Mechanical Time-Sorting of Pitfall Captures

Abstract

(With 1 Figure in the Text) During an investigation of the diurnal activity of the fauna of the floor in two contrasted habitats, preliminary estimates were made by counting, at regular intervals throughout the day, the number of animals seen to move in small quadrats. The limitations of this method soon became obvious. The weather was found to exert a controlling effect on the number of active invertebrates so that it was imperative, if valid comparisons were to be made, that the two habitats be sampled simultaneously. Further, critical scrutiny of small quadrats could only be maintained for about eight hours, even with rest pauses between observations, so that three periods of observation were needed to build up a single cycle of twenty-four hours. Allowing appropriate hours for sleep, this meant that four or five days were spent on each cycle, and during that period marked changes in the weather could occur and confuse the picture even within a single habitat. A method was required which would allow simultaneous sampling of two areas and also give continuous sampling through a 24-hour period. The pitfall trap, long used by coleopterists, suggested itself as the best method of sampling the running fauna, with some mechanism for separating the catch into definite periods. The apparatus described below was designed to meet these requirements and may prove of use to other field workers in conditions where the sorting mechanisms described by Williams (1935) and Johnson (1950) are not suitable.