Relative Efficiency of Different Small Mammal Traps

Abstract

At some time in any study of small mammal populations the investigator is faced with the problem of whether the particular kind of trap used will adequately sample the population. It is common knowledge that exclusive use of one type of trap will tend to bias the estimate of population density due to varying amounts of selectivity in obtaining a population sample, since different types of traps vary in efficiency with respect to numbers, genera and species caught. Trap size and the correlated mechanical sensitivity of the trap also are obviously selective with respect to the size of specimen taken. An apparent avoidance of certain kinds of traps by some genera and species may involve odor, the appearance of the trap to the animal, or trap placement. However, certain anthropocentric concepts are involved here which are difficult to evaluate. Painting traps or camouflaging them in various ways have been used by some to overcome any real or assumed behavior of this sort without giving much quantitative evidence of success. Successful fur-trappers apparently employ these methods with considerable success to overcome reaction of the animal to the trap. There may also be individual variation in response to traps, as suggested by Young et al. (1952), Tanaka (1952, 1956) and Geis (1955), which would, if present, introduce a bias with respect to numbers of particular species trapped. The behavior of individuals and species is thus an important factor to consider in sampling any small mammal population. Although bait preferences (Fitch, 1954) may play an important part in seasonal trap response, they are probably of little importance in determining success of different trap types and use of the same bait in all traps compared at the same season would tend to nullify this factor. Cockrum (1947) found that live-trapping provided …