Methodological aspects of the interval trapping method with comments on nocturnal activity patterns in house mice...

Activity periods in small rodents are influenced by a variety of factors including climatic conditions, photoperiod, resource availability, and competitors. The timing of nocturnal activity was examined in free-living house mice inhabiting large outdoor enclosures. Live-traps were checked at 2-h intervals on specified nights. Mice were more active just after dusk and less active just before dawn. There was no significant differential timing of activity by age or sex. Dominant males were more active in the latter half of the night and subordinate males were more active in the first half of the night. Questions pertaining to the availability of traps, the proportion of mice still not captured, density effects on capture rates, and human activity influencing mouse activity were also tested. On average, more than 86% of the traps remained open even for the 2-h interval nearest dawn. A minimum of 70% of the trappable mice were not captured on a given trap night. The rate of mouse captures did not increase with increasing density. There was no difference in the overall mean number of mice caught on nights with and without interval trapping. However, capture rates were significantly lower in the period after a 2-h trapping interval than in the periods before or during that interval. Adult males and adult non-reproductive females were caught again sooner if they spent more time in the trap. There was no effect of the amount of time spent in the trap on the time to recapture for adult reproductive females or male or female juveniles.