A comparison of small mammal responses to clean and dirty traps.

Abstract

Most people studying small mammals are aware of the shortcomings involved in population estimates based on Longworth live-trapping. In particular, there has been much speculation on the effects of odours of a previous occupant on the trap-response of animals that may subsequently enter the trap, and the consequences of any such effects on the ensuing estimation of population parameters.

Rowe (1970) and Hurst & Berreen (1985) showed how trap-odour affected trappability of wild Mus domesticus and led to biased field data. Boonstra & Krebs (1976), working on Microtus townsendii and M. pennsylvanicus, Daly, Wilson & Behrends (1980) on Peromyscus, Montgomery (1979) on Apodemus sylvaticus, A. flavicollis and Clethrionomys glareolus, and Stoddart (1982a, b) on Microtus agrestis have all studied the effect of residual trap-odours on conspecifics. The effect varied both inter- and intra-specifically and inter-sexually and often conflicting conclusions have been drawn from studies of the same species.

Of the British species studied, Montgomery (1979) found that A. sylvaticus, A. flavicollis and C. glareolus all preferred traps that had previously caught conspecifics, although this result may have been due to spatial segregation in the rodent community rather than because of an odour effect per se. Stoddart (1982a, b), however, found that traps that had previously been occupied deterred subsequent M. agrestis individuals from entering. Stoddart therefore recommended that the Longworth traps should be washed, and cleansed of residual odours, before being used in a live-trapping programme.

This note describes an experiment, carried out as a pilot study to determine optimal trapping techniques, in which the effects of using 'clean' and 'dirty' Longworth traps were investigated.