Influence of weasel (Mustela nivalis Linnaeus, 1766) odour on spatial behaviour of root voles (Microtus oeconomus Pallas, 1776)

Findings concerning the influence of the odour of the specialized predator Mustela nivalis Linnaeus, 1766, the weasel, on the behaviour of Arvicolidae (voles) suggested that there is an impact on voles' utilization of space. This question was addressed by studying the influence of weasels and their scent on the utilization of space by freeliving root voles, Microtus oeconomus Pallas, 1776. Eleven captured voles (6 males and 5 females) were selected for telemetric monitoring over 10 days. After the first 5 days a weasel in a cage was exposed, along with samples of its odour in the form of urine and faeces, at the determined "centre of activity" within the home range of these voles. The sizes of home ranges were compared between experimental and control voles and the former were found to be smaller than the latter following introduction of the predator. However the centres of activity did not shift, and the probabilities of individuals being encountered at them before and after were the same. To try to account for these reactions, a series of laboratory experiments with the same vole species (n = 50) was carried out to study the influence of weasel odour on locomotory activity and on distances from, and numbers of contacts with, the source of the odour. Voles recognized the predator's scent and responded with a level of locomotory activity that was lower, as well as by fewer contacts being made with the source, in the experimental group than in the control group. However, the distances kept from sources of predator odour were no greater than from control sources, and in fact, voles spent more time close to the source than at greater distances. The reaction of a root vole to the presence of a weasel in the home range is therefore not to escape from the range but to reduce the probability of an encounter with this predator by decreasing locomotory activity.