Evaluating the efficiency of pitfall traps for sampling small mammals in the neotropics

Using standardized small mammal surveys at 26 Atlantic Forest sites, we evaluated the efficiency and compared the weight of captured species and individuals between large pitfall traps and Sherman traps. We also investigated the effects of climatic variables on daily capture success of pitfalls. Pitfalls were clearly more efficient than Sherman traps, capturing 29 species, of which 16 were captured exclusively with this method-mostly represented by rare species. In contrast, Sherman traps captured 14 species, of which just I was not captured with pitfall traps. Compared to Sherman traps, pitfalls captured (per site) 3 times the number of species, 2 times the number of individuals, and significantly more individuals of 7 species. Despite differences in sampling efficiency, positive correlations suggest that at least coarse-scale variation among sites for several assemblage parameters are congruent between the 2 trapping methods. Sherman traps tended to capture adults, whereas pitfalls captured individuals over a broader range of weight classes or tended to capture more juveniles. Total daily capture rates in pitfall traps increased with precipitation. Our results suggest that large pitfall traps are effective at capturing rare species and juveniles, probably because they are less selective, and are thus essential for inventorying the rich and poorly known small mammal fauna of the tropics and for demographic studies.