From time to time, Ferrebeeekeeper indulges in a theme week.  Last Halloween featured Greek Monster Week, which highlighted the mythical spawn of Echidna, the great serpent mother of classical mythology.  Other theme weeks have included Tree Week and Small Furry Animals Week (which described the groundhog, the pika, the hyrax, the rabbit, and the wombat).  In order to combat malaise in the world construction markets, Ferrebeekeeper now presents Builders Week, five posts dedicated to great builders and the edifices they have created.  To start off the week, this post is dedicated to the beaver, the most accomplished and tireless builder of the animal kingdom–save perhaps for corals, termites, and humans.  Not only is the busy building beaver a keystone species to ecosystems around the Northern hemisphere, the furry rodent holds a key place in American history.

Eurasian Beavers (Castor fiber) photo by zooadmin

There are two species of beaver, the North American beaver (Castor Canadensis) and the Eurasian beaver (Castor fiber).  Although similar in appearance and habit, the two species are not genetically compatible and, when mated, do not produce living offspring.  Like the other giant rodents (capybara, nutrias, etc) beavers are semi aquatic and spend nearly as much time in the water as on land. In order to get around on land and water, beavers have webbed clawed feet and a flat, hairless paddle-like tail.  Their ears and nostrils clamp shut under water and a special membrane snaps over their eyes.  In order to keep warm in harsh northern winters, beavers have a layer of subcutaneous fat as well as a dense coat which they waterproof with oily castoreum (produced from a scent gland).  To round out their special features, beavers possess formidable upper and lower incisors with which they gnaw down trees. Adult beavers can weigh up to 30 Kilograms (about 60 pounds) and attain lengths of 1.3 meters (about 4 feet).

North American Beaver (Castor canadensis)

Beavers are intelligent animals which form close family bonds. According to the website Beaver: Wetlands and Wildlife:

Wildlife rehabilitators find beavers to be gentle, reasoning beings who enjoy playing practical jokes…. Beavers mate for life during their third year. Both parents care for the kits (usually one to four) that are born in the spring. The youngsters normally stay with their parents for two years, and the yearlings become babysitters for the new litter. After weaning, their favorite foods include water lily tubers, apples and the leaves and green bark (cambium) from aspen and other fast-growing trees.

Above all, the beaver is a masterful builder capable of cutting down large trees and moving them into place to serve as the foundation of a dam.  Reinforced with mud, and “planted” with living green shoots (which grow into the structures and thus add stability), beaver dams curve backwards against the current and are capable of holding immense volumes of water. Not only do beavers fell trees and create timberworks and earthworks, the creatures also excavate canals to provide a quick escape into the artificial lakes produced by their dam building. Within these lakes the beavers build lodges as escape shelters and winter homes.

Cross-section of a Beaver Lodge (DEA Picture Library/De Agostini Picture Library)

Such lodges can only be entered through hidden underwater entrances.  Crafted in sprawling mounds from logs, branches, and mud, the structures contain rooms for dying off and rooms for habitation.  Before winter the beavers coat their lodges with mud which freezes into a hard coat which makes the structures impervious to bears and wolverines. Beavers harvest tender shoots from their favorite softwoods and embed them deep in the mud of the coldest deepest part of their lakes.  In winter when the top of the lake is frozen, the animals can dive down and retrieve food from their underwater refrigerator.

The Largest Known Beaver Dam Photographed from Space

Beavers are ambitious in their work. To date the largest beaver dam discovered was over 850 meters in length (2,790 feet)–more than twice the width of Hoover Dam. Located in the forests of Alberta in Canada the huge dam was spotted from space via Google Earth.

The flooded lands formed by these dams provide a habitat for waterfowl, turtles, frogs, and other aquatic creatures (as well as protected nurseries for salmon fry). Additionally the dams alleviate flooding, allow the water table to recharge, and act as filters which soak up nitrogen and chemicals.  Some writers have (poetically?) described beaver dams and related lakes as the kidneys of a watershed. Since beaver dams are depositional environments, they silt up into rich bottom land when abandoned by their builders. This process is vital to forests and rivers in North America and Europe, where soft quick growing trees have evolved to deal with beavers’ appetite and industry. However beavers have caused disastrous flooding and environmental mayhem when furriers introduced them to areas (like Tierra del Fuega) where trees do not coppice.

The Fur Trade

Furriers have a long dark history with the beaver. Eurasian beavers were over-harvested to the point of near extinction by medieval trappers for their lustrous coats.  When the New World was being conquered and colonized by European nations, the valuable fur of North American beavers was one of the first economic incentives for exploration.  Trappers, traders, and runners-of-the-woods traveled deep into North America for the pelts of all manner of creatures: but they sought beaver hides foremost.  The dense fur was ideal for making the fashionable flamboyant hats of the seventeenth and eighteenth centuries (additionally beavers were classified as fish by the Catholic church and their flesh had special allure for hungry devout French trappers during Friday fasts). Competition between French and English fur traders for the pelts from the territory between the Alleghany Mountains and the Mississippi combined with long brewing national conflict to start the French and Indian War which in turn determined the course of civilization in North America.