Odor as a Component of Trap Entry Behavior in Small Rodents

Abstract

For many years students of small rodent ecology have utilized live-traps and capture-mark-release techniques for examining basic population parameters. In a great majority of studies, estimates of population size, and related parameters such as density, sex and age distribution, are based on one of a number of derivatives of Petersen’s index, all of which demand traps to have an equal sampling efficiency. Since a trap remains passive, and effects capture only after a rodent has purposely entered it, it cannot be used to sample a population of rodents in the same way that, for example, a drift net will sample a population of pelagic fish. Rodents do not blunder into live traps (although a few studies have employed pitfall traps) — they will only be caught if they can overcome any inhibition which they show towards the trap (Shillíto 1963). Although phenomena such as “trap-shyness” and “trap-proneness” have long been recognized, (in which certain individuals are caught less or more frequently than would be expected by chance if the traps were sampling the population randomly (Chitty and Kempson 1949)), it is surprising that so little attention has been paid to whether the ability of a given trap to catch a given individual is influenced by residues left behind by a previous occupant. If residues do influence the subsequent pattern of trap entry, estimates and analyses will be inaccurate and distorted by an unknown amount.