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R. Campbell-Palmer, D. Gow, R. Campbell, H. Dickinson, S. Girling, J. Gurnell, D. Halley, S. Jones, S. Lisle, H. Parker, G. Schwab and F. Rosell

This book should be cited as Campbell-Palmer, R. et al. (2016) The Eurasian Beaver Handbook: Ecology and Management of Castor fiber. Exeter: Pelagic Publishing, UK.

All rights reserved. No part of this document may be produced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise without prior permission from the publisher. While every effort has been made in the preparation of this book to ensure the accuracy of the information presented, the information contained in this book is sold without warranty, either express or implied. Neither the authors, nor Pelagic Publishing, its agents and distributors will be held liable for any damage or loss caused or alleged to be caused directly or indirectly by this book.

Cover images: beaver, Graham Brown; landscape, Roisin Campbell-Palmer; culvert protection, Skip Lisle; piped dam, Gerhard Schwab.

Primarily funded by Colchester Zoo, the Welsh Wildlife Trust and the Wildlife Trust, with additional contributions from the Royal Zoological Society of Scotland, Bund Naturschutz, Telemark University College and Scottish Wildlife Trust.

Róisín Campbell-Palmer, Field Operations Manager, Scottish Beaver Trial, and Conservation Projects Manager, Royal Zoological Society of Scotland, UK. PhD candidate, Telemark University College, Norway.

Dr Ruairidh Campbell, Wildlife Conservation Research Unit, Department of Zoology, University of Oxford, UK.

Helen Dickinson, Tayside Beaver Project Officer, Scottish Wildlife Trust, UK.

Dr Simon Girling, MRCVS, Head of Veterinary Services, Royal Zoological Society of Scotland, UK.

Derek Gow, Director, Derek Gow Consultancy Ltd, Upcott Grange Farm, Lifton, Devon, UK.

Simon Jones, Project Manager, Scottish Beaver Trial, and Director of Conservation, Scottish Wildlife Trust, UK.

I remember my first real contact with beavers in the wild, 35 years ago, when I was staying on a farm in Jamtland in Sweden. My host, Erik, was a hunter and a farmer who also worked in the local town; his family farm was in beautiful countryside with ospreys, goldeneye ducks and cranes breeding in the bogs; in the forests lived elk and beavers. I remember thinking it was as Scotland should be. One evening, I walked to the sluggish river which ran nearby – and, after a mosquito-tormented stalk, I saw my first beaver. It sensed me, though, and with a slap of its tail it was gone. I sat down on a jumble of beaver-felled birch trees, but my wait was in vain. I asked Erik what he thought about the birch trees felled by the beavers across his track. His reply was so sensible: ‘I wait until winter and then drive down with my tractor and trailer and log up those trees – they are nicely seasoned and ready for my log store. And sometimes I hunt one; would you like beaver for supper tomorrow? I’ll get some out of the deep freeze.’ I thought it tasted good, nicely braised – something between brown hare and roe.

I liked the matter-of-fact way in which he lived with the beavers but he also recognised their value in the wetland ecosystem. That value is what this excellent book is about; it’s written by 12 experts who have brought together a wealth of experience and, most importantly, a mine of information on how we can learn to live with beavers again in the United Kingdom.

I’m so pleased that beavers are back in our country, because I recognise they are essential in helping to manage natural wetland ecosystems. It’s been a long time coming, and much longer than I expected when I was part of the first serious discussions as a main board member of Scottish Natural Heritage back in the early 1990s. A successful scientific trial has been carried out by the Royal Zoological Society of Scotland and Scottish Wildlife Trust on land owned by Forestry Commission Scotland, and with scientific input from Scottish Natural Heritage. Beavers, being beavers, have also cropped up on their own in the Tay catchment of Scotland and occasionally elsewhere in Britain. The Scottish Government will soon, I hope, make the decision that this important keystone species should once again be part of our natural fauna, and we can see them restored to their original haunts.

During my wanderings looking at beavers and talking with beaver experts in a variety of European countries, I have been impressed by their knowledge and their understanding of the species within their home countries. They take a common-sense approach of working and living with an animal that can spring a few surprises.

In the pages that follow, the reader can get everything they need to know about the history and ecology of beavers, their impacts on human operations and their value within the ecosystem. This restoring of functioning ecosystems in such a fragile world will be more and more at the centre of our nature-conservation ethos. The authors write on many aspects of how to manage beavers and our activities; from proactive dam management to novel methods of reducing their impact on our interests. There is information on trapping, translocation, culling and many other subjects. It’s always been my view that, to have beavers back throughout Britain, we will need robust management and a rapid response to those who ask for help to act against beavers that cause problems.

The main part of this handbook finishes with learning to live with beavers – and that could be the most important aspect. I believe that it’s crucial for farmer, fisher, forester or any of us to learn to accept that although some species may at times cause us problems, we should remember the myriad species and actions of the natural world that allow us to farm and fish, to grow crops and trees, and to have fresh water and breathe fresh air. We, like the beavers, are part of the great ecosystem we call the Earth. Let us celebrate the return of the water engineer supreme.

Rydw i’n cofio fy nghyswllt cyntaf erioed gydag afancod yn y gwyllt, 35 mlynedd yn ôl pan oeddwn i’n aros ar fferm yn Jamtland yn Sweden. Roeddwn i’n aros gydag Erik, heliwr a ffermwr a oedd hefyd yn gweithio yn y dref leol. Roedd ei fferm deuluol yng nghanol cefn gwlad bendigedig gyda gweilch y pysgod, hwyaid llygaid aur a garanod yn magu ar y corsydd ac, yn y coedwigoedd, roedd elcod ac afancod yn byw. Rydw i’n cofio meddwl mai fel hyn y dylai’r Alban fod. Un noson, fe gerddais i at yr afon a oedd yn llifo’n araf heibio ac, ar ôl cael fy erlid gan fosgito, fe welais i fy afanc cyntaf; ond roedd wedi synhwyro fy mod i’n nesáu ac ar drawiad ei gynffon, roedd wedi diflannu. Fe eisteddais i i lawr ar bentwr o goed bedw wedi’u torri gan yr afanc, ond offer fu’r aros. Holais Erik am ei farn am y coed bedw wedi’u torri gan yr afancod ar draws ei lwybr. Roedd ei ymateb mor ddoeth: ‘Rydw i’n aros tan y gaeaf ac wedyn yn gyrru i lawr gyda ’nhractor a’r trelar ac yn casglu’r coed – maen nhw’n barod yn hwylus iawn i mi ar gyfer fy stôr o goed. Ac weithiau fe fydda’ i’n hela un. Fyddet ti’n hoffi cael afanc i swper nos fory? Mi dynna i un allan o’r rhewgell.’ Roeddwn i’n meddwl ei fod yn neis, wedi’i goginio’n dda, rhywbeth rhwng ysgyfarnog ac iwrch.

Roeddwn i’n hoffi’r ffordd ddi-lol yr oedd Erik yn byw gyda’r afancod ac roedd hefyd yn cydnabod eu gwerth i’r ecosystem tir gwlyb. Am y gwerth hwnnw y mae’r llyfr rhagorol yma’n sôn; mae wedi’i ysgrifennu gan 12 o arbenigwyr sydd wedi dod â chyfoeth o brofiad at ei gilydd ac, yn bwysicach, stôr o wybodaeth am sut gallwn ni ddysgu byw gydag afancod unwaith eto ym Mhrydain Fawr.

Rydw i mor falch bod afancod yn ôl yn ein gwlad ni oherwydd rydw i’n sylweddoli eu bod nhw’n hanfodol i helpu i reoli’r ecosystemau naturiol o dir gwlyb. Mae wedi cymryd amser maith – llawer mwy nag yr oeddwn i wedi’i ddisgwyl pan gymerais i ran yn y drafodaeth ddifrifol gyntaf fel aelod o fwrdd Scottish Natural Heritage nôl ar ddechrau’r 1990au. Mae arbrawf gwyddonol llwyddiannus wedi cael ei gynnal gan Gymdeithas Sŵolegol Frenhinol Caeredin ac Ymddiriedolaeth Natur yr Alban ar dir sy’n eiddo i Gomisiwn Coedwigaeth yr Alban, a gyda chyfraniad gwyddonol gan Scottish Natural Heritage. Mae afancod, oherwydd eu natur, wedi dod i’r golwg ar eu liwt eu hunain yn nalgylch Tay yn yr Alban hefyd, ac mewn mannau eraill ym Mhrydain yn achlysurol. Y gobaith ydi y bydd y llywodraeth yn gwneud penderfyniad yn fuan ac yn datgan y dylai’r rhywogaeth bwysig hon fod yn rhan unwaith eto o’n ffawna naturiol ni, ac y gallwn weld ei hadfer unwaith eto yn ei chynefin gwreiddiol.

Wrth i mi grwydro i astudio afancod a siarad gydag arbenigwyr ar afancod mewn gwledydd Ewropeaidd amrywiol, rydw i wedi synnu at eu gwybodaeth am y rhywogaeth a’u dealltwriaeth ohoni yn eu gwledydd. Maent yn defnyddio synnwyr cyffredin ac yn gweithio ac yn byw gydag anifail sy’n gallu synnu dyn ar adegau.

Mae tua chant o dudalennau i’w darllen yma ac fe gewch chi ddysgu popeth y mae arnoch angen ei wybod am hanes ac ecoleg afancod, eu heffaith ar weithrediadau dyn a’u gwerth yn yr ecosystem. Bydd adfer ecosystemau mewn byd mor fregus yn dod yn rhan fwyfwy canolog o’n hethos ni ym maes cadwraeth natur. Mae’r awduron yn ysgrifennu am sawl agwedd ar sut mae rheoli afancod a’u gweithgareddau; o reoli argaeau’n rhagweithiol i ddulliau newydd o leihau eu heffaith ar ein buddiannau ni. Ceir gwybodaeth am ddal, trawsleoli, difa a phynciau niferus eraill. Rydw i wedi bod o’r farn erioed bod rhaid wrth gyfundrefn reoli gadarn os am ddod ag afancod yn ôl ledled Prydain Fawr, ac os am ymateb yn gyflym i’r rhai sy’n gofyn am help wrth i afancod greu problemau iddynt.

Mae prif ran y llyfryn hwn yn cloi gyda dysgu byw gydag afancod, a hon fydd yr agwedd bwysicaf o bosib. Rydw i’n credu ei bod yn hanfodol i ffermwyr, coedwigwyr, pysgotwyr a phob un ohonom ni dderbyn y bydd rhai rhywogaethau’n achosi problemau i ni ar adegau, ond bod rhaid i ni gofio bod angen llu o rywogaethau a gweithredoedd ym myd natur er mwyn galluogi i ni ffermio a physgota, tyfu cnydau a choed, a chael dŵr ffres ac awyr iach i’w anadlu. Rydyn ni, fel yr afancod, yn rhan o’r ecosystem fawr yr ydyn ni’n ei galw’n Ddaear. Mae’n rhaid i ni ddathlu dychweliad y meistr ar beirianneg dŵr.

The authors would like to thank all those who have contributed to this collaboration. The information included here is a culmination of many years’ worth of field work, animal management and landowner experience. We are grateful for the additions from Thomas Borup Svendsen (Danish Ministry of the Environment, Denmark), Mike Callahan (Beaver Solutions LLC), Bryony Cole (University of Exeter), Sean Dugan (Scottish Fisheries Co-ordination Centre), Gidona Goodman (University of Edinburgh), Stuart Jenkins (RZSS), Robert Needham (University of Southampton), Romain Pizzi (Zoological Medicine), James Scott (SNH), Janne Sundell (University of Helsinki), Julia Coats (APHA), Kelsey Wilson, Ian McGowan (SNH), Colin Seddon (SSPCA), Glenn Iason (James Hutton Institution), Stefanie Venske (NaturErlebnisZentrum Wappenschmiede), Jika Uhlikova (Nature Conservation Agency of the Czech Republic), Ales Vorel (Czech University of Life Science) and Charlie Wilson. The images and photographs included have been vital to illustrate various aspects of this manual, so many thanks are given to all those who contributed, particularly Rachael Campbell-Palmer and Karlene Hill (SWT). Lastly, many thanks are given to those who edited earlier drafts of this manual, their contributions have been invaluable. Special thanks go to Nick Warren, Martin Gaywood (SNH) and Ivor Normand.

Beavers (i.e. the Eurasian beaver, Castor fiber, and the North American – sometimes referred to as Canadian – beaver, C. canadensis) are unique mammals that often capture people’s fascination. These are large rodents, with specialised features such as their flat scaly tails, and distinctive behaviours including tree-felling and dam-building. Few other animals, apart from humans, have the ability to modify so drastically their surrounding environments. Beavers play a key role in wetland ecology and species biodiversity, providing vital ecosystem services including habitat creation, water management and quality improvement, and sediment retention. At the same time, these beaver activities can also present real challenges for land and wildlife managers.

The history of the Eurasian beaver represents an important case study for conservation and reintroduction programmes. By the late 19th century, the once widespread Eurasian beaver was reduced to a handful of relict populations in fragmented refugia across Europe, in which potentially 1,000–2,000 individuals survived (Nolet and Rosell 1998). As beaver populations dwindled, so did the understanding of living with this species pass from common knowledge. In the beavers’ absence, landscapes continued to be altered by humans, and riparian environments in particular were engineered to suit agricultural and industrial needs. By the early 20th century, naturalists tended erroneously to believe that beavers were solely a species found in ‘open woods alongside rivers, old river beds and lakes’ (van den Brink 1967) and limited in distribution by habitat suitability.

Figure 1.1 Eurasian beaver feeding on water lilies at the Scottish Beaver Trial. (P. Price)

Since then, Eurasian beavers have been restored to much of their former native range through proactive reintroductions and translocations (Halley et al. 2012). Contemporary experience of expanding beaver populations across Europe and North America demonstrates clearly that beavers can readily modify even heavily engineered landscapes to suit their own ecological requirements. The two extant beaver species, the Eurasian and the North American, inhabit wetlands and water bodies from north of the Arctic Circle, where they can endure five months of darkness and ice, to the everglades of subtropical Florida. The dry, arid environment of the Ulungaur watershed in Mongolia contains one of the last remaining Far Eastern beaver populations. Intensively utilised, cultural landscapes dominated by agricultural production with amenity woodlands, recreational areas and engineered water bodies are relatively unchallenging environments for beavers. Although it has been well demonstrated that environmental factors such as topography, hydrology and vegetation influence beaver distribution (Schwab et al. 1992; Rosenau 2003; Rosell et al. 2005), they are clearly a much more adaptive species than was initially believed.

The Eurasian beaver is a well-studied species capable of providing biodiversity and economic benefits through its natural activities. Its restoration is considered internationally to be a clear conservation success (Halley and Rosell 2002). While initially some countries (such as Finland and Russia) restored beavers to support a commercial fur trade, the majority of recent reintroductions have been implemented for nature conservation purposes. This emphasis has been prompted by a greater awareness of the ecological benefits which accrue from the presence of beavers.

The return of the beaver through a combination of reintroductions and natural recolonisation has often been viewed as a novel phenomenon. When beaver populations initially re-establish, the physical impact of their activities is often confined to a small group of land-users such as farmers, foresters or water authorities (Siemer et al. 2013). As beaver populations increase, the novelty of their presence can be replaced by hostility from wider elements of society when more visible impacts occur such as the felling of specimen trees in public parks, orchards or gardens. It is inevitable that a process whereby people ‘rediscover’ what it means to live with beavers will become a critical component of coexistence. Understanding, tolerance and a willingness to manage undesirable aspects of beaver activity competently will also be of fundamental importance.

Figure 1.2 Beaver-occupied site (>20 years), Norway. The beaver lodge is located on the small islet near the centre of the photograph. The lodge is 2 km downstream from a hydroelectric dam so water levels can vary abruptly. Although beaver signs are evident on the ground, the overall tree structure remains largely unaffected, and many people are unaware of the beavers’ presence. (D. Halley)

Figure 1.3 Tree-coppicing near the Deutsches Museum, in downtown Munich, an area first occupied by beavers around 2000. (R. Campbell-Palmer)

Figure 1.4 Signs of beaver activity along an urban canal (Freising, Bavaria) where house-owners regularly feed beavers. (R. Campbell-Palmer)

Figure 1.5 Beaver-created wetland habitat in agricultural areas in Bavaria. Various beaver-management techniques may be required, especially in modified environments. These may include flow devices, fencing, land purchase for conservation, trapping and removal. Where these can be planned and implemented, beavers can diversify an area and provide biodiversity hotspots in close proximity to other human land uses. (R. Campbell-Palmer)

This handbook considers a broad range of issues which are likely to arise over time as beavers are re-established, particularly with respect to British landscapes, but also elsewhere in Europe. It affords a practical overview of the implications of beaver restoration and the management requirements. Most of the information presented here addresses the experiences gained from beaver restoration in Europe, but draws from practical experiences in North America where beaver populations have also recovered. The handbook describes the animals’ field signs, lifestyle, their effects on the environment and appropriate mitigation techniques, as supposed to any wider-scale, long-term management strategy at a national level. In relation to Britain, the Eurasian beaver has not yet been formally reintroduced despite being an Annex IV species on the European Habitats Directive, although licensed trial reintroductions have occurred in Scotland (Scottish Beaver Trial) and most recently in England (Devon Beaver Trial). If the decision is made that beavers should remain, then it is anticipated their domestic legal status will change, and management strategies will be developed. We recommend that advice and necessary permission should be sought from the appropriate Statutory Nature Conservation Organisations (SNCOs) before employment of any mitigation measures.

Key concepts

•Beavers modify their environment and play a key role in wetland ecology and biodiversity.

•Beavers have been restored to much of their former native range from near-extinction following human exploitation.

•Understanding of beaver ecology, tolerance and a willingness to competently manage undesirable aspects of their behaviours are fundamental to living with this species again.

•This handbook discusses the implications of beaver restoration and likely management requirements in a British context.

‘The church … the mill, bridge, salmon leap, an orchard with a delightful garden, all stand together on a small plot of ground. The Teivi has another singular particularity, being the only river in Wales, or even in England, which has beavers. In Scotland they are said to be found in one river, but are very scarce.’ Giraldus Cambrensis (1180)

The above quotation describes a British landscape, moulded by people to suit their needs, which was also occupied by Eurasian beavers. The salmon (Salmo salar) leap, where fish could be harvested for consumption during their annual migration, offers a tantalising clue as to why the Eurasian beaver may have survived on the River Teivi at a time when it had otherwise become such an unfamiliar species in a British landscape. In 10th-century Wales, a beaver pelt was worth 120d (pence), and a pine marten (Martes martes) pelt 24d, while Eurasian otter (Lutra lutra), Eurasian wolf (Canis lupus lupus) and red fox (Vulpes vulpes) pelts were worth 8d each (Rodgers 1947–48). Did this community, which successfully managed its fish, also tolerate beavers for the prospect of a similar and profitable annual harvest?

The Eurasian beaver is a native species which was once widespread in freshwater habitats throughout Britain. Fossil records indicate that beavers were present in Britain 2 million years ago – and archaeological evidence, including gnawed timber, dams, lodges, burrows and bones, has been recorded from a number of sites (Macdonald et al. 1995; Coles 2006). Various place names, illustrations and other references bear testament to the former presence of this animal (Coles 2006). In 1837, the nearly complete skeleton of a beaver was found in a hole in the bank of the River Stour, near Keynston Mill in Dorset.

Eurasian beavers were hunted to extinction in Britain for their castoreum (a secretion from their castor glands with supposed medicinal properties, used by beavers in chemical communication), meat, fur and other body parts such as jaw bones. By the 15th century, the trade in their fur was no longer economically viable due to overexploitation, and their presence began to fade from folk memory. Oral traditions of their presence on Loch Ness and in Lochaber in Scotland, and in the Ogwen Valley in Wales, lingered on until the end of the 18th century (Coles 2006). Some of the latest physical evidence of beaver presence in Britain is a beaver-chewed stick carbon dated to 1269–1396, which was found in the upper Tyne catchment (Manning et al. 2014). While we will never know when the last British beaver was killed, a church ledger record from the village of Bolton Percy near York in 1780 records the payment of a bounty of tuppence for the head of a beaver (Coles 2006). No other references to the species’ survival beyond this date are currently known.

Figure 2.1 Beaver-related place names exist throughout Britain. (D. Gow)

The concept of reintroducing beavers to mainland Britain (they are not known to have ever been native to Ireland or any of the outer isles) is not new. Their restoration has been widely discussed in both the general media and academic literature. Despite recommendations for a more comprehensive process of restoration (Gurnell et al. 2009), the return of the beaver has been a haphazard affair. At the time of writing, two officially licensed trial beaver releases into the wild exist: the Scottish Beaver Trial in Mid-Argyll, and the Devon Beaver Trial on the River Otter, Devon. The Scottish Government is due to consider the results of the trial and make a final decision on the future of beavers in Scotland (expected some time in 2016). Additionally, in the mid-2000s it became apparent that a sizeable population of unlicensed wild beavers were distributed throughout the catchment of the Rivers Tay and Earn in Perthshire, Scotland (Campbell et al. 2012a). In England and Wales, there is scattered evidence from field signs and photographs of the existence of small numbers of free-living wild beavers. Wild beavers are therefore already present in Britain. There are also a growing number of enclosed populations, and there are proposals for further trial releases in England and Wales (e.g. Welsh Beaver Project). Unless British governments decide to remove these beavers their populations will increase and their distribution expand. An understanding of their management requirements will therefore become a necessity.

Lord Onslow, writing in the Countryman magazine in 1939, suggested that as the ‘beaver have become extinct in England only within the last few centuries … there seems no reason at all why they should not be reintroduced’ (Onslow 1939). In 1994, Scottish Natural Heritage (SNH), Natural England (then English Nature) and Natural Resources Wales (then Countryside Council for Wales) began to consider the potential for restoring beavers in Britain. To date, this process has progressed furthest in Scotland, with an official trial reintroduction and the scientific study of the larger unlicensed population in Tayside, though the Devon Beaver Project was given a licence for a five-year scientifically monitored trial release on the River Otter in 2015.

In 1998, SNH launched a public consultation to ascertain wider attitudes to beaver reintroduction in Scotland (SNH 1998). While the majority of respondents favoured reintroduction, there were concerns and opposition expressed by others who feared that beaver activity would have detrimental impacts on farming, fisheries and forestry. In response to these findings, SNH took the decision to develop a time-limited, trial reintroduction in the Forestry Commission Scotland (FCS)-managed Knapdale Forest in Mid-Argyll, to explore the feasibility of releasing beavers and to study their impacts. Although an initial SNH licence application (2002) was turned down in 2005 by the then Scottish Executive, a joint licence application submitted in 2007 by the Scottish Wildlife Trust (SWT) and the Royal Zoological Society of Scotland (RZSS) was successful. This led to the development of the Scottish Beaver Trial, the first licensed and unfenced reintroduction of Eurasian beavers (and in addition the first official mammal reintroduction) in Britain.

Figure 2.2 Beaver pair released as part of the Scottish Beaver Trial. (Scottish Beaver)

Figure 2.3 Camera-trap image of wild beaver on the River Otter, England. (T. Buckley)

Although to date the reintroduction process has progressed furthest in Scotland, feasibility studies on beaver reintroduction to Wales (Halley et al. 2009) and England (Gurnell et al. 2009) have been published. Since the first release at Ham Fen in Kent in 2002 (Campbell and Tattersall 2003), breeding populations of beavers have been established in large enclosures at several locations in England, Scotland and Wales. One example of a well-studied project of this type is the demonstration site established in 2011 in the upper watershed of the River Wolf which has been developed by the Devon Wildlife Trust (DWT 2013). These controlled projects can provide useful information when employed specifically to assess the role of beavers as habitat-modifiers and as tools for landscape management or stakeholder engagement.

Key concepts

•The Eurasian beaver is a native mammal to Britain, and was once widespread.

•Beavers were hunted to extinction for their meat and fur, and were largely extirpated by the 16th century.

•Beaver reintroduction has a long history in Britain. Currently, there are two licensed trial releases (Mid-Argyll and Devon), with free-living beavers present in Perthshire and parts of England.

The Eurasian beaver and the North American beaver are the only surviving members of the once larger family of Castoridae. Both modern beaver species are physically very similar, making them hard to distinguish in the field. They have very similar ecological requirements and behavioural patterns, and were once considered to be a single species. Chromosome analysis has identified that the Eurasian beaver possesses 48 pairs of chromosomes, while the North American beaver has 40 (Lavrov and Orlov 1973). As a result, the two species will not interbreed and produce viable offspring, even when attempted through captive breeding. Through differences in tail shape and subtle differences in their pelage, beaver species can be determined on closer inspection. Examination of the anal gland secretions provides reliable differences in colour and viscosity which can be used to determine beaver species and sex (Rosell and Sun 1999). It is now believed that divergence occurred about 7.5 million years ago when beavers first colonised North America from Eurasia across the land bridge of the Bering Strait (Horn et al. 2011). From the Eurasian fossil record of the Early and Middle Pleistocene (~2.4–0.13 Ma ago), in mature rivers and wetlands, modern beavers appear to have lived alongside, or possibly to have been locally excluded by, the slightly larger extinct beaver Trogontherium cuvieri; the prevalence of the two forms at archaeological sites demonstrates an inverse relationship (Mayhew 1978).

By the 16th century, Eurasian beavers were largely extinct across most of Europe and Asia. At its lowest population point, it is believed that the Eurasian beaver in its western range was reduced to 200 animals on the River Elbe in Germany, 30 on the River Rhone in France and ~100 in Telemark, Norway (Nolet and Rosell 1998). Since the 1900s, beaver numbers have recovered throughout much of their former European range as a result of a combination of legal protection, hunting regulation, proactive reintroductions/translocations and natural recolonisations. Breeding farms that produced beavers for commercial fur farming, and later for release into the wild for restocking, were established at Voronezh (Russia) and Popielno (Poland) in 1933 and 1958, respectively (Jaczewski et al. 1995). The first official conservation translocation occurred from Norway to Sweden in 1922, and since then there have been more than 200 recorded translocations of beavers (Halley et al. 2012). Eurasian beavers have now been restored to over 24 countries in Europe (Halley and Rosell 2002) and are currently estimated to number over 1 million individuals globally (Halley et al. 2012).

Figure 3.1 Current distribution of Eurasian beaver (red) and North American beaver (green). Black represents refugia where Eurasian beavers were never extinct (numbered west to east); ‘F’ indicates countries where reintroduction feasibility studies have been conducted. (Updated from Halley, Rosell and Saveljev 2012)

Also notable is a sizeable population (~8,000) of introduced North American beavers in Finland (Kauhala and Turkia 2013) and northwest Russia. In 1937, seven North American beavers from New York State, USA, were introduced to Finland to supplement an ongoing reintroduction of the nearly extinct Eurasian beaver there (Lahte and Helminen 1974). At that time, most zoologists recognised only one species of beaver worldwide (Parker et al. 2012). North American beavers are now also present in small numbers in parts of Belgium, western Germany and Luxembourg, as a result of escapes from a zoo and game parks (Dewas et al. 2012). Due to the significant biological and ecological similarities of these two species, identification and removal of the non-native North American beaver is important, requiring active management and resource investment (Parker et al. 2012).

Eurasian beavers are large (adults >20 kg), semi-aquatic, herbivorous rodents with a head and body length of ~80–100 cm and a tail length of ~30 cm on average in adults (Żurowski and Kasperczyk 1988), making them the second largest rodent species in the world. Beavers do not attain adult size until around three years of age. Adults of both sexes have similar head and body lengths, although females are on average 1–1.5 kg heavier than males, and are impossible to distinguish visually unless a female is heavily pregnant or lactating, during which time nipples will be visible (four under the forelegs).

Coat colour is usually brown but can range from pale golden to black. The beaver’s flattened tail is probably its most distinctive feature, covered in visible scales and dark grey in colour. When moving on land, beavers normally walk on all fours, although they can walk upright on their hind legs for very short distances when carrying mud or vegetation, particularly when building or restoring lodges for winter. During feeding sessions, they can be observed resting on their back legs while holding food in their forepaws. Beavers have small ears but have good hearing. Their eyesight is poor and largely functions to identify and respond to movements. They have an excellent sense of smell, and their chemical communication abilities are highly developed (Campbell-Palmer and Rosell 2010). While swimming, they utilise their powerful, webbed hind feet in a coordinated kicking motion for propulsion through the water and their tail as a steering rudder (Wilsson 1971; Novak 1987).

Beavers live in family groups, usually comprising an adult breeding pair with their offspring from the current and the previous year’s litters. Once paired, beavers tend to remain together until one partner either dies or is displaced by another individual of the same sex in territorial disputes. Mating usually takes place late December to February (depending on location). After a gestation of 105–107 days, the female gives birth to one litter per year, typically of one to four kits, in spring/early summer (with some geographical variation). The number of kits produced, and their survival, is affected by various factors such as the age of parents, the surrounding population density and habitat quality and altitude (Novak 1987; Campbell 2010; Campbell et al. 2013). Beaver kits are born fully furred, and usually weigh between 300 and 700 g. Their eyes are open soon after birth; and, although they will feed on their mother’s milk for 2–3 months, they can consume vegetation after their first week. The kits remain in the lodge for approximately the first 1–2 months of their lives while their parents and older siblings bring leafy twigs and other vegetation for them to eat. By the time they are approximately 2 years old, they have become sexually mature and usually disperse in order to attempt to establish territories and partners of their own (Wilsson 1971).

Although some beavers remain with their family units as non-breeding individuals for many years, particularly if there is a lack of suitable habitat to move to (Campbell et al. 2005), most 2 year olds will begin to search for territories of their own in the spring. During this period, they are capable of travelling long distances along water bodies and may undertake shorter trips overland. Beavers do not like to be far from the water or to travel over open land for large distances, though reports of individuals up to 11.7 km away from water exist these are rare (Saveljev et al. 2002); the barrier effect of watershed divides on beaver colonisation varies depending on topography (Halley et al. 2012). There is no consistent difference in dispersal between the sexes (Saveljev et al. 2002; McNew and Woolf 2005), and individuals will commonly make exploratory excursions into neighbouring areas (Campbell et al. 2005). After dispersal, they have been recorded taking up residence in some unconventional aquatic habitats, such as small ornamental ponds or sewage-treatment plants. The dispersal process can be hazardous for beavers, with deaths via road traffic accidents or through infections from wounds caused by other beavers. Beavers from one family are highly intolerant of those from other families and will fight aggressively with intruders. During these fights, deep, penetrating wounds are frequently inflicted by biting to the shoulders, flank and tail (Figure 3.4). Such wounds can result in severe injuries and/or become septic, and can result in death (Piechocki 1977).

Figure 3.3 Mother and ~3-month-old kit. (S. Gardner)

Figure 3.4 Crescent-shaped scarring from beaver bites inflicted during territorial disputes on the underside of a tanned beaver pelt. (R. Needham)

Eurasian beavers occupy freshwater bodies (ponds, streams, rivers, marshes and lakes) throughout much of Europe. Populations are still scattered in western and southern regions of this range. In Asia, there are relict populations in China (Xinjiang) and in Mongolia. The species is expanding rapidly in both distribution and numbers (Halley et al. 2012). Although they are highly adaptable and can modify many types of natural, cultivated and artificial habitats, they prefer still or slow-moving water with stable depths of at least 60 cm (Gurnell et al. 2009). Where these habitats are unavailable or are already colonised by other beavers, they will colonise narrower watercourses and construct dams to create suitable habitat.

Although the average size of a beaver territory is approximately 3 km of shore length, size can vary greatly depending on habitat quality, particularly winter food resources, from 0.5 to 20 km of shore length (Macdonald et al. 1995; Herr and Rosell 2004; Campbell et al. 2005). During the Scottish Beaver Trial the total length of waters’ edge used by each beaver pair or family ranged from 1.8 to 4.7 km (Harrington et al. 2015). The extent and character of a territory is also affected by the surrounding density of the beaver population.

Figure 3.5 Newly created wetland through beaver dam-building activity at the Devon Wildlife Trial site. (D. Plummer)

It is a common misconception that suitable beaver habitat solely comprises large tracts of wet woodland. In developed landscapes, they will readily exploit any palatable vegetation in close proximity to water bodies such as mown amenity bankings, grass verges, grazing pastures or agricultural crops. In climates that experience prolonged winters below freezing, access to woody browse in order to collect a cached food reserve is, however, an essential, limiting factor in survival and population growth.

Beavers are entirely herbivorous and will readily consume a wide range of bark, shoots and leaves of woody plants (majority broadleaf species), as well as herbaceous and aquatic vegetation. During spring and summer, up to 90% of their diet is composed of terrestrial, semi-emergent and aquatic species of plants (Nolet et al. 1995), though it can be under 30% in Norway (Campbell et al. 2013). Although beavers can fell quite large trees (>1 m in diameter), they tend to favour smaller saplings (<5 cm diameter) in order to obtain their bark, side branches and leafy stems (Haarberg and Rosell 2006). Favoured woody plant species include aspen and poplar (Populus spp.), willow (Salix spp.) and rowan (Sorbus aucuparia), while alder (Alnus glutinosa) is generally avoided (Fustec et al. 2001; Haarberg and Rosell 2003; Iason et al. 2014). Foraging generally takes place close to the bank; in Denmark, for example, 95% of beaver-cut stems were within 5 m of water (Elmeros et al. 2003); in Norway, 70% of cut stems were within 10 m and 90% within 20 m (Haarberg and Rosell 2006); in Russia, 90% of cut stems were within 13 m of water and 99% within 20 m (Baskin and Sjöberg 2003). Similarly, findings from the Scottish Beaver Trial determined that most foraging activity on trees occurred within 10 m from the waters’ edge (Iason et al. 2014).