The ecology of the water vole (Arvicola amphibius) in grassland habitats in the City of Glasgow

The water vole, Arvicola amphibius, is a declining British species. Its range is limited to riparian margins along water courses and reed beds and they are considered to have strict habitat preferences. Unusual populations living in grassland habitats in the East End of Glasgow came to light in 2008. This behaviour is largely unrecorded and poorly understood in British populations although grassland populations, termed fossorial, are common in some regions of Europe. The aim of this project was to update current surveying methodology which focuses on riparian habitat, map the distribution of grassland water vole populations in the East End and investigate habitat preference. An area of 34km² was surveyed using stratified sampling methodology and 100m presence/absence transects based on the identification of field signs. A total of 65 sites were identified; 65 were surveyed in March-April and 62 repeat-surveyed in Sept-Oct 2014. Of these 21 were occupied by water voles in March-April and 19 occupied in Sept-Oct. Water vole distribution was concentrated along a 3km stretch of the M8 corridor and adjacent grassland patches. Distribution of occupied sites was linearly related to distance from the M8 corridor with 62% of occupied sites less than 1km distant. Logistic regression modelling revealed that habitat type and distance from riparian habitat were key indicators in grassland water vole distribution. The distribution of water voles was not related to distance from riparian habitat: sites between 0-150m and sites over 550m distant had equal likelihood of occupation. Only sites at the intermediate distance of 151-550m were less likely to be occupied. Six out of the 9 breeding colonies recorded were over 550m from riparian habitat and at a maximum distance of 1182m. Water vole occupation was associated with urban habitats with parkland being the preferred habitat type over road verges and rank grassland. Parkland was characterised by heavy management regimes, moderate to high disturbance and low botanical diversity. The occurrence of water voles was strongly associated with certain grass species, particularly Holcus lanatus and H. mollis which were the dominant grasses on 43% of all occupied sites and 67% of breeding sites. Holcus grasses were also associated with the park habitat type. The main predators of East End populations were fox (Vulpes vulpes) and the domestic cat (Felis catus). American mink (Neovison vison) were never recorded. Trapping transects allowed for capture-mark-recapture at two sites and the estimation of population size by population modelling in Program MARK. Population densities were estimated at up to156 water voles per hectare indicating grasslands are valuable habitat for water voles. Their ecological distinctiveness and high densities provide strong evidence that the East End is a key regional stronghold for water voles and that the populations of Glasgow are of national significance. The need for an urgent re-think of current species management guidelines, mitigation protocols and standard surveying methodology has been highlighted by this research