The ecology of the water vole (Arvicola terrertris L.) in Southern England
Benge, Jonathan Mark
In the UK, the water vole is usually found associated with water; in rivers, canals, ditches, streams, lakes and ponds. Now listed as a UK Biodiversity Action Plan priority species for conservation it receives partial protection under UK legislation. The current study used various techniques to investigate aspects of the ecology of water voles at five sites in the southern England. Live-trapping techniques examined aspects of social organisation, such as population size, structure, distribution and Observed Range Lengths. Capture rates, weight differences and survival were also examined. Water voles became extinct from two study sites most likely due to American mink predation. Densities of water voles at three sites were generally higher than those recorded elsewhere, suggesting density may be dependent on type of habitat or other variables. Water voles were distributed along almost the entire length of these study sites. All populations peaked in size (as a result of juveniles entering the populations) and adult weights peaked in the spring and summer, declining in the autumn. Adult weights were generally lower than found in previous studies with no difference between adult male and female weights at any site. High rate of ear tag loss meant individuals could not be reliably followed between months, therefore the population estimates based on Minimum Number Alive (MNA) may have been significantly underestimated. The highest period of activity was between 22: 00hrs and 06: 00hrs corresponding with published studies. The relationship between water vole numbers and latrines was examined and compared with published literature. Seasonal patterns in the production of latrines were examined to gain further information on their function and the bearing that this may have upon any relationship between latrines and water vole numbers. Further examination considered the number of latrines per individual water vole and compared these with the published literature. Rainfall rendered many counts invalid as rising water levels or the act of the rain itself washed latrines away. Numbers of latrines per water vole were generally lower than published attributable to differences in the physical character of sites. Three sites showed a broadly similar trend in the numbers of latrine counts across months. Latrine numbers generally fell over winter which is likely to correspond with low water vole numbers and above ground activity. Peaks in latrine numbers in March and April were attributed to the onset of the breeding season whilst peaks seen in August were attributed to large population sizes. Relationships were found between latrines and the total number of water voles captured, MNA, adult females and all adults; latrines and adult females; all adults during the breeding season at two of the sites. The resultant predictive equation for the number of water voles from the number of latrines was not significantly different from the published relationship. Water voles were radio-tracked at one study site to examine overwinter behaviour. Home range sizes, movements, activity patterns and interactions were investigated. Due to time constraints and difficulty of intensive radio-tracking during cold conditions some sessions were done in August and September and some continued into March and April. Three of the tracked voles died during the study, two assumed to be through predation, probably by foxes, and one due to unknown causes. There was no difference between the area of male and female home ranges, however, male home ranges appeared to be longer than female ones. Increases in mean range length were seen in January, February and April likely to correspond to the onset of the breeding season. In many cases the majority of activity was centred on one or two points, identified as nest sites. A number of male water voles, and one female, dispersed to `new' home ranges. Activity occurred within discrete blocks of time, 1.5hrs to 4hrs with rest periods of 0.5hrs to 4.5hrs. Home ranges of a number of males and females overlapped and positive associations only occurred towards the end of the breeding season.