A Survey of Water Vole (Arvicola Terrestris) Habitation of Coignafearn
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A survey of water vole ( Arvicola terrestris) habitation of Coignafearn Estate, Scotland Rebecca Priestley July 2011 Contents 1. Introduction………………………………………………………………………………..1 2. Study area………………………………………………………………………………….2 3. Method……………………………………………………………………………………..3 4. Results……………………………………………………………………………………..4 4.1. Evidence of water vole presence…………………………………………………….4 4.1.1. Burrow entrances………………………………………………………………4 4.1.2. Under-snow tunnelling………………………………………………………...4 4.1.3. Latrine sites…………………………………………………………………….5 4.1.4. Foraging………………………………………………………………………..6 4.1.5. Nests…………………………………………………………………………...6 4.1.6. Live sightings………………………………………………………………….6 4.1.7. Dead individuals……………………………………………………………….7 4.1.8. Tracks………………………………………………………………………….7 4.2. Distribution of water voles………………………………………………………8-10 4.2.1. Allt Fionndairnich…………………………………………………………….11 4.2.2. Allt Calder & Allt Odhar Mòr..........................................................................12 4.2.3. Allt Deamhaidh.................................................................................................13 4.2.4. Allt Coire Challich............................................................................................14 4.2.5. Allt Fionnach....................................................................................................15 4.2.6. Elrick Burn, Allt Glas a’Charbaid, Allt Glas a’Bheòil & Allt Glas a Chùil............................................................................................................16-17 4.2.7. Allt Creagach....................................................................................................18 4.2.8. Abhainn Crò Chlach....................................................................................19-20 4.2.9. River Eskin.......................................................................................................21 4.2.10. Other Burns......................................................................................................22 4.3. Habitat Characteristics..............................................................................................23 4.3.1. Slope………………………………………………………………………….23 4.3.2. Speed & type of water flow……………………………………………… 23-24 4.3.3. Vegetation…………………………………………………………………….24 4.3.4. Altitude……………………………………………………………………….25 4.4. Population size……………………………………………………………………..26 4.5. Evidence of predators……………………………………………………………...26 5. Conclusion………………………………………………………………………………..27 Acknowledgements…………………………………………………………………………..28 References……………………………………………………………………………………29 Appendices……………………………………………………………………………….30-35 1. Introduction The water vole (Arvicola terrestris ) has repeatedly been shown to be Britain’s most declining mammal ( Barreto et al 1998, Strachan et al 2000 ). The main threat is predation by invasive American mink ( Mustela vison ) (Lambin et al. 1998), but habitat degradation and fragmentation, together with corresponding population fragmentation and isolation have also contributed to its decline (WildCru 2004, Lambin et al 1998 ). Together these factors have resulted in an 88% decrease in just seven years, with some populations having declined by 98% (Strachan et al. 2000). Approximately 40% of the UK population is believed to occur in mainland Scotland, with a large proportion of these found in upland environments (Capreolus 2005). Although many sites in the Cairngorms and surrounding areas have been surveyed for water vole presence, Coignafearn Estate, in the centre of the Monadhliath Mountains, has not. Water vole ecology and habitat Water voles have a characteristic rounded body with a blunt muzzle and short rounded ears nearly hidden by the fur. Pelage is usually mid-red brown in colour, but upland individuals are frequently melanistic, turning the coat black (Strachan 1997). Adults weigh between 200 and 350g and measure approximately 29cm from nose to tail tip. They are normally exclusively vegetarian, consuming a mixture of sedges, rushes and grasses. Water voles create an extensive burrow system of tunnels linking food and nest chambers, with entrances both above and below water. Upland water vole populations are thought to exist as a series of metapopulations, which frequently undergo periods of localised extinction and new colonisation (Lawton et al. 1991). Prime habitat is densely vegetated with riparian plants including sedges, rushes, grasses and reeds. They tend to select slow-flowing water courses with earthy as opposed to rocky banks, and as such, ponds, streams and ditches make excellent habitat and may even be preferred to the main river channel (Strachan 1997). The water vole is a protected species and is listed under Schedule 5 of The Wildlife and Countryside Act. The UK Species Action Plan for the water vole requires conservation action to be directed to strongholds for the species and, consequently, areas believed to support water vole populations unaffected by mink should be of prime conservation interest. The objective of this study was therefore to survey Coignafearn Estate for water vole habitation and to map and document its distribution and characteristics. 1 2. Study area Coignafearn estate is located just outside the Cairngorms National Park, approximately 15.5 miles south of Inverness. It covers 39,606 acres and ranges from lowland riverine habitat to upland moorland up to 930m in altitude. The area is managed as a sporting estate for red grouse (Lagopus lagopus ) and red deer ( Cervus elaphus), with a strong emphasis on ecological restoration and the conservation of nature. It contains very few forested areas, with the dominant habitat type being upland peat moors vegetated by heather and grasses. Its main water course is the River Findhorn, which runs through the centre of the estate. This has nine main tributaries: Allt Fionndairnich, Allt Calder, Allt Deamhaidh, Allt Coire Challich, Allt Fionnach, Elrick Burn, Allt Creagach, Abhainn Crò Chlach and the River Eskin. Fieldwork was conducted from May 25 th - July 4th 2011. Figure 1: Location of Coignafearn Estate, 15.5 miles south of Inverness 2 3. Method A 1:25,000 Ordnance Survey map of the area was used to determine potential areas of suitable water vole habitat. These were defined as any water course that contained flattish areas. Steep burns were not predicted to support water vole colonies and, as this proved to be correct after an initial assessment, were not surveyed. Water courses were walked in their entirety and surveyed up to 9m on each side. Water voles were considered to be or to have been present wherever the following signs were observed: • Burrow entrances • Under-snow tunnelling • Latrine sites • Evidence of foraging (cropped grass or cut lengths of vegetation outside burrows) • Nests • Live sightings • Dead individuals • Tracks A Global Positioning System (GPS) receiver was used to mark the exact location of water vole presence. Wherever this was detected the following were recorded: • Number of burrow entrances • Slope (flat; slight; medium; steep) • Characteristics of watercourse (above/under ground) • Width and depth of watercourse • Speed of water flow (static; slow; medium; fast) Numerous burns were encountered that were not included on the O.S. map, but these were not surveyed due to time constraints. However any wet areas adjacent to mapped water courses were included in the survey. The River Findhorn itself was also not surveyed, although any marked side burns were included. Evidence of potential predators was also recorded: specifically mink ( Mustela vison ), otters (Lutra lutra ), stoats (Mustela erminea ) and weasels (Mustela nivalis ). Field signs comprised scats and tracks. 3 4. Results 4.1 Evidence of water vole presence 4.1.1 Burrow entrances These were the most commonly found signs of water vole presence. The number of burrow entrances found along the length of a single burn varied from 1 to over 600. The size of holes ranged from 4 to 8cm, with smaller holes often found alongside larger ones, presumably created by younger voles. Burrow entrances tend to be slightly wider than high and have no spoil heap outside. On occasion entrances were found as part of a clear (circular) colony but, most frequently, were in a linear arrangement extending along the course of a burn. Tunnels leading both into the open and into the water were encountered. Densely populated colony located to the side of a (medium-sized) water course… Figure 2: Water vole colony on a tributary of Allt Glas a’Chùil Figure 3: Burrow entrances extending in a linear arrangement along a tributary of Caochan nan Carnaichean Dubha 4.1.2. Under-snow tunnelling Evidence of under-snow tunnelling was found on 101 burns, at 53.2% of sites. This is part of the burrow system and clearly shows the movements of water voles during winter, when they may travel further from water due to the protection provided by deep snow. Figure 4: Under-snow tunnelling leading down into an underground pond on a tributary of Allt Coire nan Stri 4 4.1.3. Latrine sites Water vole droppings were found fairly infrequently, at only 36 sites (18.9% of total burns). 83 latrines were found altogether. The vast majority of these were at the water’s edge or outside a burrow entrance. Droppings are 8-12mm long and 4-5mm wide and are cylindrical with blunt ends. Those found ranged in colour from green when very fresh through to black, and brown when very old. The most latrines that were found at a single site was 9. Figure 5: Fresh droppings outside a burrow entrance on Caochan Chairn Lèith.