Beaver

The American Beavers are the second largest living rodent and the largest in North America. The adults weigh over 70 pounds and are 45 inches in length. They specialize in aquatics and have a nictitating membrane which covers their eyes while under water. They have valvular ears, nostrils and have webbed feet. The tails is broad, scaly and paddle like. Male are usually larger than females, the pelt has long, spinney guard hairs with a soft velvety under fur. Their color is usually chestnut with a rare blond mixed in. The ears are short, legs are short giving the body a more rotund look, and the forepaws are very dexterous. The toes of the hind feet are split to aid in combing fur. The geologic range of this family dates back to the Oligocene: some fossil forms reached the size of the modern day Black Bear. Beavers are best known for their industrious nature, the stability of the dams, large lodges (built from discarded branches that have been stripped of their bark which is the main food supply), and their extensive canal systems used to float their food home. Dening is done either in the family lodge or in mud dens built into the bank. They prefer Aspen trees, cottonwoods, and willows. Beavers can invade reservoirs, canals and irrigation ditches as long as they have a good food supply.

BEAVER BIOLOGY (CASTOR CANDESIS):

Beavers are best known for their industrious nature, the stability of the dams, large lodges (built from discarded branches that have been stripped of their bark which is the main food supply), and their extensive canal systems used to float their food home. Dening is done either in the family lodge or in mud dens built into the bank. They prefer Aspen trees, cottonwoods, and willows. Beavers can invade reservoirs, canals and irrigation ditches as long as they have a good food supply. The greatest damage done by beavers is the falling of trees and the loss of land to the ponds and lakes they form with the dams.

Food selection is very limited, they will eat a plant parts such as bark, buds, leaves, twigs of the quaking aspen, willows and cottonwoods. When these sources are low they will eat Alder river Birch, oak brush and conifer. Summer diet consists of aquatic (water) and terrestrial (land) herbaceous plants (plant that has leaves and stems that die down at the end of the growing season). They usually don’t range more than a few hundred meters in their search for food. Beavers intestines and stomach contain a microorganisms that to aid in the digestion of wood material. the beaver’s tail serves as an important fat-storage center. When a tree is felled it is the smaller upper branches that are used for food and the rest is used for maintenance of the dam and lodge.

BEAVER BEHAVIOR

The beaver is an excellent engineers, building dams, lodges, band burrows, and extensive canal systems; all of which is used to regulate the level of the water in the pond and float food and building materials back to the lodge. This “water management” is beneficial to the fish and the recovery of overgrazed and eroded stream banks. The materials are clutched to the chest with the forepaws or in the mouth. When construction occurs the wood is embedded in the stream bed, anchored by pilings and interlaced together with mud and rocks for increased strength. Some dams can be built as high as 2.5 meters and several hundred meters in width. The height of the dam is determined by the depth of water needed. The winter food source is stored below the freeze level. This source of storage is called a cache and starts off as a floating raft of food material. It then becomes water logged and sinks. The beavers then take the cut ends and embed it in the bank or floor of the stream or pond and the food is available all winter. This food cache looks from the bank as it a bush is growing out of the river bank under water.

The beaver is most active during dusk and night but have also been seen in broad daylight. The felling of trees almost always occurs during the dark of night. The lodges are built with water on three sides and the fourth side built on a steep river bank attached to the land. The Opening is under water and the living chamber is above water level. This chamber is 1.3 meter to 1.7 meter in size and as tall as 1 meter in height. The largest lodge ever recorded was 2 meter in height (above water level) and 12 meters in diameter. The temperature inside the living chamber is 1⁰ C and fluctuates that than 1⁰.

The beaver is a highly social, living in family units and extended family colonies. A colony consists of the adults, their yearlings and juvenile offspring and can range in number from 4 to 8 animals. General rule of thumb in the field is 1 lodge equals an average of 5 beavers. The whole family will defend the colony territory from other beavers. The adult female is the dominant member, she constructs the dam, food cache and warns the family with tail slaps to the water. The adult male inspects the dam, makes the territory boundary markings and usually is responsible for the felling and harvesting of the trees and gathering of the construction materials.

The young disperse from the colony at two years of age with the birth of a new litter. The young tend to move less than 16 km, depending on the food supply. Fighting over territory tends to be limited to the young who are trying to establish their own territory. The adult couple mates for life and mating occurs in January, February or as late as March. Gestation is 104 to 111 days and a litter of kits averages 3 however this number is determined by nutrition and elevation. Lower nutrition and higher altitudes lower the number if kits born per litter. The largest female on record weighed 69 pounds and contained 8 fetuses. Kits are born furred with eyes partially open. They grown rapidly are weaned at 6 weeks and the yearly female will mate in her 3rd year, earlier if nutrition is food.

Many believe the beaver to be the most fascinating wildlife to observe.

PREDATORS
Wolves, coyotes, bears, rover otters, lynx, bobcat, mountain lions and humans. There is a 30 % mortality rate average among the all classes.

DISEASES

Tularemia — is a disease of caused by the bacterium Francisella tularensis. Rabbits, hares, and rodents are especially susceptible and often die in large numbers during outbreaks. Humans can become infected through:

  • Tick and deer fly bites
  • contact with infected animals
  • drinking of contaminated water
  • Inhalation of contaminated dusts or aerosols

Beavers are also infested with parasites which can spread into your drinking or swimming water searching for hosts

Giardiasis — this disease found in beavers and other animals is a diarrhea illness caused by a one-celled, microscopic parasite that lives in the intestine of people and animals. It has become recognized as one of the most common causes of waterborne disease (drinking and recreational) in humans in the United States. The symptoms associated with giardiasis range from none (in light infections) to severe, chronic diarrhea. Giardia may be found in soil, food, water, or surfaces that have been contaminated. To protect yourself, practice good hygiene and avoid drinking or eating anything that may be contaminated. Boiling or filtering water removes the organisms that cause this disease.

Nematodes — are parasites that live on beavers and have been known to spread to humans. Nematodes in humans can cause a variety of problems, from lack of energy to blindness.

Trematodes — can also be passed to humans from beavers and can live in human intestines, liver and lungs, wreaking all sorts of havoc in these different organs.

Coccidians — are another beaver-human parasite that can cause fever, headache, muscle pain and swollen lymph glands.

NUISANCE CONCERNS
Humans are considered the biggest limiting factor to the population. Beavers manage watershed, slowing spring runoff, reducing floods and raining water tables. On the down side they fell costly landscaping, interfere with human engineering, plug culverts, block canals, flood rivers and enlarge ponds sometimes to the point of damaging surrounds houses, structures and roadways. Most states, Colorado included, have a trapping season for fur bearing due to the considerable economic impact. It is estimated beaver damage cost are as much as $23 million per year. The harvesting of the fur pelt in North American averages 1 million per year. It is estimated that 5 to 10 thousand animals are harvest each year.

REMOVAL
In 1996 Amendment 14 implemented a trapping ban in Colorado limiting all capture and removal to live methods. Conabears and other body catching lethal devices are illegal in Colorado. Although we always try to find a way to allow for co-existing, when removal is necessary the cages used are designed for live capture.

EXCLUSION AND RESTORATION
Vital tree protection and Water flow control devices can be installed. Our Wildlife Biologist and Conservationist is always available for consults. Based on his analysis we can devise a plan to regulate the water level, protect the trees, and perform population management if necessary.