The Original Lumberjack Is Still on the Job
HUMANS have invented many tools to cut wood, including axes, wedges, splitters, and saws. There are also tractors with knife-edged clamps that can cut through massive tree trunks. But the oldest woodcutting tools are not man-made. They are a good set of sharp teeth—those of the beaver, the original lumberjack.
An adult beaver can reach about four feet [1.3 m] in length and weigh upwards of 60 pounds [27 kg]. Because its upper and lower incisors grow continuously, the beaver must frequently abrade them. A layer of hard enamel lines the front surfaces of its incisors, giving them a sharp beveled edge. Curved inward and powered by very strong jaw muscles, these natural chisels cut the hardest wood with ease.
Warm Coat, Versatile Tail
People living in a cold climate appreciate the value of a warm, waterproof overcoat. Well, the beaver never has to shop for such outerwear, for it is endowed with a thick mantle of fur. Ranging in color from tan to dark brown, beaver fur has two layers. Ground hair, the dense undercoat, consists of very fine filaments lined with tiny barbs that lock together to protect the beaver against water and cold. Longer, thicker strands of guard hair shield the ground hair and aid the beaver in shedding water. Add a lustrous sheen and a plush feel, and no wonder many people prize garments made of beaver skin! Why, beaver pelts once even served as a form of money in Canada!
All beavers have two pairs of unusual glands at the base of the tail. One set furnishes a special oil, and the other produces castoreum, an aromatic secretion with a strong but inoffensive odor. The beaver puts these liquids to a number of uses, including waterproofing its fur and attracting other beavers. Castoreum is also of use to humans, for perfumers use it in some of their fragrances.
The beaver’s tail is unique. Shaped like a paddle, it is about a foot [0.3 m] long, and it has many functions. In water, for instance, the beaver’s tail acts as a rudder for navigation. On land it is used for stability as the beaver gnaws away at trees. When danger looms, the beaver slaps its tail on the surface of the water, alerting all beavers within earshot to head for safety. To clear up one misconception, though, the beaver does not use its tail as a mason’s trowel to apply mud to its dams.
Food and Water
What does a beaver eat? The tender inner bark and the buds of poplar and willow trees are at the top of its menu. Hence, while cutting down a tree for a building project, the beaver can also enjoy a hearty meal. Sometimes while one beaver is busy chipping away at a trunk, another will sneak up and steal some tasty bark from the other’s blind side.
During winter the beaver utilizes a unique food-storage system. First, it will dig a deep hole underwater—a feat that is not too difficult, since the beaver can remain submerged for 15 minutes at a time. Then, the beaver piles branches of aspen, willow, and other trees on the surface over the hole. As more wood is piled on, the stack eventually reaches the bottom of the hole. Later, when ice encases the pond and snow impedes surface activity, the colony has a well-stocked underwater “pantry.”
Speaking of water, few land animals are as comfortable in it as the beaver. Besides its dense fur, which is waterproofed with oil, the beaver also has a layer of subcutaneous fat that provides it with insulation in the coldest water. Why, beavers even mate underwater! Since water plays such a prominent role in the life of beavers, you will never find them living far from lakes and streams.
Beavers and Humans
Beavers are docile, and they readily befriend humans who treat them kindly. The animals groom themselves regularly and keep themselves clean. In bygone days, Native Americans often kept beavers as pets around their campsites. You will want to think twice, though, before letting a beaver into your home. The problem is that they never stop building. “When kept indoors,” writes environmental engineer Alice Outwater, “they will cut down the legs of tables and chairs and build little dams between pieces of furniture.” Trees and fence posts in the backyard might suffer a similar fate.
But even more serious problems have arisen between beavers and people. For example, some landowners complain that dams cause streams to rise, resulting in damage to property. However, scientists and others counter such complaints by pointing out the benefits of beaver activity. For example, the water-impounding work of beavers conserves and purifies water and provides life-sustaining conditions for many species. Some even say that beaver ponds have reduced the effects of drought.
Naturalists estimate that about 10,000,000 beavers now live in the continental United States. However, some estimate that more than 200,000,000 were living in that same area 500 years ago. Just think: Tens of millions of “lumberjacks” may have been working in the forests of North America before the first Europeans arrived. Yet, instead of finding a barren land devoid of trees, those early settlers beheld vast, flourishing forests. Clearly the beaver plays an important role in the ecology of our planet. Thus, we can be thankful that the original lumberjack is still on the job!
[Box/Picture on page 22, 23]
“Busy as a Beaver”
The person who coined that phrase had likely observed beavers at work damming a stream or building their home. Indeed, these animals seem tireless as they cut trees and haul the pieces to the construction site. At times, they even dig canals for floating building materials to the proper location.
But how do beavers build their dams? First, to anchor the structure, they set branches into the bottom of the stream. If the course is wide, the beavers bow their embankment upstream to strengthen it against the current. Using more wood, they fill the span up to the proper height, and then they stop up holes with mud and stones. To make the dam sturdy, the beavers will brace it on the downstream side by setting branches into the streambed at an angle. These industrious creatures even make regular repairs to their handiwork!
A tranquil pond soon forms upstream. Here the beavers build secure living quarters—first a simple burrow in the riverbank while the dam is under construction and later an offshore, domed lodge of mud and sticks. To guard against predators, the beavers use underwater entrances. Safe inside, they rest and raise their young.
The beaver is truly industrious. Scientists in Wyoming, U.S.A., released ten beavers—five male and five female—in an area where none had been seen for a long time. A year later, the researchers returned to find that they had established five distinct colonies and had built 55 dams!
[Pictures on page 24]
A beaver at work; a beaver lodge and dam; a baby beaver