An evaluation of vertically stratified traps for censusing small mammal populations

The use of vertically stratified traps for censusing small mammal populations in Loblolly Pine Plantation and Oak-Pine-Mixed Hardwood Forest was evaluated. Trap types and placements included: pitfalls, snap and live traps set in excavated burrows, and snap and live traps set at ground surface. Combinations used for two removal trapping methods were: (1) one pitfall and one snap trap set at ground surface per station, and (2) one snap trap set in a burrow and one at ground surface per station. Live traps were placed in the latter manner. Dominant species of small mammal communities in both habitats were Peromyscus leucopus, Ochrotomys nuttalli, Blarina carolinensis, and Sorex longirostris. Pitfalls did not appear effective for capturing P. leucopus and O. nuttalli, however, the design of this trap type herein may have allowed these rodents to escape capture, and interpretation was withheld. Neither of these species responded differently to snap and live traps set in burrows or at ground surface. In removal trapping, B. carolinensis was captured with greatest efficiency by pitfalls and snap traps set in burrows when each was paired with snap traps set at ground surface. Trap-revealed densities indicated that setting traps in burrows was the most effective method for capturing this species. This trend was also observed in live trapping. Higher numbers of S. longirostris were removed by pitfalls than by snap traps set in burrows or at ground surface. Response to the two placements of snap traps was variable and inconclusive while in live trapping distinctly more captures were made by traps set in burrows. The three methods of vertical trap stratification produced uniform rates of capture for the four cohabiting species. Highest initial captures were observed in live trapping with indication that complete capture of resident populations was accomplished during a five-day trapping session. Small mammals were taken at lower rates in removal trapping with no indication that resident populations were totally removed. This was attributed to a shorter adjustment period of two days used in removal trapping compared to a five-day adjustment period used in live trapping. Additional data were gathered on the distribution, density, standing crop biomass, diel activity, movement, home range, reproductive activity, and body measurements of the four common species.