The beaver floated with its head sticking up out of the water and just stared at me. In the early twilight, the beaver’s constant presence was menacing. It clearly wanted the pool to itself and was willing to stay within a short distance of my fly rod and me until I packed up and left. Negotiation about who would use the pool seemed out of the question.
The beaver is usually thought of as an animal that lives in a lodge in the center of a pond formed behind a stick dam. But that is not always the case, as I discovered while being evicted from the promising-looking trout stream. Beaver also live in dens dug into riverbanks where no dam is required. A dam is only built to insure that the water is deep enough for underwater habitat to remain unfrozen below the ice throughout the winter. The deep water of a river pool may provide the necessary storage for winter food as well as secure, underwater access to the den, safe from predators.
The beaver is the largest rodent in North America. The scientific name, Castor canadensis, refers to the castor glands located near the base of the tail. Castor is a strong-smelling, oily substance that beaver spread across their fur while preening to waterproof their outer coat.
Beavers may live up to 12 years, growing throughout their lives, sometimes reaching four feet from nose to base of tail and as much as 100 pounds in weight. Their ancestors were even larger: one million years ago, during the Pleistocene, the era of the mastodons and mammoths, the beavers that inhabited North America measured just under nine feet and weighed as much as 800 pounds. Fortunately, the beaver contesting my fishing pool was much smaller than that.
The beaver has a rotund body, short legs, and is ungainly on land. When threatened, it travels in an awkward bounding gallop, and in a chase over any distance, a predator can usually run a beaver down. If cornered, a beaver will defend itself by standing on its hind legs, hissing or growling, and lunging at its attacker. Given their sharp incisor teeth, beavers can put up a spirited defense, but bears, wolves, and coyotes can all take beaver.
Not so in the water. The beaver is a strong swimmer, attaining speeds up to five miles per hour. Thanks to a transparent membrane drawn over the eye while swimming, beavers can see as well under water as on land. The keys to the beaver’s speed are large hind feet with five webbed toes on each. These hind feet provide the propulsion, with the tail being used only for occasional steering. Its forepaws are small, without webs, and the five front toes end in sharp claws. These paws are dexterous and carry the sticks and mud that beaver use in their construction projects.
The size of a den depends on family size and number of years of occupation. A beaver takes one mate for life. A litter, averaging three kits, is born each spring following a 100-day gestation period. Both parents care for the kits. Although the kits are furred, have teeth, and can see, walk, and swim when born, they generally don’t venture out of the lodge for at least a month. Any yearlings living in the lodge act as babysitters for the new litter.
Two-year-olds leave home each spring to find their own territories. Beavers rarely overpopulate any specific area because they decrease their rate of reproduction when their numbers exceed available food. With two-year old beavers always searching for new territory, however, population pressure can push these youngsters into occupying marginal habitat.
While some beaver behavior is instinctive, beavers also learn by experience, according to Dr. Donald Griffin, a noted researcher in animal cognition. I observed just such a case during a spring fishing trip on the White River. Although the warm spring sun had melted the ice toward the middle of the river, the edges were still ringed with ice. The beaver I saw was obviously tired of winter – it would swim to the ice, chisel out a dinner-plate-sized piece with its teeth, push it into the center of the river, and then bash it with its tail. After three hard whacks it would turn, inspect its handiwork and, if satisfied, go bite off another piece of ice and do it again.
Which reminded me of the beaver that had talked me out of my fishing pool. As I turned to go that night, I heard the beaver gently slap its tail once against the water. Three other members of its family, including two kits, soon appeared, ready to enjoy the evening in the now-quiet stream.