At the Zoo: Busy Beavers
by Amy Himes
O my friend Ahmeek, the beaver,
Cool and pleasant is the water;
Let me dive into the water,
Let me rest there in your lodges;
Change me, too, into a beaver!—Henry Wadsworth Longfellow, "Song of Hiawatha" (1855)
Metro Orange Line. 5:10 p.m. The
man sitting next to me on the Washington Metro subway car
peers over my shoulder and asks what I'm reading. I flip the
book over to show him the cover.
"Beavers…ah, beavers," he says, throwing his head back and gazing past me with a faraway look in his eye. "I used to shoot 'em and skin 'em. We'd blast 'em out with dynamite."
"You what?"
"Well, you know, we'd spend our summers hunting beavers. You could get $20, well, no, maybe up to $40 for their hides. That was a lot of money in those days."
"Where did you hunt beaver?" I ask.
"Western Colorado. There were so many beavers then," he says. "Are there any beavers around Washington, D.C.?"
"Sure,"
I tell him. "Remember the news stories from a few years
ago about the beaver downing the cherry trees in the Tidal
Basin?" Park Service officials were certain that a beaver
was the culprit, as the trees had been gnawed through, leaving
a pointed stump remaining—the rodent's trademark. They
quickly removed the felled trees in an effort to thwart the
beaver's natural urge to build a dam. A family of three beavers
was eventually trapped and relocated.
At one time beaver populations were found throughout the Northern Hemisphere. The domain of the European beaver (Castor fiber) extended from Portugal and the British Isles all the way into northern Scandinavia, Siberia, and Mongolia. After being hunted to extinction in the British Isles—and most of Europe and Asia—European beavers now remain in only a few small pockets of their former range.
The North American beaver (Castor canadensis) inhabits much of the continent, with the exception of the northernmost Yukon, arid areas of the southwestern United States, and some coastal areas in the southeast. Otherwise, the industrious rodents—once on the verge of extinction in North America—inhabit almost every forested area from coast to coast and from the Gulf of Mexico north to the Arctic Circle.
Healthy forests are crucial to beaver survival. Their sickle-shaped teeth are adapted to serve as tools for chipping and gnawing through wood. Like many rodents, these animals must wear down teeth that grow continuously throughout their lives. The cutting action of incisors wears down the surface of the teeth at the same time it sharpens them. Without the constant abrasion, a beaver's teeth may grow too long, making the animal unable to eat.
Beavers prefer to eat softwood trees that are only a few inches in diameter, and they select some of the most abundant and fastest-growing trees in North America, including aspen, poplar, and willow. Their diet may also include grasses, fruits, fungi, lichens, and water plants. Beavers choose smaller trees because they are faster to fell and are easier to carry. Since time out of the water leaves beavers vulnerable to predators—such as hawks, wolves, foxes, bears, and coyotes—felling smaller trees allows the beaver to finish business and head for cover faster.
That cover is the water of streams, rivers, and lakes where these busy engineers of the forest build their lodges and dams. With webbed hind feet, short front legs, and flaps in the mouth, throat, and eyes that evolved especially for life in the water, beavers are excellent divers that may stay beneath the surface for four to five minutes at a time. But these aquatic rodents haven't managed to hide from their most prolific predators: people.
The Fur Trade
"I've felt a beaver fur," I say.
"Huh?" my Metro seatmate replies.
"At a museum on Mackinac Island, in Michigan, I felt beaver's fur. All sorts of furs were laid out for people to touch: otter, red fox, raccoon, muskrat, squirrel, and beaver."
The beaver's fur was plush, the richest and softest fur on display. Beaver fur consists of two coats: an inner undercoat and an outer coat. The outer "guard" hairs, which give the beaver its grayish or rusty brown color, are coarse, thick, and shiny due to oil produced by oil glands. A beaver grooms its fur by using its front feet to spread the oil discharged from its cloaca, a cavity that serves as an exit for the intestinal, genital, and urinary tracts in beavers and certain other primitive mammals. This special oil is critical in waterproofing the fur. The fur's slick, smooth texture helps the beaver glide through water easily. Beavers molt their outer coats during the spring and summer months.
The inner layer of fur consists of fine, soft hairs that pile over the entire body except the feet and tail. Not only is the undercoat dense, the hairs' rough scales cause it to mat together, trapping and insulating air that warms the animal in freezing weather. Beavers' fur, adapted to their watery environment, helps the animals keep warm and dry during extremely cold winters. Unfortunately for beavers, these same qualities have made their pelts highly desirable to humans.
Early written laws in Britain declared the beaver as property of the king. Beaver fur—a symbol of royal power—was hemmed to the borders of the royal family's robes and other garments. Its fur could cost up to five times more than the fur of other animals. In the 1600s, the colonization of North America led to explosive trade in pelts. Native Americans hunted the beavers—hacking their lodges, shooting them with bows and arrows, catching them with their hands, or setting traps—in order to exchange the fur for settlers' goods. By 1670, the Hudson's Bay Company, a monopoly licensed by Britain's King Charles II, harvested all the fur from watersheds leading to the bay. The monopoly fostered competition over trapping territory between the English, Native Americans, and French-and helped spark the French and Indian War.
The beaver fur trade also encouraged settlement and exploration of the West. Cities such as Albany, St. Louis, and Mackinac City were founded by the trade. The New York City seal depicts a beaver, as do many Canadian and English family crests. According to many historians, the beaver—a symbol of industry and perseverance—contributed more to the development of North America than any other animal.
"Mackinac beavers made the first millionaire," says Jeff Dykehouse, the Mackinac Island interpretation supervisor and chief naturalist of Michigan's historic parks. Controlling this fort built by British soldiers during the American revolution, John Jacob Astor chartered the American Fur Company in 1808, a business that helped him die the richest man in America. According to Dykehouse, five to ten beaver furs were traded for every one fur of all other animals in the Mackinac and Great Lakes trade combined. "Hundreds of thousands of beaver furs went through the straits of Mackinac, because it was located halfway in-between [many major Canadian trading posts] and Albany," he says.
Hunters usually trapped beavers but would also employ other methods, such as cutting holes in ice. Beavers use such holes for access to food and fresh air and are easily caught as they emerge. Another method was attacking lodges while blocking the openings for escape, trapping beavers inside. Hunters even destroyed dams to lure the animals, as beavers instinctively react to the sound of rushing water in order to safeguard their structures.
By the early 1800s, beaver fur trade reached its height amid an expanding consumer market. Hundreds of thousands of pelts were shipped each year from Canada to Europe. Men's felt hats were the fashion rage in Europe and the United States, placing heavy demand upon beaver fur. In the 1830s, when buffalo hunting's popularity grew and trade with China made silk the newest fashion, the beaver went out of style, although some hunting and trapping has continued to this day.
Nose to Tail
Unlike my Metro acquaintance who sought beavers only for their pelts, many people hunted beavers for another reason, one originally considered far more valuable than fur.
Castoreum, an oily substance produced by the castor glands, is a strong-smelling compound that beavers use to mark territories and identify other beavers. Two castor glands—each measuring up to four inches long in adults and found near the base of the tail—emit the castoreum liquid through the cloaca. Beavers create mounds of mud about one to two feet in width and height to scent-mark their territory along the edges of waterways. Adults visit these sites almost daily to deposit castoreum. A powerful signal to other beavers, the scent may be detected from a distance, warning potential intruders to stay away.
In ancient times, healers in Europe and North America used castoreum to treat fever, gout, epilepsy, toothache, tuberculosis, arthritis, and other ailments. The Greek Hippocrates—considered the father of medicine—recommended castoreum for its healing powers. In the Middle Ages, Europeans used it as a cure for snake and spider bites, deafness, poor eyesight, tumors, and even bad memory. Incidentally, castoreum has been found to contain small amounts of salicylic acid, which is found in the bark of one of the beaver's favorite trees, the willow. Salicylic acid is the active ingredient in aspirin.
By the early 1800s, the height of the beaver fur trade saw thousands of pounds of castoreum shipped to Europe from Canada. Because the dense, oily compound absorbs scents and releases them slowly, perfumers added fragrances to castoreum. Castoreum has been used as a base to which fragrances are added even in modern times.
Castoreum was once thought to enhance sexual energies-an erroneous connection between the oil and beavers' sexual activity. Indeed, beaver sexual function fascinated early cultures because, unlike most mammals, beavers have no external difference in sexual organs that may distinguish one sex from the other. In many males, the external sexual organs look almost exactly like the female's. The penis and testicles are hidden inside the urogenital passage that opens into the cloaca. Some males even have a non-functioning uterus. Because of the absence of external sex organs, ancient Egyptians as well as European writers until the 1600s believed beavers would castrate themselves if threatened with capture. Some Christians even associated certain saints with the supposedly chaste beaver.
People hunted beavers for other reasons besides furs and glands. Native Americans hunted the animals for meat long before Europeans arrived in North America. During the Middle Ages in Europe, beaver tail was considered a delicacy fit for royal dining. In the 18th century, when many people considered beavers to be fish, Catholics were allowed to eat these mammals during periods in which other meats were banned.
If you walk into a Canadian bakery today, you'll likely find "beaver-tail doughnuts"—a (meatless) fried pastry with a waffled pattern in the shape of the beaver's distinctive paddle-like tail. Often mistaken for its smaller rodent cousin, the muskrat, the beaver is best recognized by this broad, flat tail with hard ridges that look like scales. The tail—its center an extension of the spine—may grow to about 18 inches long and six inches wide. Fat inside the tail serves as a source of stored energy and temperature control for the body. Beavers use their tails as a rudder when swimming, as a balancing device when gnawing trees or dragging limbs, and as an alarm when slapping the water.
Good News
"I haven't seen any beavers," the man on the Metro says, "but I hear they're making a comeback, aren't they?"
Indeed they are. In North America alone, beavers, which originally numbered anywhere from 60 to 400 million before nearly going extinct, are now thought to number six to 12 million. The animals remain threatened by water pollution, reclamation of wetlands, and hydroelectric plants. Beavers are being reintroduced into pockets of the United States, Scandinavia, and Russia from which they had vanished. However, such introductions may cause problems. If the North American beaver is introduced into Europe and Asia, evidence suggests that it may out-compete the native species. Also, farmers and ranchers complain of flooding and damage to crops, fields, and roads in places where beavers have returned.
Nonetheless, people are gradually learning to coexist with beavers—and for good reason. Beavers play a major role in their ecosystems by creating ponds where many species of plants and animals can thrive. Reservoirs control runoff and erosion. Beavers help maintain a healthy natural environment—for animals like us.
As the man slowly stands to exit the Metro, I ask him, "How long did you hunt beavers?"
"We did that for several summers," he says, then hesitates. "And then we got better jobs."
—Amy Himes is a former ZooGoer intern.
MORE! Beaver Basics
Because
beavers are generally nocturnal, the best time to see the
Zoo's five beavers—the father, Cleaver, mother Granby, and
their three offspring, Chipper, Buzz, and Willow—is during
daily feedings usually at 1 p.m. A recent expansion to their
outdoor exhibit allows them to forage for branches and logs
on dry land during the afternoon.
ZooGoer 31(2) 2002. Copyright 2002 Friends of the National Zoo. All rights reserved.
