BEAVERS

  

 Beavers in Wigry
 National Park
 Biology
 of beavers
 History
 of beavers
 in Poland
 Beaver's impact
 on environment
 WNP homepage

  

Text:
Wojciech
Misiukiewicz

Photos:
Wojciech Misiukiewicz
Maciej
Kamiñski

Drawing
Anna Szkiruĉ

Webdesign: 
KAJA
 
2003

  

  

  

Biology of beavers

  

Beaver is a slow
yet a very persistent swimmer.

The European beaver Castor fiber is the largest European representative of rodents (Rodentia). It leads an amphibian mode of life and is perfectly adapted for residing in water. Its spindle-shaped trunk facilitates swimming. The streamlined body, and particularly the location of nostrils, eyes and ears - almost in-line, high on the skull - prove the animal's adaptation to the existence in aquatic environment. Its thick hair, with abundant, fluffy bottom layer serves as protection from cold and moisture. Beavers are usually black although sometimes the fur colour is brown.

  

  

  

  

European beaver (Castor fiber)

The beaver is a strong, stocky animal with a flattened head and a wide, flattened tail covered with scaly skin. Such tail is unique among mammals. It is 20-25 cm. long and 11-18 cm. wide. When a beaver is in the water, it uses it as a rudder and an additional driving force, whereas on the ground it serves the purpose of a support, when the animal has to raise on its rear paws to cut down a tree or carry twigs. It also serves the purpose of an organ regulating the animal's body temperature. In hunting dialect, the tail is called a "plusk" or "kielnia", because in case of emergency the animal uses it to hit the water surface in order to warn the other colony members about the presence of an enemy.

The beaver uses its front paws with great dexterity for digging canals and dens, cleaning its fur, playing, or even eating the leaves that are too large to fit into its snout. The front paws are short, fine and prehensile and the toes of back paws are attached to each other by a bald skin fold. Although the beaver uses its tail when swimming in the water, the main driving force are the back paws.

  

Beaver spends much time grooming.

Beavers swim relatively slow, but persistently. They are great divers and can remain underwater for as long as 10 minutes or even longer. While diving, the nostrils, ears, and also the anus, close. The animal is equipped with a third eye-lid that provides good underwater vision while also protecting the eyes. The mouth opening is closed by hairy lips, right behind the incisors. Thanks to the special positioning of the back part of the tongue, the animal can close the throat outlet to oral cavity, and at the same time breathe normally through its nose, with the snout open. Such skill is needed for erecting dams, building lodges and gathering food provisions.

  

The incisors are beaver's most powerful tool. The upper ones are 10-12 cm. long, and covered with brown-red glaze. Two upper incisors are used as levers for the low incisors, which provides beavers with solid support when cutting down the hardest species of trees. The beaver has 20 teeth. Hearing, smell and touch are beaver's best developed senses. The vision is retarded.

  

  

Beavers copulating in the water.

Beavers are monogamous animals that live in families. They are sexually mature at the age of 3-4 years, the mating season falls in the second half of January. The courtship take place in the water. After many chases, the animals copulate facing each other, usually in the water, and sometimes also under the ice. During the mating season, the animals are loud as they often squeal. Sometimes they copulate during the day. Baby beavers, usually three of them, are born 100-110 days later. A baby beaver can swim almost right after its birth. However, it can dive only at the beginning of the second or third week of its life.

  

Marking the area with scent.
All family members mark their area using beaver scent

The parents, as well as juvenile beavers from the previous litter, take care of baby beavers and accompany them during their first trips outside the lodge or den. During those trips outside their home nest, baby beavers dive into the underwater in the presence of one of the older family members. They will remain in the family nest for 2 years before they take off in the third spring of their life in order to set up their own families. Upon reaching sexual maturity, young beavers usually travel over 10 kilometres before they set up a new home. If everything goes well, a beaver can reach the age of 15-20 years - older individuals are rare.

  

Beaver is an amphibian animal that resides within the neighbourhood of water bodies and watercourses. Each family protects its area and food resources. Every family member marks the area using the secretion from the glands located near the anus. The animals use mud, decaying plants and twigs to build small mounds that are later marked with the secretion recognised by all family members. The scent provides the "owners" of the area, their neighbours and travelling individuals with information that the area is already inhabited, and that any approaching individual should turn back from its way.

  

From late autumn till early spring
beavers intensively cut down trees
and bushes.

The presence of beavers can be determined by bite marks on trees and bushes as well as by the dug canals that the animals use to transport the branches to their nest. The beaver adapts its nest to the surrounding environment. On the river shores, if the terrain configuration allows it, the beavers do not build lodges but dig dens with underwater entrances. The structure of dens is complex with the total length possibly exceeding 50 m, and sometimes reaching as much as 100 m. The den system can be multilevel and consist of several nesting dens. In areas where the low river shores make it impossible to dig dens, beavers build lodges. They are usually situated on the shores overgrown by trees, where the water is deep and calm. The construction material are branches sealed with mud, forming a mound that may be as high as 3.5 m. high. There is usually one living chamber in a beaver's lodge, where baby beavers are born and raised. The entrance is always located underwater. The whole nest seems to be two-levelled. The floor of the lodge's vestibule is located at the height of the water surface and is a place where a beaver can dry itself. The second level is lined with dry wood chips, plants and twigs that the animals use as a bedding. The beavers keep their nest clean and regularly provide it with fresh wood chips and twigs. The lodge is constantly enlarged and rebuilt, especially in the late autumn, when the beavers prepare for winter.

  

The beaver's diet is dominated by aquatic and near-shore plant species. Beavers feed on them regularly during the whole year, except for the winter, when they mainly feed on tree and bush twigs stored near the lodge. During the summer their diet is definitely more diversified. As a herbivorous animal, the beaver includes various species of aquatic and herbaceous vegetation in its diet, such as Nymphaea, Nuphar, pondweeds and duckweeds. Between late autumn and early spring their diet is mainly composed of bark, pulp, sprouts and leaves of trees and bushes among which willow, aspen, birch and hazel are the most eagerly eaten. A single individual is capable of striking down a 30 cm. wide aspen tree in 15 minutes. The cut down trees, stubs and beaver's feeding spots can be found on the shores of almost every water body in Wigierski National Park.

  

  

  

 

  

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