Many say that second only to man, the North American Beaver (Castor canadensis) is arguably the most prolific and successful adaptor of its environment. This remarkable rodent has a multitude of adaptations that enable it to engineer its surroundings and to overcome the challenges of climate and predation. Chester County is

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The maintenance of my dam keeps me busy as a beaver, yet the higher water makes it easier to reach and carry food.

currently home to thriving beaver colonies; however, this wasn't always the case.

HISTORY: The beaver and mankind have a long history of interaction. A pivotal figure in Native American culture, the beaver is referred to as "the Sacred Center of the Earth" due to its ability to create wetland habitat, which in turn supports many species of animals, aquatic life, insects and plants.

 

The first European settlers' westward expansion was driven and fuelled by the fur trade. This business boom did not afford the beaver the same level of reverence as Native Americans. During the 17th and 18th Centuries the beaver population suffered as the demands of European fashion prompted trapping at an increasing rate. Only a change of fashion in Europe saved the beaver. Silk from the Far East became the prized material and the market price for a beaver pelt fell rapidly.

Even so, the beaver was a long way from being safe. At the beginning of the Twentieth Century there were few beavers in Pennsylvania. In 1903 the State Legislature passed a law protecting the beaver, and in 1917 the Pennsylvania Game Commission released a pair in Cameron County. More pairs were reintroduced, which allowed the population to eventually flourish.  This wildlife management reversed the almost fatal decline of the beaver.

THE NORTH AMERICAN BEAVER belongs to the Order Rodentia and is the world's second largest rodent.  Beavers can grow up to 40" long, including the tail, and can weigh up to 60 lbs. Beavers have a lifespan of 10-15 years in the wild, and approximately 20 years in captivity. Beavers are herbivores, eating a wide array of plant materials from aquatic vegetation like lilies, grasses and leaves in spring and summer, with the cambium (the green layer found underneath the outer bark) of trees such as aspen, willow, birch and poplar in fall and winter.

 

HABITAT: Beavers select rivers, streams, ponds and lakes upon which to build their trademark dams and lodges. Beaver dams are constructed to raise the water level in the selected habitat so that a lodge, their primary shelter, can be surrounded by water. Tunnels accessing the lodge can be found beneath the surface. Beavers sometimes select sites that already have water deep enough to fulfill the underwater access requirement. Good examples of this are the lodges at the north end of Chambers Lake at Hibernia County Park. Beavers select habitats with a hearty supply of trees that provide both adequate building materials and a source of fall and winter food. Beavers also construct 'canals,' which they use to float materials from the felling location to the site of the lodge or dam.

 

A male beaver whose mate has given birth to her litter of kits sometimes builds a bank den as temporary shelter. Bank dens are sometimes built prior to the initial construction of a lodge. Beavers live in family groups called colonies. Each beaver lodge houses one colony that can comprise the adult mating pair, 2-3 yearlings born in the previous year, and 2-3 kits born in the current year.

ADAPTIONS:  Nature has provided the beaver with a toolbox of physical adaptations to help it survive the harshest climates. The most challenging time for beavers is during the winter when outside temperatures can fall to well below freezing.  Beaver fur has a dense underfur that serves as an insulator to cold air and water. Longer, coarser 'guard' hairs protect the underfur from dirt, and help the beaver to trap air bubbles that act as an additional source of insulation. This allows beavers to retrieve food materials from underwater food piles even when thick ice has formed around their lodges. During the fall beavers supplement their normal body fat to help insulate them from the cold winter water. They also reduce their average body temperature by a degree or two to conserve energy. To prevent excessive heat loss from blood circulating, beavers' feet and tails remain cold. This conserves warmth for the rest of their body.

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Timber! Beavers fell trees to get at the higher, newer, more succulent growth. Cutting this big tree also helps offset incisor growth to keep beaver teeth healthy.

Beavers have other special adaptations that help them cope with their water-based habitat. Their eyes have membranes that protect the eyeballs from debris and cold temperatures. These membranes slide over the eyeballs when the beaver submerges. Special valves in their noses and ears close to prevent water from getting in. Beavers can close their lips behind their incisor teeth, allowing them to chew, cut and carry materials while submerged. Beavers have short, powerful hind legs that provide the power to the webbed hind feet. These act as the primary method of propulsion under water. When under water a beaver's heart rate will drop to prolong the dive time. Most beavers can stay submerged for 15 minutes at a time, during which they can forage, work and play. To mark their territories, beavers excrete an oil called castoreum from castor sacs at the base of their tail onto mud piles. These are called scent mounds. Other glands excrete oil that is groomed into the fur to enhance waterproofing.

The beaver's most effective adaptation also permits it to adapt to its environment. Their prominent upper and lower incisors serve as primary cutters. These teeth are the primary tool used to fell trees, cut branches, gnaw through tough outer bark, and strip the cambium that lies under that bark. Beavers' incisors grow constantly, so they must gnaw and chew regularly to keep them from growing too long. The front surface of the incisor is covered with hard enamel, but the reverse surface is softer and wears down at a faster rate. This produces a chisel-like edge on the incisor that enhances its woodcutting ability.

A beaver's stomach is full of enzymes that enable the animal to digest woody material. This is particularly helpful once winter has set in and the beaver's only food source is the partially submerged food pile of branches adjacent to the lodge.

 

ADAPTION OF ENVIRONMENT: Beavers build dams and lodges by felling and limbing trees, and then dragging the cut materials to the building site. The logs and branches are packed together with mud and rocks to strengthen the structures. Lodges are constructed by piling logs and branches together in a dome shape. They then chew their way from under the water into the domed pile, creating an interior den. This den is lined with a mud pack that freezes solid in winter to insulate and protect the colony from predators approaching the lodge on the ice. The den is ventilated by air holes at the top and is accessible only from underwater passages (usually at least two).

Damming activities create wetland habitat for other species. When beavers dam a stream or river, water flows into adjoining areas and eventually

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Home sweet home! Beaver lodge built into lake bank with an underwater entrance. The den inside is dry and above water.

transforms that land. Woodland or meadow becomes a pond, creating suitable habitat for fish, wildfowl, reptiles and amphibians. These species in turn attract predators such as raptors, wading birds, otters, fishers and raccoons. Beavers are classified as a 'cornerstone species' due to their overall positive environmental impact.

The creation of wetland habitat from beavers building dams can cause hardship to landowners. Flooded roads and fields can adversely impact farming operations and flood homeowners' basements, as well as impacting day to day movement on surface roads. Some landowners resort to trapping and/or relocating beavers; however, suitable habitat will often attract new beavers.

One solution is to construct fences that sink into the ground and extend several feet around culvert mouths. The fence prevents the beavers from getting close enough to hear fast running water, which triggers their instinctive damming response. 'Beaver deceivers,’ or plastic pipes with small holes drilled in them, are placed through the dam walls to allow water to flow through at a very slow rate. A drop in water level around the lodge can expose the access tunnels, making the structure vulnerable to predators. It also makes it more dangerous for the animal to access food and building materials.

FAMILY LIFE: Beavers are very family-oriented with the adult females taking the dominant role. Once they reach three years of age they seek a mate. Pairs are monogamous and annually breed from January to March. The gestation period is 100-110 days. The babies, known as kits, are born from April to July. A female usually gives birth to 2-3 kits, each weighing about 1 lb. The kits are born fully furred and their teeth are erupted. They can swim and dive when 10 days old, and if necessary, can leave the lodge when they reach 30 days old. They drink their mother's milk for the first few months. After weaning it is on to leaves and plants. Yearlings help to gather food and building materials, and assist in repairing the dam and lodge, highlighting the cooperative nature of a beaver colony.

 

CREATURE WATCH: Beavers are predominantly nocturnal, so the best time of day to see them is from late afternoon, just before sunset, to sunrise. Chambers Lake at Hibernia County Park provides an opportunity to observe beavers if you are patient enough. The north end of Chambers Lake has one colony each on the east and west banks. The best way to see these colonies is from the water, so visitors with boats or kayaks have the best vantage point. Land-based observers can use binoculars or a spotting scope to bring the beavers into better focus. The best time of year to witness beaver activity is early spring through late fall.

Any time of year is a good time to marvel at the beaver's remarkable ability to use its unique adaptations to change its environment. This industrious and family focused rodent is a master builder and proficient environmental engineer whose labors create habitat for numerous other species. The beaver richly deserves the designation of 'cornerstone species'.