Beaver Poland Karol Zub

Eurasian beaver - Castor fiber

Family:
Beaver (Castoridae)
Status:
Least Concern

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Taxonomic status

Scientific name

Castor fiber

Common name

Eurasian beaver

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Species information

Physical characteristics

Body Length 70-100 cm
Tail Length 25-37 cm
Tail wide 12-16,5 cm
Weight 15-35 kg


The Beaver is the largest rodent in Europe. It has grey to dark-brown fur, although the fur colour of European beavers varies geographically. Light, chestnut-rust is the dominant colour in Belarus. In Russia, the beavers of the Sozh River basin are predominantly blackish brown, while beavers in the Voronezh Reserve are approximately equally divided between the brown and the blackish-brown variety.

Eurasian beavers have two castoreum glands located next to the cloacal opening. These glands produce a pungent, sweet smelling chemical called castoreum, which is used to mark territories.

The muzzle is blunt, the ears are small, and the legs are short. Both the ears and nostrils are valvular and the eyes have nictitating membranes, which close when the animals swim under water. The tail is broad, oval, flattened horizontally, covered in scales and black. The feet are dark brown to black and have 5 digits each. The rear feet are webbed and the two middle  toes have a split nail used for grooming. The tail is narrower and the skull smaller than that of the North American beaver, Castor canadensis.

Inside the mouth, beavers have a skin fold that allows them to gnaw on branches under water without getting water in their mouths. They have two large incisor teeth with hard, orange-colored enamel on the anterior surface.

There is sexes appear much alike, although females tend to be slightly larger.

A beaver eating fresh twigs from mainly willow

A beaver eating fresh twigs from mainly willow

Different from the American Beaver

Although superficially similar to the North American beaver, there are several important differences.
European beavers tend to be:

  • bigger
  • with larger, less rounded heads
  • longer, narrower muzzles
  • thinner, shorter, and lighter underfur
  • narrower, less oval-shaped tails
  • have shorter shin bones, making them less capable of bipedal locomotion than the North American species
  • European beavers have longer nasal bones than their American cousins, with the widest point being at the end of the snout for the former, and in the middle for the latter
  • The nasal opening for the European species is triangular, unlike that of the North American race which is square.

Genetics

The two species are not genetically compatible. North American beavers have 40 chromosomes, while European beavers have 48. Over 27 attempts were made in Russia to hybridize the two species, with one breeding between a male North American beaver and a female European resulting in one stillborn kit. Therefore, inter-specific breeding is unlikely in areas where the two species' ranges overlap.

Habitat, behaviour, food and reproduction

Habitat

Beavers are adapted to a semi-aquatic life, using a variety of freshwater systems, including rivers, streams, irrigation ditches, lakes, and swamps.

They generally prefer freshwater habitats surrounded by woodland, but may occur in agricultural land or even suburban and urban areas. In northern Scandinavia, beavers may be found right up to the limit of the willow zone in the mountains, where knee-high willow bushes are the only woody vegetation and the terrain is frozen for 8 months of the year. While it is not their preferred habitat, beavers have been known to survive there.

In many places, beavers inhabit both the valley floor and the surrounding wooded mountain plateaus, with a gap in distribution where streams flow down steep valley sides. In general, beavers should be able to live in almost any freshwater habitat where there are trees or shrubs and the gradient is not precipitous. However, patterns of recolonisation demonstrate a clear preference for still or slow laminar water flow if it is available.

Eurasian beaver home range size varies by available food, watershed size, colony size, and time of year. During the winter months territory size drops to an area that can be patrolled daily with one trip under water, due to the ice cover. During the warm season, territory size can extend from 1 to 5 kilometers along a shoreline.

Behaviour

Eurasian beavers are primarily nocturnal, although they may also be active during the day. Their dens are usually burrows in the bank of a river or pond. In locations where the bank is not suitable, they construct lodges away from shore out of sticks and mud. In the lodges, beavers live in colonies of up to 12. These colonies consist of only one dominant, monogamous breeding pair. The dominant female decides when it is time for the young to travel outside the den and when the young need to disperse.

Beavers are semi-aquatic and can stay under water for 4 to 5 minutes at a time. They are active throughout the year, hardly ever venturing above the ice surface during the winter months in their northernmost regions. For this reason beavers spend the autumn season building food caches in the water to last them through the winter. These food caches consist of woody vegetation, such as willow and aspen branches.

Beavers are a keystone species, due to their ability to change the flow and nutrient cycling of a watershed by building dams to regulate water depth. However, Eurasian beavers are more conservative than their North American cousins, usually constructing much smaller dams and lodges. Eurasian beavers are very territorial and mark their territory with castoreum, a form of olfactory communication. They do this by building a scent mound on the shore. They bring mud and vegetation up from the bottom, holding it tight to their chest with their forelegs and pushing themselves up the bank with their hind legs until they have a mound. The beaver will then apply castoreum to the mud pile creating a scent mound. Beavers act very aggressively towards an unknown scent mound in their territory, often hissing at it and slapping the water with the tail and resurfacing right away. Most often they will create a scent mound next to it or on top of it.

Eurasian beavers must groom themselves constantly to maintain the water repellency of their fur. They use the split toe nails on their rear toes to comb oils from their oil glands into their guard hairs. This makes the outer layer of fur waterproof and the inner layer never gets wet. Without these oils, beavers would become wet to the skin and not be able to spend as much time in the water or withstand cold water temperatures.

Beaver dam with in the back the lodge

Food

Eurasian beavers are herbivores, feeding primarily on woody vegetation in the winter months. They prefer willow, aspen, and birch trees with diameters less than 10 cm. These food items are stored in the water during the fall months in large quantities. These food caches need to be large enough to last the entire colony until the ice melts in the spring of the year.

Beaver activity in the Millingerwaard, the Netherlands

During summer months beavers feed heavily on aquatic vegetation, shoots, twigs, bark, leaves, buds, and roots. In agricultural areas beavers will consume crops as well. They prefer herbaceous plant foods over woody vegetation when it is available.

Beavers do not produce cellulases, an enzyme used to break down cellulose. However, they are coprophagous, taking up faecal microbes during reingestion which help break down cellulose that can be absorbed after reingestion.

Reproduction

Eurasian beavers are monogamous and only one adult pair breeds per colony. Females come into estrus between January and February, but sometimes warm winter weather can result in a breeding season as early as December.

Young beaver

Copulation takes place in the water most of the time but, in some cases, it takes place in the lodge. The male will approach a female floating in the water from the side, and intercourse may last anywhere from 30 seconds to 3 minutes. Most copulations occur at night. If a mature female is not impregnated the first time she will come into estrus 2 to 4 times again throughout the season.

Family members cooperate to care for the young of the primary pair.

Eurasian beavers breed yearly in the spring between January and February. The gestation period is 60 to 128 days and they can have up to 6 or more young, but 1 to 3 is more common. Newborn weight is 230 to 630 grams and the young are usually weaned by 6 weeks old. During that time the female takes care of the young, cleaning and feeding them. After the young are weaned, sub-adults in the colony help feed them by bringing small twigs and soft bark to them until they are about 3 months old. At 1,5 to 2 years old young beavers disperse, often being forced out by the adult female. After dispersal they become sub-adults at another colony until they are ready to breed and start their own colony.

Gestation Period 60-128 days
Young per Birth 6 or more
Weaning 6 weeks
Sexual Maturity about 1,5 years
Life Span 7 to 8 years


Eurasian beavers live in small family groups consisting of one breeding adult female and male, young of the year, yearlings, and sub-adults. The young are skittish outside the lodge and are never far from an adult.

Eurasian beavers can live 10 to 17 years long, but rarely live longer than 7 to 8 years in the wild. In captivity, some sources suggest that beavers can live up to 35 years and are expected to reach 24 years of age. However, these ages are unconfirmed. A confirmed record of longevity in captivity in Castor fiber was 13,7 years old.

Communication

Eurasian beavers communicate mainly through chemical communication. Not only do they use castoreum to mark territory, but they also use their oil glands to distinguish between males and females. Eurasian beavers also use postures, tail slapping, and vocalizations. Vocalizations include whining calls, whistling, and hissing. Tail slapping is used when they are frightened or upset.

Landscape shapers

Eurasian beavers have the ability to impact ecosystems tremendously. Through the process of building dams they alter the flow of the water and flood many acres of former uplands. Dams build up sediments and debris which increase carbon and decrease available nitrogen and acidity. This changes the invertebrate community from running water invertebrates to still water invertebrates.

The new water source attracts new species of birds, fish, and amphibians by providing a suitable water table. Eurasian beavers also maintain certain woody vegetation in the sapling stages for extended periods of time through their browsing activities.

Flooded timber will die off in a year and soon a once forested ecosystem becomes an open water ecosystem. Eurasian beavers can also alter, in time, the stand structure around the waters edge. They do this through their food selection, making conditions favorable for unselected food items.

Eurasian beavers start with a small stream and build a dam, flooding a forested area. Once the beavers use up available resources, they move on and abandon the pond. Succession in the pond leads to the development of marsh habitat and then meadow. The decrease in nitrogen and acidity along with the increase in carbon hinders the growth of woody vegetation for some time but eventually woody vegetation begins to grow forest is regenerated.

Predation

A difficult catch

Lodges and burrows in the bank make beavers mostly inaccessible to predators.

By far the most successful predators of Eurasian beavers are humans. Eurasian beavers were almost hunted and trapped to extinction for their prized pelts and castoreum. Today, with conservation efforts in place, Eurasian beavers are protected by law. Poaching, entanglement in nets, and road accidents are the leading causes of death.

Natural predators are Wolves, Brown bear, and Red foxes.

The leading cause of death in Castor fiber today is infectious disease.

Alarm call

Eurasian beavers use a “tail slap” when they are frightened, which is a warning to all other beavers that something is near. Beavers slap the water surface with the tail as they dive under water and out of harms way. In response, all beavers in the area will do the same. They will also avoid food items that have the odors of predators on them.

Population size and trends

World

By the beginning of the 20th century, the global population had been reduced to eight populations, totalling approximately 1,200 individuals. Protection (beginning with a hunting ban implemented in Norway in 1845), natural spread and reintroductions have resulted in a rapid recovery in numbers and range, particularly in Europe.

In 1998, the global population was estimated at 430,000, by 2002 it had reached at least 593,000, and in 2006 the minimum estimate was 639,000. This is almost certainly a considerable underestimate, as both population and range are in rapid expansion. Considerable further expansion in range and population, especially in western Europe and the lower Danube basin, can be expected. If current trends continue, the Eurasian beaver will be a fairly common mammal in much of Europe within the next few decades.

Asia

However, populations in Asia are still considered small. In Mongolia, reintroductions have been successful and the population has reached 150, and in China the population is about 700.

In Mongolia in 1964, the population size was estimated to consist of 100-150 individuals, rising to 200 individuals by 1973. In 1991, surveys estimated there to be approximately 300 individuals along Bulgan and Hovd rivers. The most recent population assessment was conducted in 2004, which recorded 40 lodges along Hovd River and estimated the population to consist of 130-150 individuals. Ten beaver settlements were recorded in the Tuvan section of Tes River in 2005, and the Mongolian section of this river is believed to contain a similar beaver population.

The Chinese subspecies of the Eurasian Beaver (Castor fiber birulai) is one of the rarest and least known aquatic mammals in China. In the 1970's it was believed that only 100 animals remained in fewer than 20 family groups. Currently, only one substantial population is known, at the Buergan River Beaver Reserve along the Xinjiang-Mongolian border - a narrow strip 50 km long and only 500 m wide. Here the population is estimated to be only 500 animals, and only 700 may live in all of China.

AreaNumbersDevelopment
World639,000Increasing
China700Increasing
Mongolia150Increasing
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Distribution: maps, historical and current

Countries

Landscapes

Interactive map

Castor fiber – Eurasian beaver: current distribution
Source: IUCN Red List of Threatened Species


View Eurasian Beaver - current distribution in a larger map

Further map information

Range map Eurasian beaver

Historical distribution

This species was once widespread throughout Eurasia.

Current distribution

Europe and Asia

The Eurasian beaver Castor fiber was once widespread in Europe and Asia. However, by the beginning of the 20th century, over-hunting had drastically reduced both the numbers and range of the species. In Europe, only a few isolated sites remained: parts of the Rhone (France) and Elbe (Germany), southern Norway, the Neman River and Dnepr Basin (Belarus) and Voronezh (Russia). A series of management measures and reintroductions have enabled the beaver to return to much of its former range, and there are now a number of rapidly expanding populations extending from Spain and France across central and eastern Europe to European Russia, Scandinavia and parts of western Finland.

  • The Eurasian beaver is native in: Belarus; China; France; Germany; Kazakhstan; Luxembourg; Mongolia; Norway; Russian Federation.
  • It is regionally extinct in Moldova; Portugal; Turkey; United Kingdom.
  • Castor fiber was reintroduced in: Austria; Belgium; Croatia; Czech Republic; Denmark; Estonia; Finland; Hungary; Italy; Latvia; Liechtenstein; Lithuania; Montenegro; Netherlands; Poland; Romania; Serbia; Slovakia; Slovenia; Spain; Sweden; Switzerland; Ukraine.
  • Its origin is still uncertain in Bulgaria.

Europe

Free-living populations of beavers are now established or establishing in most regions of their former European range, the main exceptions to date being Portugal, Italy, the south Balkans and Great Britain. Detailed information on the status and distribution of the Eurasian beaver in each range state can be found in Halley and Rosell (2002), and information on the population that was translocated to Spain in 2003 can be found in Ceña et al. (2004). It is generally a lowland species, but occurs at altitudes of up to 850 metres a.s.l. in Europe.

 

Beaver swimming

Mongolia

In Mongolia, a small population exists along the Bulgan River in northern Dzungarian Gobi Desert, in the south-western corner of Mongolia. Mongolian-German Biological Expeditions carried out conservation introductions along Hovd River in Mongol Altai Mountain Range in 1974, 1975, and 1978, and along Tes River in northern Hangai Mountain Range in 1985, 1988 and 2002. In all cases Mongolian beavers from the Bulgan River were used in order to protect the gene pool in the central Asiatic hydro-geographic basin. A separate attempt to reintroduce beavers from Voronezh Reserve (Russian Federation) was unsuccessful.

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Threats

Overhunting, meat and castoreum

The beaver's historic decline was caused by over-hunting for fur, meat and castoreum (a secretion from the scent glands), combined with loss of wetland habitats. Beaver populations were severely reduced in most countries by mediæval times, but the species clung on in marshes and other inaccessible places until the advent of efficient steel traps and accurate firearms in the 17th century. Throughout the 19th century this resulted in many populations going extinct for, combined with drainage of many of the large marshland areas in which the species clung on (all of the European refugia where the species survived, except in Norway, are extensive marshlands).

Today, beaver populations in Europe are expanding rapidly, and there are no major threats (i.e. threats of a magnitude likely to cause decline at the regional level). Competitive exclusion of the native European beaver Castor fiber by its American cousin Castor canadensis may be a threat in parts of Finland and North-west Russia, but it is not a major threat regionally. In Europe, North American beavers are now confined entirely to Finland and north-west Russia, where populations are increasing only slowly (due to heavy harvesting).

The former population at a reservoir near Paris has been removed, and populations introduced to Poland and Austria have apparently gone extinct in competition with Castor fiber, as opposed to what has tended to happen in Finland and North-west Russia. It has been suggested that due to differences in the life history of the two species, Eurasian beavers may have a competitive advantage at more southerly latitudes, whilst North American beavers may be more successful further North. There are no serious prospects of further introductions. The two species do not interbreed.

Road kill

Road kill is an important source of mortality for some populations. Rapidly expanding beaver populations may also come into conflict with humans in some areas, as they do some damage to forestry and crops. Such damages should be put into perspective: they tend to be less severe than those caused by other species such as deer and voles, but are noticed because beavers are a new and unfamiliar species in areas where they have been recently introduced.

Illegal hunting

In Mongolia, illegal hunting for skins, meat and castoreum still occurs in some areas such as the Tes River.

Habitat loss and water pollution

Habitat loss through selective clear-cutting of willow, upon which this species relies for food and shelter is also a threat; this is known to be occurring along the Bulgan River and is leading to isolation of small populations and inbreeding. Pollution of water systems is also a threat. A hydroelectric dam in the Chinese section of the Bulgan River prevents migrations in this area.

Loss of food resources

In China, firewood gathering has depleted much of the forest on which the beavers need to subsist, and heavy grazing pressure has further reduced vegetation needed by beavers.

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Conservation information

IUCN Red List

Least Concern:

EU habitat directive

Annex V for the Swedish and Finnish populations, Annex II and IV for all others

CITES

-

EU Wildlife trade regulation EC Reg. 338/97

-

Bern convention

Appendix III

Bonn convention

-

Conservation status

The Eurasian beaver has shown good recovery across much of its range, as a result of conservation programmes. The highest numbers are found within Europe. Conservation measures are ongoing to prevent the population declining again and as long as these continue, there is no reason to continue to assess the species as Threatened or Near Threatened. Now it is listed by the IUCN as Least Concern. However, the Asian populations remain very small and under serious threat, and these populations urgently need conservation measures.

Conservation measures

A number of conservation measures have contributed to the species' recovery in Europe, including reintroductions and translocations, hunting restrictions, and habitat protection. In Finland, Castor canadensis populations are controlled to prevent them spreading into the West where Castor fiber occurs.

Regulated hunting

Regulated hunting is recommended as the optimal management regime in managed landscapes with healthy beaver populations. Management of beaver populations should be implemented at the watershed scale, except where large human-made dams form significant barriers to spread.

Early provision of interpretation and public viewing opportunities is also recommended, as this provides a benefit to the local economy through wildlife tourism, and helps foster positive attitudes to beavers. This has been a successful feature of several recent reintroductions. Reintroduction to Italy has been recommended in a European Union/Bern Convention Nature and Environment Series document. Considerable efforts have been made to develop a beaver reintroduction programme in Scotland, and a full public consultation showed strong support for such a scheme among the general public, including in rural areas where beavers were likely to be released.

Castor fiber birulai

In Mongolia, Castor fiber birulai is protected as Very Rare under part 7.1 of the Law of the Mongolian Animal Kingdom (2000), and is included as Rare in both the 1987 and 1997 Mongolian Red Books. This subspecies is also listed as Very Rare under the 1995 Mongolian Hunting Law. Approximately 11% of the species’ range in Mongolia occurs within protected areas.

Conservation measures in place in Mongolia:

1) Bulgan Gol Nature Reserve was established along the Bulgan River in 1965 to conserve this species.
2) Many translocations and conservation introductions have taken place over the past 50 years to enhance the Mongolian population.

The species is considered Endangered (EN A1bcd) in the Chinese Red List.

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Photos and other pictures to add

Twee bevers

Eurasian beavers
Pair of Eurasian beavers swimming in nature area the Millingerwaard, Netherlands
Source: M. Kaandorp & C. Lange
Rights: May be used by LHNet

Additional photos

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Experts and scientific referees

IUCN SSC

For more detailed information view the 'Eurasian beaver - Castor fiber' page on to the IUCN Red List of threatened species.

Kaandorp, Manon

Wildlife Management; GIS; expertise on large mammals; coordinating research projects
Project Officer at ECNC-European Centre for Nature Conservation

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Sources

Wikipedia

Holden, J. and C. Yahnke

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