The Activity of Free-Ranging Wood Mice Apodemus sylvaticus

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Abstract
The presence or absence at the nest of 14 radio-tagged A. sylvaticus (L.) was automatically monitored in the wild. Each mouse was monitored for between 7 and 14 days. In midwinter each of the 2 males and 2 females monitored showed a very varied pattern of nocturnal activity, each usually having between 3 and 5 outings from the nest each night, but with little synchrony in outing times between nights. A short-term rhythm was exhibited by 2 mice, and possibly another, the modal durations of time spent in the nest between outings being 1.5-2.0 h and 3.0-3.5 h. In spring each of the 2 males and 2 females monitored showed a strongly bimodal pattern of activity, with peaks of activity at 2-4 h after sunset and 3.5-4.5 h before sunrise. Generally each mouse had 2 major outings each night, each lasting about 2 h, and 1 or more minor ones for 1 h or less. In summer each of the 3 males and 3 females monitored showed a unimodal pattern of nocturnal activity. The mice rarely returned to their nests between their exit at dusk and their return at dawn. Two breeding females monitored in June and July both also left their nests for 2-4 h in the middle of the day, in addition to their nocturnal activity. Time of 1st emergence from the nest each night was strongly correlated with time of sunset, but time of last return was not correlated with sunrise. The total amount of time spent out of the nest each night increased from winter to summer. In winter, time spent out of the nest each night increased with both increasing ambient temperature and with decreasing moonlight. Below about 2.degree.-4.degree. C temperature is more important; above 2.degree.-4.degree. C moonlight is more important.