Problems with Monitoring the Water Vole (Arvicola terrestris) in Warwickshire: Misidentification or Behaviour Change?

  • Marion Louise Arthur

    Student thesis: Master's ThesisMaster of Science by Research


    The Water Vole (Arvicola. terrestris) is the UK’s fastest declining mammal. Loss and degradation of suitable habitat and predation by other species, particularly the American Mink (Mustela vison), has decimated the UK population. Water Voles are now only present in isolated populations in the UK and their long term survival looks bleak. In Warwickshire, regular monitoring and surveying is undertaken to try and establish where populations are located. Owing to the voles’ intensely wary nature, this relies almost
    entirely on indirect identification of their presence using key field signs.

    However, field signs in the north of the county, are becoming misleading. Droppings of the right shape and consistency are being found, but smaller than would be expected. They are also being found during the winter months, when A. terrestris is known to spend most of its time underground. Latrines, another hallmark sign, are also absent in some places despite the identification of other key field signs. These factors may be resulting in false
    positives for A. terrestris presence in established locations. However, it is possible that they are actually representative of a genuine change in behaviour as noted by other researchers in an attempt to avoid predators such as Mink by hiding field signs, in particular latrines or changing their foraging behaviour.

    Research is needed to identify whether Arvicola terrestris is simply being misidentified in parts of Warwickshire or whether it may in fact have altered some aspects of its behaviour, particularly in response to predation. This is important in the generation of accurate records for the successful future conservation of the species.

    A series of surveys were carried out on three sites in Warwickshire to determine what species was leaving the field signs. After carrying out small mammal surveys it was found that the population of field vole was larger than any other small mammal species. Further research suggested that the field signs being found were very similar to those which are known to be field
    voles, and other publications reported the possibility of confusion

    Measurements of both water vole and the unknown species’ (likely to be field vole) feed remains and faeces showed a distinct difference in size. Water vole faeces measured 8 – 12mm while the likely field vole faeces measured 4 – 5.5mm. The water vole feed remains (published as measuring around 100cm) measured 46– 196mm and the likely field vole feed remains measuring 19–
    27mm. A 45 degree bite angle on feed remains is also published as being a sign of water vole presence, in this study 61 – 85% of the water vole field feed remains had a 45% bite mark, with the rest having a rough edge with no angled bite. In comparison, the 91 – 98% of the likely field vole feed remains had a 45 degree bite.

    The study suggests that the most likely cause for the possibly misleading field signs are that field voles are leaving them. On their own the 45 degree bite mark, feed stores and latrines may be misleading to an inexperienced surveyor and care should be taken not to be too quick to identify sites as water vole positive, particularly if the 45 degree bite angle is being used as a key indicator.
    Date of Award2008
    Original languageEnglish
    Awarding Institution
    • Coventry University

    Cite this