Spacing pattern and mating system in water voles (Arvicola terrestris) in north-east Scotland
This study is focused on the population ecology of water voles (Arvicola terrestris) in linear habitats in north-east Scotland. The three aims of this study were (a) to assess one ecological method for estimating population size, (b) to identify ecological factors acting on individual spacing patterns, and (c) to make and test predictions about the mating system based on the observed spacing pattern. Data from latrine counts were used to validate a method previously proposed to estimate the population size of water voles. The relationship between latrine counts and vole abundance from sites with a broad range of population size was used in the calibration, and equations were derived from six different regressions with appropriate confidence limits. Due to the uncertainties involved, the calibration appeared to be unreliable for estimating the true population size. Two hypotheses, food-defence and pup-defence, previously proposed to explain territoriality of adult female microtines, were tested experimentally by manipulation of food during the reproductive cycles. Female home range length and daily distance moved were monitored by radio-tracking. The changes observed in home range length, movement, and distance between neighbours, suggested that both food-defence and pup-defence influence the spatio-temporal pattern of territoriality in female water voles. Spacing patterns of adult males and females, and the movement of males in relation to oestrus females, were studied by radio-tracking. A male removal experiment was also conducted to establish the method of home range marking by males. The study showed that intersexual overlap was more pronounced than intrasexual overlap, with males showing more intrasexual overlap. Male with heavier weight and larger distances moved were able to monopolise large numbers of receptive females. Results from the male removal experiment suggested that home range boundaries of males were not maintained by daily contact between neighbours. The pattern of space use by both sexes, and the timing of oestrus in females, predicted that mating system is promiscuity.