Tuesday, 25 December 2012

Week 3: Eurasian Beaver (Castor Fiber)

The Eurasian Beaver was @SpeciesofUK from 16th to 22nd December 2012.

There are two species of beavers: the North American Beaver and the Eurasian Beaver. Eurasian beavers are sightly the larger of the two species, and have narrower muzzles and tails.  North American Beavers tend to build larger dams on bigger rivers.

By 1900, Eurasian beavers had been hunted near to extinction, with just 1,200 individuals left. Now, they are widespread from the UK to China and Mongolia.1

The Eurasian beaver is the world's second largest rodent after the capybara. Unusually for mammals, female beavers are (slightly) larger than males.2

Eurasian Beaver
[Source: Per Harald Olsen]

Beavers live in freshwater lakes and slow-moving rivers. They're crepuscular (active dawn and dusk) and don't hibernate. In summer they mostly eat vegetation like grasses; in winter tree bark, leaves and twigs.3

Beavers are highly territorial, live in family groups, and are thought to be monogamous. They mate in Jan-Feb. Two to four kits (baby beavers) are born in spring. They stay with parents until 2 yrs old then find their own territory.4

Beavers in the UK

Eurasian Beavers are native to the UK but were wiped out sometime around the 12th - 16th centuries by hunting.

Recently, however, two new wild beaver populations have been introduced to the UK, both of them in Scotland.  The first population is centred in Tayside and has recently been estimated to number 146 individuals.5 They orginated from escaped captive beavers, and for a time the Scottish Government had asked for them to be rounded up.  The second is the official Scottish Beaver Trial in Knapdale, Argyll & Bute. This is a five year project that began in 2009. The aim of the trial is to explore how beavers can enhance the local environment and to assess any impact they have.6 The results will inform the future of beavers in Scotland.

Beaver and Kit
[Source: Ray Scott]

Beaver Adaptations

Beavers, as semi-aquatic mammals, have developed an amazing array of adaptations to their environment.

The ears, eyes and nose of a beaver are high up on its head so it can remain observant & inconspicuous while swimming.  They have dense underfur & long (60-65 mm) stiff dark guard hairs that help trap air for warmth and repel water.7 Beavers can remain underwater for up to 15 minutes at a time. In winter they will even swim under the ice!

Beaver teeth have a hard enamel layer (coloured orange) at the the front and a softer dentine at the back. As they gnaw, this naturally creates a chisel-like shape. Here is a video of beaver teeth in action!  Beavers eat birch, oak, rowan, alder and willow, and they are especially partial to aspen and poplar.8

Beavers sometimes store food under the water near the entrance of their lodge. That stops it getting frozen in the winter. They have a special tissue that seals their mouth behind their teeth so they can gnaw at bark even while under water.

The tail has to be the beaver's most incredible adaptation. It is flat and scaly. It is used to steer through the water and for balancing the weight of heavy logs.10 The fat in the tail helps the beaver to thermo-regulate. Most famously of all, beavers use their tails as an alarm signal, slapping it loudly on the water and then diving underneath!

Beavers' Tails
[Source: Groucho M]

Nature's Engineers

Beavers feel safe surrounded by water, so they sometimes build dams to create deeper ponds for their lodges. Beaver dams alter water flow however they can create biodiversity hotspots by introducing new wetland microsystems.

Beaver Dam
[Source: Juliux]

Beavers build lodges when the banks of the river are not large enough for them to build a burrow the size they would like. The living chamber of a burrow is above water, but the entrance is under water. Dams help submerge the entrance.

As well as dams and lodges, beavers even construct canals so they can travel further and float materials along for building and food.11

Beavers stimulate new tree growth by gnawing on tree stems and, effectively, coppicing. There's a strong argument that by felling established trees and stimulating new tree growth, beavers keep woodland areas renewing.

Beavers in Culture

'Beaver' comes from Old English 'beofor.' Similar Germanic roots are evident in Old Norse 'biōrr' and Old High German 'bibar.'12 Beaver was originally slang for 'a bearded man,' but by 1927 was being used as vulgar slang for female genitals.13

In the twelth century, Gerald of Wales wrote a passage on the beaver. This includes a famous quote that is sometimes used to illustrate how rare beavers had become in the UK: “Teivi is...the only river in Wales, or even in England, which has beavers; in Scotland they're...found in one river.”

Lewis Carroll included a beaver in his famous nonsense poem 'The Hunting of the Snark':

          There was also a Beaver, that paced on the deck,
          Or would sit making lace in the bow
          And had often (the Bellman said) saved them from wreck,
          Though none of the sailors knew how.

The most famous beavers in literature are Mr and Mrs Beaver from The Lion, The Witch & The Wardrobe by C S Lewis. The Beavers in Narnia are examplars of people with absolute faith in Aslan's prophecies.14

Beavers are such a unique animal they have become iconic for some countries and institutions. Canada adopted the beaver as its national symbol in 1975. The oldest corporation in America the Hudson's Bay Co. has had beavers on its crest since 1678. Even the London School of Economics has a beaver emblem! It was selected for its "foresight, constructiveness and industrious behaviour"

Beaver Products

Beavers were hunted close to extinction because they were used for a number of products.

They were hunted first and foremost for their meat and fur. The fur was valued for its inner soft layer. This was used for 'beaver' hats or coats like this worn by Oscar Wilde:

Oscar Wilde in Beaver Coat
[Source: Library of Congress]

Beaver teeth were used by the Anglo-Saxons to make pendants, such as this one at the British Museum or this in Sheffield.

Beaver testicles have been used in some cultures for traditional medicine.15

Beavers produce a secretion called castoreum. Once this was used to treat ailments such as aches and pains. Even now, it is used in perfume and as food additive.16 Salicylic acid, which is present in castoreum, remains an ingredient of aspirin drugs today!

Strange but True...

Remains of a now extinct giant beaver have been excavated, including one in the UK. At the time of writing, one of its teeth was actually up for sale, here!


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