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NATURE AND ENVIRONMENT
The Distribution of the Water
Vole in Caithness
Future Work - Acknowledgments - References
Now that a baseline distribution of the water vole in the Caithness area has been established, it is important to continue to monitor those areas surveyed and also to build on this work. Ecological theory states that the rate of dispersal between populations is influenced by the distance between neighbouring populations and suitable habitat and therefore also encouraging recolonisation of areas of suitable habitat (1). Hence the closer an area is to the population network, the greater the chance of a positive survey result. For this reason, it makes sense to form subsequent survey plans radiating from this baseline distribution. Since the highest populations appear to be in the Latheronwheel area, further effort should focus on surveying burns toward the west of this area, where it is expected that there will be further suitable habitat and occupied sites to be found.
The results indicate that the water vole population is likely to extend throughout the Caithness peatlands although, in accordance with the metapopulation paradigm, not all suitable sites will be continuously occupied. Sites will be highly dynamic through the years and whilst a population may go extinct for any number of reasons in one area, another patch may be recolonised, thus maintaining the collective population. Monitoring of both occupied and unoccupied areas is therefore crucial to the future of this project. Additionally it will be important to conserve as large an area as possible since degradation of habitat, even if it is unoccupied, could threaten the persistence of the metapopulation (4).
The site of Munsary Peatlands was selected as a survey location because it was representative of dubh lochs, a typical habitat of Caithness. The survey was concentrated on the rivers and streams surrounding the dubh lochs, such as Munsary Burn and Allt-nan-Scaraig, as habitat appeared most typical here, and subsequently showed signs of occupancy. The area of Munsary Dubh Lochs was also surveyed but no signs were found in the bog pools. However, water voles can inhabit bog pools, particularly if there are tussocks of moss or grass that are both suitable for burrowing and high enough above the water level to minimise flooding of burrow systems (11). It is therefore suggested that a more detailed survey of the actual bog pool system at Munsary is carried out, as well as surveys of other dubh loch systems such as Dubh Lochs of Sheilton.
In addition to the suggestion of actual sites to survey, it is also recommended that future surveying takes place in spring/summer, prior to extensive vegetation growth. In terms of ease of surveying, priority should be given to those sites described as ‘poor’ since these sites were the most overgrown. Surveyors should also be aware of any signs of predators, in particular American mink.
A high level of vigilance will be required to observe movement of mink into the county. Landowners and gamekeepers will be particularly instrumental in monitoring any invasion of mink. Techniques to detect the spread of mink (using mink rafts developed by the Game Conservancy Trust) have been used successfully in Aberdeenshire (12) and have recently been deployed in the River Broom, Wester Ross, by the Scottish Wildlife Trust (13). These techniques could easily be transferred to Caithness but the support of landowners and gamekeepers would, of course, be essential.. A system for reporting mink sightings or other evidence of their presence is required. Measures to control mink should be prepared and be ready to implement quickly in the event of mink incursion.
This project is part of the Highland BAP Implementation Programme, financed by the European Union under the North and West Highland Leader+ 2000-2006 Programmes, Scottish Natural Heritage and The Highland Council.