Friday, June 10, 2011

Beavers (Busy Introduction)


North American Beaver (Castor canadensis)

I.  "A state game official calls last week’s rabid beaver attacks in Philadelphia 'bizarre' as they remain stumped about the rogue rodents.  'It's not that beavers are not susceptible, as all mammals are susceptible, to rabies,' said commission spokesman Jerry Feaser. 'But a beaver in Philadelphia, that was just truly bizarre.' * Another rabid beaver attacked an angler in late April on White Clay Creek in the Chester County suburbs of Philadelphia. Feaser said the attacks are the only such cases he recalls during 12 years with the commission. 'Our furbearer biologist, when he heard about this, he was just literally blown away,' Feaser said."

II.  The beaver (genus Castor) is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver (Castor canadensis) (native to North America) and Eurasian Beaver (Castor fiber) (Eurasia). Beavers are known for building dams, canals, and lodges (homes). They are the second-largest rodent in the world (after the capybara). Their colonies create one or more dams to provide still, deep water to protect against predators, and to float food and building material. The North American beaver population was once more than 60 million, but as of 1988 was 6–12 million. This population decline is due to extensive hunting for fur, for glands used as medicine and perfume, and because their harvesting of trees and flooding of waterways may interfere with other land uses.

Beaver dam in Algonquin, Ontario

III.   Beavers are known for their natural trait of building dams on rivers and streams, and building their homes (known as "lodges") in the resulting pond. Beavers also build canals to float build materials that are difficult to haul over land.  They use powerful front teeth to cut trees and other plants that they use both for building and for food. In the absence of existing ponds, beavers must construct dams before building their lodges. First they place vertical poles, then fill between the poles with a crisscross of horizontally placed branches. They fill in the gaps between the branches with a combination of weeds and mud until the dam impounds sufficient water to surround the lodge.

Beaver lodge (from David Darling)

IV.  Beavers are are known for their alarm signal: when startled or frightened, a swimming beaver will rapidly dive while forcefully slapping the water with its broad tail, audible over great distances above and below water. This serves as a warning to beavers in the area. Once a beaver has sounded the alarm, nearby beavers will dive and may not reemerge for some time. Beavers are slow on land, but are good swimmers, and can stay under water for as long as 15 minutes.

Beaver tail-slap 

V.  Beavers are herbivores, and prefer the wood of quaking aspen, cottonwood, willow, alder, birch, maple and cherry trees. They also eat sedges, pondweed, and water lilies.

Quaking Aspens, Little Cottonwood Canyon, Salt Lake County, Utah

VI.  Beavers do not hibernate, but store sticks and logs in a pile in their ponds, eating the underbark. The word is descended from the Proto-Indo-European name of the animal, cf. Sanskrit babhru's, brown, Lat. fiber, Ger. Biber, Russ. bobr; the root bhru has given "brown", and, through Romanic, "bronze" and "burnish". 

VII. The beaver works as a "keystone species" in an ecosystem by creating wetlands that are used by many other species. Next to humans, no other extant animal appears to do more to shape its landscape.

Beaver in wetlands

VIII.  Beaver dams are created as a protection against predators, such as coyotes, wolves and bears, and to provide easy access to food during winter. Beavers always work at night and are prolific builders, carrying mud and stones with their fore-paws and timber between their teeth. Because of this, destroying a beaver dam without removing the beavers is difficult, especially if the dam is downstream of an active lodge. Beavers can rebuild such primary dams overnight, though they may not defend secondary dams as vigorously. (Beavers may create a series of dams along a river.)

IX. The ponds created by well-maintained dams help isolate the beavers' homes, their lodges, which are created from severed branches and mud. The beavers cover their lodges late every autumn with fresh mud, which freezes when the frost sets in. The mud becomes almost as hard as stone, and neither wolves nor wolverines can penetrate it.The lodge has underwater entrances to make entry nearly impossible for any other animal (however, muskrats have been seen living inside beaver lodges with the beavers who made them).  A very small amount of the lodge is actually used as a living area. Contrary to popular belief, beavers actually dig out their dens with underwater entrances after they finish building the dams and lodge structures. There are typically two dens within the lodge, one for drying off after exiting the water, and another, drier one where the family actually lives.

Beaver pond, Lundy Lake, California (beaver lodge in center)

X.  Much of the early exploration and trade of Canada was based on the quest for beaver. The most valuable part of the beaver is its inner fur whose many minute barbs make it excellent for felting, especially for hats. In Canada a "made beaver" or castor gras that an Indian had worn or slept on was more valuable than a fresh skin since this tended to wear off the outer guard hairs.

General map of the "Beaver Hunting Grounds" described in "Deed from the Five Nations to the King", the 1701 Nanfan Treaty made between representatives of the Iroquois Confederacy and John Nanfan, the acting colonial governor of New York, on behalf of The Crown.  The treaty was conducted in Albany, New York on July 19, 1701, but was not ratified until September 14, 1726.  Because the vast majority of the Beaver Hunting Grounds described in the Nanfan Treaty were located in New France, the French did not recognize the treaty as valid.

XI.  In wider culture, the beaver is famed for its industriousness. The English verb "to beaver" means to work hard and constantly.

XII.  In the 17th century, based on a question raised by the Bishop of Quebec, the Roman Catholic Church ruled that the beaver was a fish (beaver flesh was a part of the indigenous peoples' diet, prior to the Europeans' arrival) for purposes of dietary law. Therefore, the general prohibition on the consumption of meat on Fridays during Lent did not apply to beaver meat. The legal basis for the decision probably rests with the Summa Theologica of Thomas Aquinas, which bases animal classification as much on habit as anatomy. This is similar to the Church's classification of the capybara, another semi-aquatic rodent. 

A group of capybaras sitting at the edge of a bank, watching one of the other capybaras jump into the water.

XIIIIn computability theory, a busy beaver (from the colloquial expression for "industrious person") is a Turing machine that attains the maximum "operational busyness" (such as measured by the number of steps performed, or the number of nonblank symbols finally on the tape) among all the Turing machines in a certain class.

Three-state "busy beaver" Turing machine

Alan Turing (1912-54)

Busy Beaver puts another one on the Turing Machine's tape.

XIV.  Beavers have been trapped for millennia, and this continues to this day.

Early French-Canadian "Lane" beaver trap

XV. Beaver pelts were used for barter by Native Americans in the 17th century to gain European goods. They were then shipped back to Great Britain and France where they were made into clothing items. Widespread hunting and trapping of beavers led to their endangerment. Eventually, the fur trade declined due to decreasing demand in Europe and the takeover of trapping grounds to support the growing agriculture sector. A small resurgence in beaver trapping has occurred in some areas where there is an over-population of beaver; trapping is done when the fur is of value, and the remainder of the animal may be used as feed. In the 1976/1977 season, 500,000 beaver pelts were harvested in North America.

"Beaver hats served as a status symbol for position and wealth from the 1600s to the mid-1800s. It is impossible to estimate the number of beaver plews auctioned off in England during the fur trade era. It is generally thought by 1840 the beaver era was over, but Hudson’s Bay Company records show three million beaver pelts were sold in London between 1853 and 1873. Despite the French and French-Canadian's early domination of the fur trade, the majority of beaver hats were made in England."   

Portrait of George Fox (1838 engraving by S. Allen based on an earlier painting by S. Chinn)

* Reader NoteSeveral recent press articles in the press concerning the status of the beaver in the Commonwealth of Pennsylvania, including the one summarized in I. above reporting a couple of recent, highly unusual beaver attack incidents in the Philadelphia area, aroused my dormant latent  interest in learning more about the beaver, the world's second-largest rodent.  

         I had never actually seen a beaver in the wild until two days ago when I saw one cross our property twice.  At first I thought he was a raccoon or a groundhog, but I stopped to get a good look and "Eureka!".  

         Several years ago an old friend (I think), a college professor who is a highly respected dam history and technology expert, showed me one of his final exam questions, which read: "Beaver dams:  Pastoral or monumental?"  In typical academic trick-speak, the correct answer is: "Both."  Still, I think it's a good question.

         There is so much more to say about beavers and I do not mean for a minute to ellide over the tragedy of beaver hunting and killing, a big and important story.  This world is a vale of tears.  Acts of unnecessary personal cruelty and petty discourtesy (to keep in practice, I suppose) are the norm.  More and more I realize this. Less and less am I able to discern why. 

         I recall, however, George Fox's Journal:  

         "And when all my hopes in them and in all men were gone, so that I had nothing outwardly to help me, nor could I tell what to do; then, oh then I heard a voice which said, 'There is one, even Jesus Christ, that can speak to thy condition', and when I heard it, my heart did leap for joy."