Effects of Trap Type on Small Mammal Richness, Diversity, and Mortality

Ryan B. Stephens and Eric M. Anderson

When evaluating richness and diversity of small mammal communities it is important to consider the impact that trap efficacy may have on these indices. The objectives of our study were to determine species specific trap efficacy relative to Sherman traps and pitfall traps, assess the impact of trap efficacy on measures of species richness and diversity, and compare mortality rates between trap types and if pitfall covers reduce trap mortality.

In the summers of 2009 and 2010, we trapped throughout Wisconsin in 5 vegetative communities. We used 180 transects (190 m-long) of 20 Sherman live traps spaced every 10 m and 10 pitfall traps spaced every 20 m for 4 consecutive nights. We trapped 3,261 small mammals of 23 species in 34,235 combined trap nights. Pitfall traps were more effective at capturing shrews and voles, whereas Sherman traps captured more mice (Peromyscus spp.) and squirrels. Irrespective of vegetative community, both trap types together captured significantly higher species richness and diversity than either trap type independently. Covers significantly reduced mortality of Peromyscus spp., but not for voles or shrews and covers reduced overall captures of voles.

Our results indicate that Sherman and pitfall traps capture different portions of the small mammal community and, regardless of the vegetative community, should be used in combination when assessing species richness and diversity.

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