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Saturday, 26 March 2016

New kits on the block

A packed room heard about DWT's River Otter Beaver Trial (ROBT) from Project Officer Mark Elliott at our event on 16 March. For more details about the ROBT, the best source of latest and background news is probably the DWT webpage link here.

A few months ago we made a trip to see if we could spot the beavers. An account of that visit, adapted from an article in the latest Devon Mammal Group newsletter, is below.

New Kits on the Block from Devon Mammal Group newsletter winter 2015

Devon’s mammal specialities, a ‘Devon Big 5’, might include otter, dormouse and greater horseshoe bat. And now emerging into the limelight from not much more than a rumour a couple of years ago, east Devon’s beaver population is a new, high profile, species on the block.

But notwithstanding all the media coverage, a candidate iconic county species should have at least a chance of being glimpsed; so just how easy would it be to see the River Otter beavers, wild-living and in the fur? On a summer's evening, Devon Mammal Group members met to find out at a suggested River Otter location, a site visit kindly hosted and led by Mark Elliott, Devon Wildlife Trust’s project officer for the River Otter Beaver Trial.

Those used to getting waterlogged waders and nose down into murky water peering after otter spraint would be relieved. A first immediate observation, mere metres from the car park, was that some beaver field signs are refreshingly obvious. Mark showed us some classic ‘pencil sharpenered’ willow stems, and a regularly visited tree with a wheal of peeled bark above a talus of beaver chips.
Mark explains how some beaver field signs can be subtle
Other signs however are more subtle and need more practice to recognise. For example, a nibbled lawn of grass and herbaceous vegetation (which beavers feed on during summer); a single floating branch snagged on a bridge and exhibiting the characteristic 450 angle snipping at one end (think enormous water vole); and pale-de-barked patches on a root bole where past willow sproutings has been gnawed off, or one might say coppiced, at water level.
Beaver  nibbled willow - note paler bare patches where stems have been gnawed away
From visits to Knapdale to see the Scottish trial beavers, and to the enclosed site in North Devon, impacts on the landscape by ecosystem engineering beavers can be dramatic. It suggests that in time evidence of beaver workings on the River Otter would become more apparent, but how much time? It’s estimated beavers have been on the river since around 2002-3, but so far they've left hardly an impression over 10 years or more. This is plausibly because living at such low density, and also because, as a deeper watercourse, beavers have not been stimulated to build dams on the main river to create their required deep water conditions. So far the River Otter looks like many other rural Devon rivers, with vegetated banks bordering agricultural fields, and no particular inkling that it might be harbouring a population of celebrity beavers. 

Experience of reintroduction schemes elsewhere in Europe suggests reintroduced beavers are perfectly able to inhabit and colonise a modern farmed landscape. In 1900 the European population numbered around 1200 animals; by 2003 this was up to 639,000 (*). With dusk gradually gathering, what would be our chances of seeing the only officially wild-living beavers in England? 
Spot the beaver, in prime Devon habitat. Beavers eat Himalayan balsam
Two groups of beavers are known: one around Ottery St Mary and the other at Otterton. An individual spotted further north around Honiton in autumn is thought to be a dispersing 2 year old sub-adult from one of these family groups. Genetics have revealed both groups originate from a single adult pair; a male found dead 2-3 years ago near Fenny Bridges is the conjectured father. Since then the increasing population (9 animals prior to the birth of 2015’s kits) has been the result of a certain amount of inbreeding. This may not be as fatal a shortcoming as first seems, as inbreeding sometimes happens in wild beavers. Modelling studies have calculated 25 pairs to be the minimum viable population, though in practice 6 pairs have led to sustaining colonies on the Rhรดne and 22 animals in Moravia (**). Nevertheless the DWT licence allows additional animals to be introduced to boost the genetic health, an option currently being explored. 

Just how dramatic any changes to the river corridor might be is a question to be covered by the monitoring programme associated with the other terms of DWT’s licence. Over the next 5 years DWT will be measuring the impacts on geomorphology and hydrology of the river, on neighbouring agricultural land, and on other species; understanding the beavers’ population dynamics and use of the landscape; developing ways of managing conflict situations (and for which there must be an ultimate exit strategy in place for the eventuality that the beavers must be removed); and public engagement and attitudes. Serious concerns are that migrating fish might be prevented from reaching spawning grounds by beaver dams, and that river banks may be undermined by beaver burrows, leading to flooding of farmland.

Public sightings may be an important part of monitoring and, to help with identification, the adults and some of the kits from each of the family groups are marked with coloured ear tags. It will be fascinating to see how far, and how fast, the beavers go, literally and figuratively into uncharted new territory.

This first taster expedition proved a success. Arriving at a copse of willows, we crouched down to watch an adult with a red ear tag – the female from the Ottery St Mary group - nibbling at some vegetation on the river bank. A kit swam in unhurried circuits in front of us several times, before silently executing a forward roll dive out of sight into the water, without a splash and barely a ripple. 
New for 2015. Photo with thanks to (c) Geoff and Emma-rose Goodwin.

(*) D Halley & F Rosell 2003 Population and distribution of European beavers Castor fiber Lutra 46 (2): 91-101. This paper was published 2003 so it might be anticipated the European population is now more than 639,000 

(**) D Halley, F Rosell & A Saveljev 2012 Population and Distribution of Eurasian Beaver (Castor fiber). Baltic Forestry 18 (1): 168-175 
J Frantisek, S Baker & V Kostkan 2010 Habitat selection of an expanding beaver (Castor fiber) population in central and upper Morava River basin. European Journal of Wildlife Research 56 (4) 663-671

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