A Good Day To You Sir

by Mitch Shindelbower

Title

A Good Day To You Sir

Artist

Mitch Shindelbower

Medium

Photograph

Description

The North American beaver (Castor canadensis) is one of two extant beaver species. It is native to North America and introduced to Patagonia in South America and some European countries (e.g., Norway). In the United States and Canada, the species is often referred to simply as "beaver", though this causes some confusion because another distantly related rodent, Aplodontia rufa, is often called the "mountain beaver". Other vernacular names, including American beaver[2] and Canadian beaver,[6] distinguish this species from the other extant beaver species, Castor fiber, which is native to Eurasia.
This beaver is the largest rodent in North America and the second or third largest rodent in the world, after the South American capybara. The species' Eurasian counterpart, the European beaver reaches similarly large sizes. Adults usually weigh from 11 to 32 kg (24 to 71 lb), with 20 kg (44 lb) being a typical mass. The head-and-body length is 74–90 cm (29–35 in), with the tail adding a further 20–35 cm (7.9–13.8 in). Very old individuals can exceptionally exceed normal sizes, weighing more than 40 kg (88 lb) or even as much as 50 kg (110 lb).[7][8][9][10]

Like the capybara, the beaver is semi-aquatic. The beaver has many traits suited to this lifestyle. It has a large flat paddle-shaped tail and large, webbed hind feet reminiscent of a human diver's swimfins. The unwebbed front paws are smaller, with claws. The eyes are covered by a nictitating membrane which allows the beaver to see underwater. The nostrils and ears are sealed while submerged. A thick layer of fat under its skin insulates the beaver from its cold water environment.

The beaver's fur consists of long, coarse outer hairs and short, fine inner hairs (see Double coat). The fur has a range of colours but usually is dark brown. Scent glands near the genitals secrete an oily substance known as castoreum, which the beaver uses to waterproof its fur.

Before their near extirpation by trapping in North America, beaver were practically ubiquitous and lived from the arctic tundra to the deserts of northern Mexico, and from the Atlantic to the Pacific Oceans.[11][12] Physician naturalist Edgar Alexander Mearns' 1907 report of beaver on the Sonora River may be the southernmost extent of the range of this North American aquatic mammal.[13] However, beaver have also been reported both historically and contemporaneously in Mexico on the Colorado River, Bavispe River and San Bernardino River.[14]
Skull of a North American Beaver found on San Francisco Bay shore
Behaviour
Beaver lodge, Ontario, Canada
Beaver dam, northern California, USA

Beavers are mainly active at night. They are excellent swimmers and may remain submerged for up to 15 minutes. More vulnerable on land, they tend to remain in the water as much as possible. They use their flat, scaly tail both to signal danger by slapping the surface of the water and as a location for fat storage.

They construct their homes, or "lodges," out of sticks, twigs, rocks and mud in lakes, streams, and tidal river deltas.[15] These lodges may be surrounded by water, or touching land, including burrows dug into river banks. They are well known for building dams across streams and constructing their lodge in the artificial pond which forms. When building in a pond, the beavers first make a pile of sticks and then eat out one or more underwater entrances and two platforms above the water surface inside the pile. The first is used for drying off. Towards winter, the lodge is often plastered with mud which when it freezes has the consistency of concrete. A small air hole is left in the top of the lodge.

The dam is constructed using logs from trees the beavers cut down, as well as rocks, grass and mud. The inner bark, twigs, shoots and leaves of such trees are also an important part of the beaver's diet.[16] The trees are cut down using their strong incisor teeth. Their front paws are used for digging and carrying and placing materials. Some researchers have shown that the sound of running water dictates when and where a beaver builds its dam. Besides providing a safe home for the beaver, beaver ponds also provide habitat for waterfowl, fish, and other aquatic animals. Their dams help reduce soil erosion and can help reduce flooding. However, beaver dams are not permanent and depend on the beavers' continued presence for their maintenance. Beavers generally concentrate on building and repairing dams in the fall in preparation for the coming winter. In northern areas they often don't repair breaches in the dam made by otters, and sometimes breach the dam themselves and lower the water level in the pond in order to create more breathing space under the ice or get easier access to trees below the dam. In a 1988 study in Alberta, Canada, no beavers repaired "sites of water loss" during the winter. Of 178 sites of water loss, beavers repaired 78 when water was opened, and did not repair 68. The rest were partially repaired.[17]

Beavers are most famous, and infamous, for their dam-building. They maintain their pond-habitat by reacting quickly to the sound of running water, and damming it up with tree branches and mud. Early ecologists believed that this dam-building was an amazing feat of architectural planning, indicative of the beaver's high intellect. This theory was questioned when a recording of running water was played in a field near a beaver pond. Despite the fact that it was on dry land, the beaver covered the tape player with branches and mud.[18] The largest beaver dam is 2,790 ft (850 m) in length—more than half a mile long—and was discovered via satellite imagery in 2007.[19] It is located on the southern edge of Wood Buffalo National Park in northern Alberta and is twice the width of the Hoover Dam which spans 1,244 ft (379 m).[20]
C. c. canadensis, feeding in winter

Normally, the purpose of the dam is to provide water around their lodges that is deep enough that it does not freeze solid in winter. The dams also flood areas of surrounding forest, giving the beaver safe access to an important food supply, which is the leaves, buds, and inner bark of growing trees. They prefer aspen and poplar, but will also take birch, maple, willow, alder, black cherry, red oak, beech, ash, hornbeam and occasionally pine and spruce.[21] They will also eat cattails, water lilies and other aquatic vegetation, especially in the early spring (and contrary to widespread belief,[22] they do not eat fish). In areas where their pond freezes over, beavers collect food in late fall in the form of tree branches, storing them underwater (usually by sticking the sharp chewed base of the branches into the mud on the pond bottom), where they can be accessed through the winter. Often the pile of food branches projects above the pond and collects snow. This insulates the water below it and keeps the pond open at that location.

Beavers usually mate for life. The young beaver "kits" typically remain with their parents for up to two years.
Brooklyn Museum - American Beaver - John J. Audubon

Common natural predators include gray wolves, coyotes, and mountain lions. Beaver can be particularly important food for lone wolves.[23] American black bears may also prey on beavers if the opportunity arises, often by smashing their paws into the beaver's lodges.[24][25][26] Perhaps due to differing habitat preferences, Brown bears were not known to hunt beavers in Denali National Park.[27] Less significant predators include wolverines, Canadian lynx, bobcats, and fox, which are increasingly unlikely to take full-grown beavers due to their smaller size, and American alligators, which only minimally co-exist with beavers. Both Golden Eagles (Aquila chrysaetos) and Bald Eagles (Haliaeetus leucocephalus) may on occasion predate a beaver, most likely only small kits.[28] Despite repeated claims there is no evidence that river otters are predators of beavers.[29]
Reproduction

North American beaver have one litter per year, coming into estrus for only 12 to 24 hours, between late December and May but peaking in January. Unlike most other rodents, beaver pairs are monogamous, staying together for multiple breeding seasons. Gestation averages 128 days and they average two to three kits per litter with a range of two to six kits.[30] Most beaver do not reproduce until they are three years of age, but about 20% of two-year-old females reproduce.

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January 26th, 2014

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