DYNAMICS OF THE BURROW SYSTEM CONSTRUCTION OF THE FOSSORIAL FORM OF THE WATER VOLE (ARVICOLA-TERRESTRIS L) IN A VERTICAL TERRARIUM AND IN THE FIELD

Two kinds of experiments were carried out in order to study the construction dynamics of the burrow system of the water vole's fossorial form. a) animals released in the field b) animals kept in a terrarium (190 cm in length, 90 cm in height and 6 cm deep) In the first case, 2 couples were released in the field and studied over a period of 10 or 26 days. A map of the mounds was made on average twice a day. At the end of each experiment, the burrow system was excavated and mapped. The dynamics of the burrow development were reconstructed according to the position and emergence of mounds as a function of time. The following variables were evaluated for each observation: total length, number, surface area and volume of mounds, increments in burrow length, surface area and volume of mounds between 2 observations, number of vertices (= intersections and dead-ends), edges (= distances between 2 vertices) and the corresponding mean and standard deviation, as well as the increase of length, surface area and volume of the mounds as a function of time. Total length of the system, cumulated surface area and volume of the mounds over time, number of vertices and edges strongly correlated with each other and with time; surface area and volume differences correlated only with each other; mean and standard deviation of the edges correlated strongly with each other. The average increase in length of the studied burrow systems was about 80 and 170 cm/day, respectively. The mounds were modified quite frequently, due to newly excavated dirt pushed out of the burrow. In the second case, either a single individual (2 experiments), or a couple (2 experiments) was studied. A map of the burrow system was made on average every 1-3 days. The following variables were evaluated for each observation: total length and volume of the system, increments in length and volume between 2 observations, newly excavated volume and/or volume of refilled galleries, number of vertices, edges, elementary cycles, mean and standard deviation of the edges. Total length, volume, number of vertices and edges correlated with each other and with time; the length and volume differences correlated with each other, but not with the time interval between two observations; the mean and standard deviation of the edges usually correlated with each other. Total length, volume, number of vertices and edges correlated with each other and with time; the length and volume differences correlated with each other, but not with the time interval between two observations; the mean and standard deviation of the edges usually correlated with each other. A burrow system in a terrarium is longer when inhabited by a couple: x = 4.7 and 5.7 m vs. 3.1 and 3.4 m. The ratio of the standard deviation and the average length of the edges of a burrow system (= coefficient of variation), either in a terrarium or in the field is rather constant and usually close to 1.0 (0.66-1.2). The relationships between the different variables are analysed, interpreted and discussed.