to Procastoroides, a large beaver about two-thirds the size of the giant beaver. It is worth noting that slight enamel ridges were first seen on the cutting teeth of the Idaho beaver (Procastoroides idahoensis), although the closely related Sweet's beaver (Procastoroides sweeti) lacked them. So probably the Idaho beaver, or a very closely related form, gave rise to the giant beaver about 3 million years ago. A study of the development of the cheek-tooth pattern in giant beavers also supports the Dipoides - Procastoroides - Castoroides lineage.

Another "giant beaver" (Trogontherium - not much bigger than a modern beaver) lived in Europe and Asia during the early part of the ice age. Despite some basic similarities in shape, Trogontherium and Castoroides are at extreme ends of two different lineages. However, perhaps both had developed similar ways of living in relation to modern beavers, with which they coexisted.

Castoroides ranged from Florida to the Yukon, and from New York State to Nebraska, but it has not been found outside of North America. Giant beavers seem to have flourished in the region south of the Great Lakes toward the close of the last glaciation. In fact, three nearly complete specimens are known from Fairmont and Winchester, Indiana, and from Minneapolis, Minnesota.

The most northerly records are from the Old Crow region of the Yukon Territory (1), which lies 150 km north of the Arctic Circle. Here, many fossils (consisting largely of jaws, teeth, leg bones and vertebrae) have been found in deposits varying in age from the last Sangamonian) interglacial (about 130,000 years ago) to the early part of the last (Wisconsinan) glaciation (about 60,000 years ago)(2). Fossils show that both giant beavers and modern North American beavers (Castor canadensis) coexisted near Old Crow during the last part of the ice age. The only giant beaver fossil found elsewhere in Canada is a cutting tooth from last interglacial deposits in the Don Valley, Toronto.

How did giant beavers get so far north? And when? Perhaps they spread rather rapidly northward into the Yukon through chains of lakes which tend to form along the southern margin of the Canadian Shield (for example, during the present interglacial - the relatively warm period covering the last 10,000 years some are: Lake Superior, Lake Manitoba, Lake Athabasca, Great Slave Lake and Great Bear Lake). A likely time for this northward shift would have been near the beginning of a warm period such as the last interglacial, when ice sheets of the second last (Illinoian) glaciation were melting back.

Where did giant beavers live? A possible giant beaver lodge was discovered near New Knoxville, Ohio about 1912. Part of a Castoroides skull and the lodge were located in a peaty layer surrounded by loam. The lodge was said to have been roughly 1.2 m high and 2.4 m in diameter, and formed from saplings about 7.5 cm in diameter.

Giant beavers seem to have preferred lakes and ponds bordered by swamps as their habitat, because their remains have been found in ancient swamp deposits so often. Perhaps a rather sudden reduction of these surroundings due to changing climate linked with the giant beaver's apparent inability to build dams like those of Castor canadensis and its inability to disperse readily overland to new drainage systems when drought occurred may have resulted in its extinction and the survival of the smaller, more adaptable modern beaver. Likewise, the Eurasian "giant" beaver, Trogontherium, gave way to the living Eurasian beaver (Castor fiber), but earlier.

Giant beavers evidently died out near the close of the last glaciation about 10,000 years ago. Because they coexisted with early humans in North America, it seems unusual that there is no evidence that people hunted them. Surely a Castoroides pelt would have made an excellent coat or sleeping robe!

C.R. Harington
March, 1996
Giant Beaver.
Reproduced courtesy of the Canadian Museum of Nature, Ottawa


The following is an excerpt from Everett S. Allen's: A Wind to Shake the World: The Story of the 1938 Hurricane.

At Stony Point, NY, 60 colonies numbering more than 500 beavers manned their dams in the park's 42,000 acres when the storm broke. There were 60 dams in the beavers' defense line, the principal restraining force against rain-swollen rivers, streams, and ponds.

The size of the problem confronting the animals was impressive. Long Mountain beaver pond, for example, was created by a dam in what was normally a three-foot-wide stream; the pond ordinarily covered about five acres in the center of the park. On Wednesday night, with a roiling stream widened to almost 20 feet and the pond doubled in size, the beaver dam, made of mud, sticks, stones, and sod, withstood the pressure and fed 18 inches of fast-moving water over its top.

Another dam of critical importance was wedged between boulders 30 feet apart; as with all the others, it was completely submerged at the storm's peak, yet never showed a sign of yielding to the strains of water upon it. John J. Tamsen, superintendent of Bear Mountain Park, and William H. Carr, director of the Trailside Museum, maintained by the American Museum of Natural History, credited the beavers - who cut down trees all through the night of the hurricane to reinforce their wood-and-mud bulwarks - with having saved three arterial highways from serious flooding, preventing the certain destruction of at least one bridge, and retarding the erosion of hundreds of acres of soil.

Carr said had it not been for the beaver dams "backing up perfectly terrific bodies of water, in some cases, more than 200 yards across," Long Mountain Road, U.S. Highway 6, and the Johnstown Road would have been transformed into rivers for distances of up to a quarter of a mile and the same would have held true of U.S. Highway 9W, the main road along the west shore of the Hudson, and Route 17 linking Tuxedo park and Harriman, to the north.

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