Beaver

Name

The beaver (Castor canadensis) gets the first part of its scientific name from the castor glands under the skin between its hind legs. These occur in both male and female.

This semi-aquatic furbearer was of great significance in the early exploration and settling of Canada. Its pelt attracted men such as Champlain, Radisson and des Groseilliers who, in their search for furs and fur-trading territories, influenced the course of Canadian history. New territories in the northwest were opened up as a result of the European demand for furs and, in 1670, the Hudson’s Bay Company established the northern fur trade.

Because of its key role in Canadian history, the beaver has become a national emblem depicted on stamps, coins and souvenirs.

Distribution

Native to Canada and the United States, the beaver is found across both countries wherever there are streams and deciduous trees. Beaver live as far north as the mouth of the MacKenzie River on the Arctic Ocean and as far south as northern Mexico. They are also found in northern Europe, and have been introduced to South America.

Description

The beaver appears clumsy on land, but is agile in the water. It is well equipped for the semi-aquatic life it leads. Its scaly, paddle-shaped tail is used for swimming and diving, to signal alarm, and to maintain balance when the beaver is felling trees. The tail also stores fat to provide energy in winter, and regulates body temperature by dispelling heat. Muscular contractions of the nostrils and ears prevent water from being inhaled and from causing ear damage when the beaver dives. Fur-covered lips behind the front incisors allow it to chew under water. Because the brain is able to redirect oxygen from the stomach area and from the legs and tail to essential organs such as the heart, the beaver can remain submerged for up to 15 minutes. In winter, it can obtain oxygen from air bubbles and air spaces under the ice. Its pelt provides protection from moisture and cold. The hind paws are large and webbed for swimming.

Other adaptations of the beaver include short front legs with forepaws capable of manipulating twigs, and toenails suitable for digging. The second claw on each hind paw is split to make grooming easier.

Although the beaver’s eyes are small and weak, its sense of hearing and smell are acute.

One of the largest rodents on earth, the beaver weighs between 18 and 22 kg (40 to 50 Ibs.) when mature. Some individuals may weigh even more, but beaver of more than 27 kg (60 lbs.) are rare in Ontario.

The thick brown coat consists of two types of hair. The outer guard hair is long, stiff and thick. The shorter, denser underfur provides insulation. Each guard hair has a special muscle that can erect the hair to increase the fur density and insulating ability.

The quality of the fur is determined by evaluating its density and colour. The pelt is prime in late fall and early winter. By late winter, the fur is no longer prime and may be described as "springy" or "rubbed"; it is "springy" when the underfur begins to shed, and "rubbed" when the guard hairs are worn off. Although the beaver appears shiny and well furred in summer, the underfur necessary to a prime pelt is not present until the return of cold weather.

Life History

Beaver mate for life and will take another mate only if the first is killed. The female produces her first litter at the age of two or three. Breeding takes place in the water between January and March, and the young are born between May and July after a gestation period of 110 days. The size of the litter varies according to the food supply, population density and the age of the female. The number of young in her litter increases annually until the female reaches the age of six or seven. The average litter contains from three to five kits.

The young are born fully furred and with their eyes open. They are able to swim at birth. The kits nurse from eight to ten weeks, and the female spends most of this time with them in the lodge. By fall, the young are able to help gather the winter food supply. They may leave the family colony by their first birthday, and may be gradually forced out by their parents, if they have not left by the age of two.

In some areas, males outnumber females at the kit stage, but later the ratio of males to females is equal. The average lifespan of beaver in the wild is from four to five years. Between 70 and 80 per cent of kits die by 12 months of age. Age can be determined by examining the root tips of the four side teeth in the lower jaw. As the beaver ages, the opening at the root tip becomes sealed. Annual layers in the teeth, like tree rings, also indicate age.

Habitat

Beaver cannot live where the water is polluted, or is too shallow or too rapid. However, they can live in areas where the food supply is poor. Where food is scarce or of poor quality, birth rates are low and mortality rates high. Ideal beaver habitat consists of slow, meandering streams and creeks bordered by trembling aspen, or small lakes with shallow, muddy bays in which lodges can be built and with deciduous trees and shrubs near shore. Ponds with streams running into or out of them are other common lodge sites.

Beaver change their habitat to suit their needs, and their dams can drastically alter the landscape. Each colony may build a series of dams on a stream, causing the water to back up and increasing the depth and surface area. The flooding which results allows the beaver to fell trees, which were formerly too far from shore, and ensures adequate water depth for winter. The beaver pond provides habitat for a variety of species including ducks, muskrat, mink, otter, moose and deer. Some beaver ponds support speckled trout until such time as the water becomes stagnant and too warm.

Food and Feeding Behaviour

Beaver will eat any kind of tree or shrub. They prefer aspen or, if aspen is not available, red maple. Alder is used as building material. In Ontario’s far north, beavers eat willows. Other sources of food in the spring and summer include tree bark, duckweed, pond lily leaves, grass, bracken fern and the roots of aquatic plants.

Food conditions in a particular area may be evaluated by examining the colony’s winter food pile. If evergreens, oak and elm are found, conditions are considered poor. If the food under the top layer of alder consists largely of aspen, conditions are good.

Several unique adaptations aid in the digestion of wood and bark. The beaver has special glands associated with the stomach, and a pre-digestion chamber called the "appendix". Like rabbits, beaver practise coprophagy, the eating of their own droppings. This allows the digestive system to extract all of the nutrients from the wood. Beaver gnash their top and bottom incisors together so that their teeth, which are constantly growing, are kept worn down and sharp.

Habits

Beaver colonies contain from two to 12 members. A typical established colony has one breeding pair and a number of yearlings and kits. Territorial by nature, beaver will attack other beaver if they trespass. Territories are maintained by the use of scent mounds or "pads" which consists of piles of dirt covered with a yellow-orange substance secreted by the beaver’s castor glands. These glands, which weigh up to 93 gm (4 oz), are used by the perfume industry.

The most familiar handiwork of the beaver is the dam, which is constructed of sticks and branches that are dragged to the site, piled and interwoven, and sealed on the upstream side with mud and stones. This activity is instinctive and will occur wherever beavers are stimulated to build by the sound of running water. If the water level in the beaver pond drops for any reason, the colony immediately sets about putting fresh mud on the dam in an attempt to remedy the situation. Beavers inhabit lodges or houses, which they construct from mud and sticks. These may be surrounded by water or located against the banks of lakes or streams. They are conical in shape and feature an unmuddied spot directly on top, which serves as an air vent. Houses provide protection and keep the colony warm in winter. Many colonies also construct tunnel systems in the banks of streams and ponds.

Although small trees can be felled easily by one beaver, large trees may require the co-operation of two or more beaver taking turns at the job. Contrary to popular belief, beaver cannot plan the direction in which trees will fall. Many trees become hung up in the branches of surrounding trees and are lost to the colony. In heavily forested areas, this loss may amount to one-half of the trees felled.

Beavers are most frequently active from dusk to morning. In winter, their activities are restricted to travelling under the ice between the house and the food pile.

Population Changes

Before the turn of the century, beavers were nearly wiped out by uncontrolled harvesting. Now, however, there are more beaver in Ontario than ever before. This reversal in the population trend appears to be due to the continued efforts to control the harvest and to the good habitat conditions available throughout the province.

Beavers have certain built-in safeguards that affect their numbers. They are very territorial, and only a certain number can be accommodated within a given area. Factors like food quality and the type of water available also have an effect on their numbers. Where habitat conditions are excellent, overpopulation can occur. If the population becomes too dense, habitat deteriorates and mortality rates increase.

Predators, parasites and most diseases have no significant effect on the beaver population. Only tularemia, a bacterial disease that produces white spots on the liver and spleen, can severely reduce their numbers. In the 1940s, the beaver population of northern Ontario almost disappeared because of a tularemia outbreak. Since this disease can be transmitted to humans, caution must be taken when dealing with animals suspected of having it.

Beaver may be host to at least six different internal parasites, none of which causes death. The roundworm (Dipetalonemia sprenti) is one common parasite, which inhabits the body cavity. It is thin, round, white and coiled, and measures from 5 to 11 cm (2 to 4.5 in). External parasites include ear ticks and two types of small beetle sometimes found in great abundance in the fur. None of these external parasites appears to damage the pelt.

Management

In the past, beaver management was based mainly on economic considerations. Today, it must also take into account the environmental and aesthetic needs of the people of Ontario. More is known about the beaver, and management techniques are more specific and sophisticated than those used to manage other furbearers. Yet, the task of managing beaver is complex, and must involve the co-operation of trappers, private landowners and government agencies. In the following sub-sections, some of the methods and problems of beaver management are presented.

A. Surveys

On Crown land, trapping is controlled by means of a registered trapline system. Each trapline has a yearly quota based on information acquired from past harvests and recent surveys conducted by local trappers in co-operation with the Ministry of Natural Resources.

A five-year program conducted in the Kirkland Lake District showed that trappers were able to increase their harvests by an average of 30 percent when their quotas were set on the basis of aerial surveys of the beaver houses on their traplines.

With an end to aerial surveys, trappers now conduct surveys of their own traplines. Surveys should be conducted immediately before freeze-up, after the leaves fall. At this time, beaver activity is at its peak and fresh feed beds, which are the most reliable signs that a colony intends to remain in the area over the winter, can be seen. Muddied water associated with the building of dams and houses can also be a sign of winter residency. Less reliable signs are used as evidence of established beaver colonies only if they are very abundant and are at a distance from other known beaver colonies. These signs include floating sticks, partly muddied houses, some cut trees, a dam, and partly flooded land. All beaver colonies located should be marked on a map that is kept for future reference.

B. Setting Quotas

There is as much danger in under-harvesting as there is in over- harvesting. If the beaver population becomes too large, there is a danger that the habitat will be damaged and the beaver will become more susceptible to diseases like tularemia. In Ontario, most beaver populations are under-harvested. Only 50 to 60 per cent of the allowed number are actually trapped. If a trapline is known to be under-harvested and the habitat is seen to be deteriorating, steps must be taken to reduce the beaver population by at least 30 per cent. In extreme cases, up to 50 per cent of the resident beaver must be removed.

To obtain a sustained harvest on most traplines, 30 percent of the beaver should be taken each year. Thus, the quota for any trapline would be 30 percent of the beaver thought to be living there. To get that figure, the number of beaver houses mapped in the survey is multiplied by the average number of beaver per house. Information on the ages of beaver taken in past harvests and the productivity of the colonies is also used in setting quotas. This can be obtained by examining the teeth, pelt sizes, embryos, and scars on the reproductive organs of the beaver harvest. Trappers are required to harvest at least 75% of the annual quotas set for their trapline.

C. Trapping on Private Land

Although the Ministry can set recommended harvest levels for privately owned lands, it is the landowners who control the harvest by determining whether access is granted to trappers. Trapping may take place on privately owned lands either during the trapping season or when local beaver colonies are causing a problem. Out of season problems can be kept to a minimum by co-operation between landowners and trappers to harvest beaver during the trapping season when pelts are prime.

Written permission from the landowner must be obtained before trapping begins. If the permission carries stipulations, these must be followed or the permission to trap can be revoked. In early spring and late fall, the trapper should check all ponds, creeks and springs on the property for signs of beaver activity. The landowner should be kept aware of the trapper’s progress.

Where beaver are creating a problem, the landowner is entitled under the Game and Fish Act to destroy them by any means and at any time of the year. It is preferable, however, that problem beaver be trapped during the season so that the maximum pelt price can be obtained. It is therefore to the trapper’s benefit to spot potential problems early and report them to the landowner. Beaver populations near railroads or public highways should be kept to a minimum. In cases in which the failure of a dam could cause a washout, the beaver population should be eliminated by trapping, and steps should be taken to prevent other colonies from being established at that location.