Index Line Catches as a Basis of Population Studies on Small Mammals

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Abstract
The studies were carried out in southern Sweden and dealt with factors affecting index line catches and the ratio between index line catches and population density. There is a pronounced repellent effect from trapped, sexually inactive animals in multiple catching traps when the catch approaches 1 animal per trap. During these conditions animals which become active soon after the traps are set will be over-represented. The catch is also influenced by the type of trap and bait used. In order to obtain unbiased samples there should be many single catching traps per trapping point. It was possible to transfer line values to population density by combined index line/removal captures. The relations between index line catch and population density were very different in the species Apodemus flavicollis. A. sylvaticus and Clethrionomys glareolus; the catch of the first one being proportionally greatest. There was no significant evidence of different trappability of the species during the year.