Sunday, September 14, 2008

A few notes about beavers in general

This photo shows a birch tree about 10 inches in diameter cut down by beaver (using their large front, or incisor, teeth) several years ago close to the Zealand Trail and the beaver pond in the photo below. The following is a concise natural history of the beaver that might be interesting if you know nothing about them.

Beaver have an immense 'range' and are found everywhere in North America from the Arctic to the Sonoran Desert. They're the largest rodents on the continent and have a history going back 30 million years in the fossil record. Modern beaver has been around for more than a million years but probably less than 4 million years. The latin 'genus' name for beaver is Castor (thus Castor Oil). The full latin name of our North American beaver is Castor canadensis There is one other species of beaver that is related to our C. canadensis and is native to Europe. Modern beavers can be six feet long, counting the tail, and weigh 50-65 pounds but the average adult size is more like 40 inches long, including the tail which is nominally 10 inches long, and a weight of around 35 pounds. The babies are referred to as 'kits'. Beavers live in a semi-aquatic environment (meaning near but also under water) but can be terrestrial and live in burrows that they dig themselves such as beaver who live in the Sonoran Desert region of the southwestern United States. Beaver's front paws are incredibly adept at many tasks including fine manipulations of objects (cameras, cell phones?). Their hind feet are webbed for swimming. Their eyes, mouth, and ears have protective membranes that allow them to stay for long periods, and see and chew underwater. Beavers are vegetarians, or 'herbivorous' and eat bark of trees like aspen, poplar and willow, and birch. Like many rodents the beaver is incredibly versatile and able to adapt to myriad environments. The most notable aspects of beaver is 1.) their proclivity to stop moving water and impound it behind dams wherever they can, and 2.) their fur. They have two layers of fur, a grayish bottom layer next to the skin made of really thick fur that acts as super insulation, and a second layer of coarse brown colored fur sometimes referred to as "guard hairs". The beaver active in the White Mountains are typical, modern beaver. They live in lodges that provide amazing protection from predators as well as warmth in the winter months. They are typically called 'nocturnal' meaning they're active at night but they're also seen during the late afternoon and early evening and in the early morning as well. They live in extended families, or colonies, which typically have up to a 8-10 individuals with at least 2 of them a mated pair of adults. Beavers mate for life and could be considered matriarchal as the female manages the colony. If the male dies the female will take in another male. If the female dies the dam and lodge are abandoned. It may be the case in the Zealand Valley that the colony's female died and the pools and lodges have been abandoned. The picture above shows a beaver cutting that's several years old. There are no new cuttings that would indicate current activity. When beavers overpopulate an area and are considered a public nusance trapper are sometimes contracted to "cull" the beaver which means trap and kill them. This was the case at Lonesome Lake a few years ago where there was an active beaver colonly. Beavers and human are sometimes at odds but from the early 1600s and until the late 1800s, the period when top hats, made from beaver skins, were fashionable in Europe, beavers were at odds with humans and were nearly killed to extinction. As soon as Europeans arrived in North America they began trapping beaver from a starting population probably in the millions reducing it to very nearly to zero, as was reported in Maine and New Hampshire, in just a few decades. The beaver skins, of course, were valuable. One last note of interest: in the summer of 1963, right around sunset, I found a female beaver on the summit of Mt. Washington, at 6, 288 feet above sea level, heading east to west and about to descend into Ammonoosuc Ravine. She was trapped by some Fish and Game personel and taken to a location unknown. Her migration is interesting to note if only because Mt. Washington, basically a rock pile a mile high, would be an arduous hike for a beaver, I would imagine, but this one was undetered and dramatized their determination and strength.

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