Activity patterns of the common vole, Microtus arvalis ? Automatic recording of behaviour in an enclosure

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Abstract
The activity behaviour of the common vole, Microtus arvalis was studied in an enclosure during a one-year cycle. The number of voles varied between 2 and 25 specimens. Emergence from burrows, running through pathways and visits at a feeding site were automatically recorded by passage counters which we developed for use in the field. The results can be summarized as follows: 1. The voles were day-active throughout the year — no change of the activity phase was observed. A significant proportion of activity at daytime was due to foraging trips to the feeding site, but the voles were active in the pathway-system, too. At night only a few short visits to the feeding site were recorded and almost no activity in the pathways was detectable. 2. In addition to the day-activity recorded by the passage counters we observed other activities like burrowing and storage almost exclusively at daytime, especially at dawn and dusk. 3. During daylight hours the voles were active on the surface in a synchronized short-term activity rhythm of about two hours. 4. This clear-cut activity pattern was changed for two reasons only: by juveniles beginning to venture from their burrows and by wet and cold weather conditions. 5. The activity pattern of voles kept in a cage within the enclosure was in accordance with previous investigations — the caged voles exhibited a distinct short-term rhythm of feeding bouts during daylight hours and showed extensive wheel-running activity at night. Thus they had maximum locomotor activity at a time, during which the voles in the enclosure were only occasionally active on the surface. Including previous results we assume from our investigations that voles are primarily day-active organisms. Although the short-term rhythm is closely related to metabolic demands there is evidence that its basic function is not to forage but to emerge for regular control of the territory. The hypothesis is put forward that short-term activity on the surface, which is synchronized with the activity of the population, might be advantageous to maintain territories. In continuation it is suggested that specimen which defend their territories effectively are most likely to survive at high densities in population cycles. Therefore the complex temporal structure of the voles' activity pattern might be favoured by selection.