Efficiency of pitfalls versus live traps in enumeration of populations of Microtus pennsylvanicus

Two populations of Microtus pennsylvanicus were trapped simultaneously with longworth live traps and pitfall traps over a 3- and a 4-year period. The number of voles enumerated by live traps was usually between 2 and 4 times that enumerated by pitfalls. Of the 3671 new voles caught, 53.7% were first caught in live traps. Pitfalls captured more of the juveniles first (56%) and live traps captured more of the adults first (76%). Animals entering live traps for the first time were about 4 g heavier than those entering pitfalls for the first time. The time lag between entry first into pitfalls and then to live traps was 4-6 weeks; the time lag between entry first in live traps and then to pitfalls was 2-7 weeks. Approximately 18% of all voles never entered live traps. Live traps captured about 83% (N = 747) of all dispersers whereas pitfalls captured about 46%. We conclude that live traps were much more effective than pitfalls in capturing this species. These results are very different from those reported from studies on Microtus townsendii