Impact of habitat destruction on water vole displacement for the purpose of development
The water vole (Arvicola amphibius) is one of Britain’s most endangered wild mammals. It is protected under wildlife conservation legislation in the UK and listed as a species of importance for the conservation of biodiversity in England, Scotland and Wales. Therefore water voles are an important consideration when planning applications are determined.
WildCRU has a long history of conducting research on water voles, investigating amongst other topics the causes of their decline and localised extinctions and specifically the impact of invasive American mink (Neovison vison) on their decline, reintroduction ecology, and health and welfare factors associated with reintroductions. This combined research has increased our understanding of water vole ecology and highlighted the means by which we can protect small, often fragmented populations. However, water voles are a single component of our biodiversity that must be considered alongside a myriad of factors when maintaining resources as part of, for example, the flood defence system, or when undertaking development work.
Guidelines outlined in the Water Vole Conservation Handbook (3rd ed.) currently suggest that habitat destruction over short linear distances along waterways where there is suitable water vole habitat in the wider environment is a suitable methodology which allows works to proceed. Throughout England and Wales, activities including ‘displacement’ of water voles by removing riparian vegetation to encourage them to move, has routinely been undertaken without the need of a license, relying on the ‘incidental result’ defence of potentially disturbing water voles when undertaking an otherwise lawful activity. This technique has been extensively used when undertaking maintenance work on ditches and waterways, and by Ecological Consultants working on development projects. To date there has been no rigorous study of the impact that such habitat destruction has on water voles. It is assumed that they will disperse out of the unsuitable habitat into adjacent habitat, but it is also possible that they adopt more fossorial habits or suffer increased predation from lack of cover.
A recent review on the interpretation of legislation pertaining to water voles by the relevant Statutory Nature Conservation Organisations (SNCOs), has included clarification of as to what constitutes an offence of the law, and what defences might apply. It is now considered that such activities are not covered by the ‘incidental result’ defence and therefore do, in fact, require a license. Depending upon the scope of the work operations in England may be carried out either under a Class License by a registered person, or under a site-specific licence. Works in Wales may only be conducted under a site-specific license.
A new Water Vole Mitigation Handbook (2016) has been recently published to promote best practise amongst ecological consultant undertaking water vole work, stipulating that further research is needed to test the effectiveness of the displacement method in relocating water voles. This project aims to fulfil that requirement by live-trapping and radio-collaring water voles in five distinct sites to establish their territories, before then undertaking vegetation removal over specific lengths of linear habitat, to investigate whether water vole do respond to such habitat manipulation and move. We will investigate the timescales involved with any such movement; the ‘optimal’ amount of vegetation removal and to what degree increased exposure might affect survival rates. This information will subsequently feed back into future mitigation guidelines for water voles.
Current guidelines can be found here: http://www.mammal.org.uk/sites/default/files/files/Water%20Vole%20Mitigation%20Guidance%20Final.pdf
Other WildCRU water vole projects:
Health and welfare in reintroductions; lessons from small mammals
The Upper Thames Water Vole Restoration Project