The decline and local extinction of a population of water voles, Arvicola terrestris, in southern England

A colony of water voles occupying 1.6 km of the river Windrush (England) is described before it disappeared due to mink predation. Individuals were trapped every month for a week during 19 months. In addition, some individuals were radio-tracked in order to estimate their ranges and movement patterns. The numbers of latrines were counted seasonally and compared with the numbers of captured animals. The population reached a peak in July 1996 when 20 individuals were known to be alive indicating that the population was already very small. The number of individuals caught decreased in winter and new individuals appeared during the next spring although the population crashed in July 1997 due to mink predation. The sex ratio was similar to that reported elsewhere for British populations, but densities were lower than those reported elsewhere. Body size was smaller than previously recorded in the same catchment. Home ranges were significantly smaller in summer than in spring resembling situations of high and low densities respectively. Individuals showed restricted movements and no dispersal event was recorded. Available data seem to suggest that females form linear ranges that, though overlapping other juvenile females, exclude adult females. Males, on the other hand, have linear ranges that overlap several females and males.