Estimation of rodent numbers by means of prebaiting and intensive removal

Abstract

The aim of investigations was to elaborate an accurate and labour-saving method of estimating the numbers of small rodents. Each of 8 two-week series of captures consisted of: (1)aseven-day period of prebaiting the rodents on an area of 5.76ha, over which a grid of 256 points with bait was arranged and (2)aseven-day period of intensive removal of rodents by means of snap-traps, two of which were set on each point. No correlation was found between the number of baits consumed and the number of rodents on a given point. From 78-100 per cent of all rodents captured over a seven-day period were removed by the fifth day. Differences were found in the rate of removal of different species of rodents and of marked and unmarked individuals of the same species. Estimate of population numbers was made by the regression method, obtaining satisfactory results in 17 cases out of 18 possible. This method is recommended, but it is suggested that the prebaiting and removal periods should be shortened to five days each.