Reintroductions as an essential conservation tool for water vole populations

In this article, Derek Gow (Director of the Derek Gow Consultancy Ltd) looks at the issues surrounding water vole decline and successful reintroduction…

“Beyond the Wild Wood comes the wild world” said the Rat.“And that’s something that doesn’t matter, either to you or to me. I’ve never been there, and I’m never going’ nor you either, if you’ve got any sense at all.”

Kenneth Grahame, 1908.

Introduction
It is quite chilling how “Ratty’s” quote regarding his own limits of vision of this, his wider world, in the timeless classic the “Wind in the Willlows”, now so aptly parallels the calamitous shrinkage in prospect for his species in Britain.

Although water voles (Arvicola amphibious) have never been a widespread woodland creature, a wealth of modern experience demonstrates that they are much more adaptable and robust than we formerly realised. Despite this, as a common feature of canals, streams, farm ponds, roadside ditches, rivers, wetlands and other riparian edge habitats they had, by the late 1990’,s becoming tantalisingly difficult to observe. While our earlier formed perception of abundance could well have been shaped by the passing of Victorian times when most of their predators were savagely eliminated; when wetland tree cultivation for a plethora of reasons was largely abandoned to shade out their verdant, water’s edge habitats or when the jollity of village ‘water rat’ hunts where crowds of drunken worthies on a Saturday afternoon with their attendant curs, bashed the banks and clubbed their fleeing inhabitants to death, these factors were within our lifetimes still relatively restricted hazards. The landscape changes of the late 20th century, whereby state subsidised programmes of landscape drainage on an industrial scale, coupled with the canalisation of rivers and water courses, the blanket coniferisation of the uplands, a prodigious intensification in numbers of grazing livestock, the merciless expansion of pesticide-laden arable crops right up to the very edge of water courses and the establishment of North American mink (Neovison vison) – a non-native predator, which hunts them in a way no native carnivores effectively emulate – all in tandem reduced the once common water vole to a shadowy vestige of its former self. This common understanding of water vole decline and loss is, however, still crude and commonly ignores the clear body of evidence which indicates that water voles in prehistoric, historic and even contemporary times displayed a ready ability to exist in the wider environments beyond the banks of the rivers bounds. Fossorial water vole populations, which are utterly unconnected to any water bodies, still remain in Glasgow living out their subterranean existence in road-side verges and traffic islands. The same form may still survive on Bartsea Island and more modern anecdotal records exist of their continued presence in the far north of Scotland, in Wales and in scattered locations in southern England (Stuart, R. Personal communication).

When I began my work with water voles in the early 1990’s with a view to establishing captive breeding programmes, which could in time produce sufficient individuals for tentative trial and later larger landscape scale releases, I believed that I was dealing with the delicate relict of a fragile entity. My emphasis on captive breeding and reintroduction was a side-show when set against an alarming background need for immediate intervention to save dwindling colonies from habitat decline, mink predation and the wider education of land users. Considerable financial and logistical resources to address these demands were assembled, but while some strategies met with success, many failed and the national population of water voles as calculated at the time of their legal protection in Britain in the early 2000’s of 1.2 million, has now fallen to less than 300,000. While a vast amount has been learnt regarding the species biology, mink control, habitat manipulation and effective conservation, there is no credible way that these figures can represent success. In a time of acute financial stringency, funding apathy with regard to the species plight and elements of a strongly unimaginative approach to its future conservation, which simply seek to revert to the repetition of past failure, there is an urgent need to think again. This thought process and its actions which follow must involve learning the lessons of both success and failure.

The water vole
Although the northern water vole was famously employed by Kenneth Grahame as the basis for his character of Ratty in “Wind in the Willows” the species was commonly portrayed in other children’s books of a similar time frame as largely avuncular; it was a bumbling, benign character with a simple but well meaning disposition. Although water voles were widely referred to as “water-rats” they were once accorded a variety of other titles such as Crabers, Water dogs, British beavers and Campagnols (Ryder, 1962). In parts of Aberdeenshire, the terrestrial black form commonly was called an “Earthhound” and was believed to inhabit graveyards in order to abduct the souls of the dead!

The water vole is the largest of the three vole species native to mainland Britain. Mature adult males can weigh up to 360g in England and in the region of 260g in upland environments in Scotland. While British water voles normally inhabit riparian fringe habitats and are seldom found in substantial landlocked populations, this phenomena is unusual in a European context and may have much to do with the historic intensity of land use by people. Water voles are generally vegetarian – although instances of the consumption of fish carrion and cannibalism have been observed – and have been recorded feeding on wide range of plant species (Strachan, R. 1999). In the spring and summer months they favour the more easily available, sugar rich grasses, reeds, rushes and sedges before a changing winter emphasis selects roots, rhizomes and tubers which are hoarded as food reserves in their underground burrow chambers. In southern Britain water voles will be active during periods of milder weather even in the winter months. Their burrow systems, which have underwater entrance and exit holes and nesting chambers lined with shredded dry vegetation, can be of significant age. In peat and heavy clay soils they remain in-situ as features for many decades, with succeeding generations of water voles essentially occupying, modifying and enlarging the haunts of their ancestors.

As complex underground structures, they are widely utilised by a range of other small mammal species, reptiles, amphibians and insects as refugia. Where water voles have been present for many years in an environment, the undermining effect of their burrow systems will result in bankside collapses which, in smaller water courses, can change the character of meanders or establish new pools. On a larger scale they can expose open ‘walls’ of bankside substrates. Features of this type can then in turn be exploited as nesting habitats by bird species such as kingfishers (Alcedo atthis) and sand martens (Riparia riparia) or maybe even bee-eaters (Merops apiaster) in time. They are additionally utilised by burrowing insects. Studies undertaken in Glasgow of the burrow systems of fossorial water voles using ground penetrating radar have also identified large, complex underground structures which could credibly be of significant age (R. Stuart. Personal communication).

Water voles are a highly fecund species. In abundance in Europe they provide a broad range of high quality prey for species such as wildcats (Felis silvestris) and other larger terrestrial carnivores. When they were formerly abundant in Britain it is inconceivable that their presence did not provide the same function. They are currently, even in their diminished state, a known prey component of red foxes (Vulpes vulpes), polecats (Mustela putorious), otters (Lutra lutra), stoats (Mustela erminea), pike (Esox lucius), golden eagles (Aquila chrysaetos), marsh harriers (Circus aeruginosus) and grey herons (Ardea cinerea).

In summer, emergent burrow entrances are commonly surrounded by evenly mown ‘vole lawns’ within easy reach of their perimeter. Where water voles are present at high densities, their grazing and re-grazing at intensity of the vegetation will alter the plant structure in the surrounding environment. Some plant species such as yellow flag iris (Iris pseudacorus) are adapted to the untidy nature of water vole feeding activity, which acts as a dispersal mechanism for viable sections of rooted, tuber fragments or its buoyant seeds. In seasonally occurring reed beds where burrowing is not possible, football sized nests constructed from intricately woven vegetation can be constructed above the normal water level. These structures have been readily created in rush clumps by captive bred animals within a short period of their release. Water voles can mate on the land or in water and will normally produce an average of around 20 offspring per annum in captivity. Field signs of water vole presence such as stems of plant material cut at a distinctive 45-degree angle, latrines, feeding platforms, tracks, runs and burrows are easy to observe where they are common.

Stephanie Ryder writing in 1962 stated that “wherever there is good water contained in firm banks …………you may be sure to find signs of water vole habitation” and until comparatively recently this was still widely perceived to be the case. In 1990 a series of national surveys funded by the Vincent Wildlife Trust (Strachan & Jeffries, 1993) identified a serious constriction in the national range of the water vole and subsequent repeat surveys (Strachan, Strachan & Jeffries, 2000) now suggest that this species may have disappeared from over 97% of its former range.

This steep decline is linked directly to the intensification of agricultural practice over the course of the last century. Extensive wetland drainage, increasing densities of livestock overgrazing riparian vegetation and arable cultivation to the edge of watercourses have been coupled with substantial river, stream or ditch canalisation programmes and unsympathetic annual dredging regimes. The impact of these processes has been further compounded by bank-side reinforcement programmes employing concrete or metal pilling, the successful colonisation of introduced North American mink and an associated range of further incidental factors such as accidental poisoning or sporadic human persecution.

As a result of the above, water voles are now legally protected under Schedule 5 of the Wildlife and Countryside Act. This legal protection, although preventing their reckless destruction, has done little to halt their continued decline. The national distribution of this species is now highly fragmented and in many counties they are already extinct. Current predictions are that this situation will worsen leading to further widespread extinctions. Where extensive populations of water voles still occur in suitable habitats in lowland England, species recovery incentives such as those focused on the coordinated control of North American mink by the Essex Wildlife Trust, have led to a significant recovery of water vole populations (D. Tansley. Personal communication). In the Mountain uplands of Scotland where a programme of highly effective mink control has been developed and maintained by the Scottish Mink Initiative (Lambin. X. Personal communication), the natural range recovery of highly fragmented water vole populations from sub-optimal habitats has been imperceptible. Where significant vole populations are no longer extant a more active process of restoration to support, restore and rejoin relict populations will be essential. Contemporary experience now indicates that the species cannot re-colonise lost landscapes where they are not present elsewhere in a linked riparian environment in significant numbers. In environments of this type this once familiar denizen of the countryside will be reduced to the lingering relict of a camphored museum specimen.

Captive breeding water voles
It is against this background that water vole restoration utilising either translocated animals or captive bred offspring has become an identified component of the species recovery, as recommended in the 3rd Water Vole Conservation Handbook (Strachan et all, 2011). Water vole translocations (the direct movement of wild caught animals from one site to another) – which have commonly been practised as a component of human development projects – are problematic (Gow, Holder and Jeffrey, 2004) and have commonly failed or resulted in an indeterminable result. Although a more recent translocation of non-captive bred individuals coordinated by the Essex Wildlife Trust and the DGC has resulted in the establishment of a large, vigorous expanding water vole population in the landscapes surrounding the Trust’s Thorley Wash Nature reserve in the headwaters of the River Lee, this involved the translocation of a substantial initial population (Tansley. D. Personal communication). These were obtained from a number of development sites in 2015 which were located throughout southern England. The captured individuals were either then released into Thorley wash in the spring of 2015 or, if captured in the autumn, held over winter in captivity and released in the spring of 2016. Many were paired in their release pens with unrelated mates while the ages and sexes of all the individuals were known.

The first large scale water vole breeding project began in 1994 at the New Forest Nature Quest, with the express aim of developing a sustainable methodology for reproducing this species consistently. Although breeding attempts had been successful in a study population at Queen Mary and Westfield College (Blake, 1982), no effort had been made to reproduce this short-lived species in sufficient numbers to render reintroductions possible. Even though this was not a conservation priority action at that time, it is a fundamental error in any recovery process for an endangered species to leave the development of a captive breeding component until individual founders are in short supply. Genetic diversity will by this stage be extremely low and if husbandry protocols have to be developed from scratch, any resultant human errors can be critical to the survival of the species (Durrell, 1992). For this reason captive breeding as a component of an overall conservation package is best refined when an initial threat is perceived as part of any process of general biological research.

The first breeding attempts at Nature Quest were with animals captured from fish farms on the River Itchen in Hampshire. These were contained in large landscaped pens, which were 30ft in diameter with pools, selected food vegetation and adequate burrowing banks. The retaining walls of these enclosures were constructed of 4ft high sheet tin and they were under-wired to a depth of 2.5ft with half-inch weld-mesh. Despite this last adaptation, voles readily burrowed out and on one occasion a female which escaped in late summer and survived outside over-winter, returned of her own accord to breed in the spring. Although these pens were stocked with various combinations of animals, we now know that they will only successfully contain a single breeding pair and their resultant offspring. Any other combination of breeding adults confined together in the spring inevitably results in severe fighting to the point of extreme disability or death. This negative experience of mixing unrelated groups of adult individuals was replicated in a trial release project developed by the Wildfowl and Wetlands Trust at Slimbridge, where severe aggression resulted in the swift collapse of a substantial confined population (Strachan, C. Personal communication). As an initial project objective was to maximise potential reproduction, this enclosure design was eventually abandoned for all purposes except public display.

A further series of smaller breeding pens were trialled before the final prototype that is currently employed emerged. These are wooden framed cages (6ft long by 4ft high by 4ft broad) with solid wooded floors. They are meshed throughout with half-inch weld-mesh and have half opening front lids and doors to allow easy access. Their floor substrate consists of forest bark and a bale of straw at the back covered by a waterproof roofing sheet to create an artificial banking. The voles will readily burrow into this feature, creating runs, nests and chambers. Swimming water is provided via a shallow garden seed tray at the front of the pen, which is changed daily in the summer. As breeding pens, these facilities work extremely well and groups of sibling litters have been over-wintered successfully in these enclosures.

The annual breeding regime consists of pairs of voles bred the previous year being introduced simultaneously to each other from February to March. Mates are selected to ensure relatively even weights and most females will produce a litter by mid May. Reproduction generally averages another three subsequent litters annually. Providing a stable food supply is maintained, water voles in these large family groups are very tolerant of each other, although occasionally odd individuals have to be removed due to aggression. These pens are checked for juveniles every three months and any early litter offspring are removed for release. Although both the straw bankings and floor substrates are replaced at this time, careful disturbance of nests of tiny, naked juveniles rarely results in casualties, as their parents will readily remove them by carrying them in their mouths to new nests. This high natural fidelity to their offspring is unusual in small mammals, but has been historically recorded in the wild (Paxman, 1994) and could be a behavioural adaptation to short term rises in water level. This rescue response has been recorded in other riparian rodent species such as the European beaver (Castor fiber) and male water voles have been recorded assisting females with this process (Ryder, 1962).

Adult females at the end of a single breeding season are commonly so physically exhausted from reproduction that despite additional feeding their body condition rapidly fades and they either die or lose the use of their hind limbs. Occasionally adult males in captivity will survive to mate again after a second winter but their breeding performance is generally poor. Having worked with approximately 15,000 animals to date for various reintroduction and translocation projects, we have never had a known age individual survive for over 2.5 years. The remaining adults and all sub-adults are wintered outside in family groups of around 7 individuals. Even if left together until well into a potential breeding season, reproduction amongst sibling groups is extremely unusual. By using these described methodologies, water voles can be captive bred by experienced individuals in significant numbers. In the long term it is clear that inbreeding is a significant problem for isolated populations. One study undertaken by Aberdeen University suggests that water voles will not willingly breed with individuals they are related to and that they can detect, for at least a period of 4 weeks, close relations by scent (Lambin, X. Personal communication). The reproductive rate of this species is extremely rapid and it is clear from review of various populations drawn from different sources that small isolated founder groups seldom breed as well as stocks drawn from large vigorous populations when subjected to the same regime of captive care. As a population becomes more inbred the incidence of white body markings becomes common and historically populations of completely cream animals have been recorded. (Strachan, R. Personal communication). Any large-scale recovery project for this species must therefore encompass the coordinated release of a series of genetically distinct vole populations, which have the future potential to interlink.

The first monitored reintroduction of water voles was trialled at the Barn Elms Wetlands Centre in 2001. This population is still in existence. Water voles are well distributed throughout the reserve itself and the population has expanded out from its initial location to occupy habitats on the Beverly Brook on the other side of the Thames. While this initial project is a clear success, it is less clear how durable it will prove in time as it is not linked to any other surrounding populations in the wider environment. Although we are theoretically aware that this could be an unviable prospect, there are examples from locations such as Teesside where completely isolated water vole populations, which exist in modest numbers in environments that are completely surrounded by urban or industrial landscape, have tangibly survived for many decades (Strachan, R. Personal communication).

Many of the reintroduction projects which followed Barn Elms failed and it really was not until 2003/4 that a different approach demonstrated any further potential. The development of the Chichester Coastal Plain sustainable farming partnership in 2000, between Oxford Universities WildCRU and other partner organisations, provided a tantalisingly intelligent example of what might be achieved (Strachan, R. and Holmes Ling, 2003). This remarkable venture saw a consortium of landowners combine to create, through agri-environment schemes, a 8,400ha project site within which the availability of water vole habitat trebled in a very few years through the restriction of livestock in riparian corridors by fencing, the creation of field margin junction ponds and the restoration of existing farm ponds. The project employed the highly effective “mink raft” system designed by the Game Conservancy Trust (Reynolds, 2003), to target, eliminate and re-monitor for the presence of this alien predator. By 2005/6 mink were extinct within the catchments project area and the relict population of water voles, which were believed to number around 100 individuals, were beginning to expand. In 2004/5 approximately 450 captive bred water voles were reintroduced to the central river systems, where mink predation had completely eliminated the species in the past, to genetically and numerically boost the indigenous populations. To date the sites’ character, whereby its water courses rise in the Southdowns without any other direct interconnectivity with external water bodies (other than the coast), has rendered mink recolonisation difficult and the water vole population as a result has expanded to reoccupy virtually all of the riparian habitat available within the former project area.

At the time of writing the DGC has participated in the production of over 15,000 animals for many translocation/reintroduction/supplementation projects in England, Scotland and Wales. These projects have followed a strategy of release site selection which has focused on catchment scale mink elimination in suitable landscape topographies. To date they have resulted in the development of a broad range of substantial free living populations of water voles which are drawn from captive bred individuals. Some of the largest, occupy footprints of approximately 20 square miles including main river systems, upland pools, former forestry drainage ditches and mires (the Trossachs water vole project, near Aberfoyle) while others have restored water voles to entire English river systems such as the River Meon (22 miles in linear extent in the Southdowns National Park). More ambitious projects still to reintroduce water voles to the whole of the Kielder Watershed in Northumbria are now underway in collaboration with Northumbria Wildlife Trust, Tyne Rivers Trust and the Forestry Commission. It is entirely likely that as our strategic understanding of mink eradication, based on new technologies and a better appreciation of their biologically limiting requirements is developed in ever greater detail, that so much more could be achieved.

This process of restoration has huge potential. We cannot afford to lose the water vole. Where it disappears as a species, so too does its ecological impact on river banks. Its impact on plant communities as a grazer and disperser of seeds disappears, as does its ability to provide a resilient, abundant prey resource. Although the attendant species which rely on its presence for all of the forgoing may no doubt stumble on for a time, even our currently crude understanding of ecology demonstrates quite clearly that unintended consequences are all too likely to follow. Will this result in their disappearance as well? While this is in fairness unpredictable, it is absolutely clear that it will not result in their benefit. We are not always as good as conservers of nature in Britain as we like to think we are. All too commonly when we have set historic targets for unrealistic recovery, we have simply moved the goal posts to ensure ‘success’ when their failure was self evident. In many landscapes where suitable water voles habitats still remain, no amount of wishful thinking, habitat creation or mink control will affect their ‘natural return’ across the artificial landscapes of environmental loss which now typify our ‘natural environments’. In others where tiny fractured populations still remain, then their augmentation with fresh, unrelated captive bred individuals will be essential for their medium term persistence. The two keys to successful water vole restoration are the availability of large-scale mosaics of sustainable wetland habitat and the effective long-term control of North American mink (Strachan, 1998). Both these criteria are obviously reliant on significant cooperative partnerships and all that is now required is the dogged persistence to established these on behalf of this robust species which is capable of incredible regeneration.

References:

• Blake, B. (1982). Reproduction in captive water voles. Journal of Zoology 1982. Mammal Society.
• Durrell, G. (1994). The Aye Aye and I. Harper Collins. Pages 159-163.
• Gow, D., Holder, K. and Jeffrey, C. (2004). Journal of the IEEM. In Practice No 44. Pages 14 – 17.
• Holder, K., and Jeffrey, C. (2004). Unpublished.
• Paxman, J. (1994). Fish, Fishing And the Meaning Of Life. Penguin books. Pages 33-34
• Reynolds, J.C., Short, M. J. & Leigh, R. J. Development of population control strategies for mink (Mustela vison), using floating rafts as monitors and trap sites. Submitted for publication.
• Ryder, S. (1962). Water Voles. The Sunday Times.
• Strachan, C., Strachan, R. & Jeffries, D.J. (2000). Preliminary report on the changes in the water vole population of Britain as shown by the national surveys of 1989-90 and 1996-98. The Vincent Wildlife Trust. London.
• Sratchan, R. and Holmes-ling, P. ( 2003). Restoring water Voles and Other Biodiversity to the Wider Countryside. Wildlife Conservation and Research Unit. Oxford University
• Strachan, R. & Jeffries, D.J. (1993). The water vole (Arvicola terrestris) in Britain 1989-90: its distribution and changing status. The Vincent Wildlife Trust. London.
• Strachan, R. and Moorhouse, T. (2006). The Water Vole Conservation Handbook . Second Edition. Wildlife Conservation Research Unit, University of Oxford, Tubney House, Abingdon Road, Tubney. OX13 5QL.
• Strachan, R., Moorhouse, T. and Gelling, M. (2011). The Water Vole Conservation Handbook . Third Edition. Wildlife Conservation Research Unit, University of Oxford, Tubney House, Abingdon Road, Tubney. OX13 5QL.
• Strachan, R. (1997). Water voles. Whittet Books. London.
• Strachan, R. (1998). Water Vole Conservation Handbook. Wildlife Conservation and Research Unit. Oxford University.
• Strachan, R (1999). The Mink and the Water vole. Analyses for Conservation. Wildlife Conservation and Research unit and the Environment Agency. Oxford University.
• Telfer, S., Piertney, S.B., Dallas, J.F., Stewart, W.A., Marshall, F., Gow, J., & Lambin, X. (2003) Parentage assignment reveals widespread and large-scale dispersal in water voles. Molecular Ecology, 12, 1939-951.

For more information about captive breeding projects, progress and policy see www.watervoles.com.

Header Image: Peter Trimming / Wikimedia Commons

About the Author: Derek Gow (Director of the Derek Gow Consultancy Ltd) founded the consultancy in 2003 having begun working with water voles in 1995.  Derek is a specialist in water vole mitigation and conservation projects, with over 25 years experience working with water voles, giving mitigation advice to developers and land owners and running a breeding program that has successfully reintroduced over 10,000 water voles across the UK. Derek is co-author of the Water Vole Conservation Handbook and has trained numerous individuals and members of other organisations on water vole handling, live trapping and restoration techniques. In addition, Derek is a key enthusiast and working group member for the reintroduction of the European beaver.