Evaluation of Pitfall Trapping in Northwestern Forests: Trap Arrays with Drift Fences

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Abstract
We operated pitfall arrays with 5-m drift fences at 30 stands in western Oregon and Washington for 180 days. Pitfall arrays had a pronounced removal effect on small mammals (but not on the herpetofauna) during the 1st 60 days of trapping. Conventional short (10-day) trapping periods were only adequate to detect the most common mammals. About 60 days were needed to compile a relatively complete species list (> 85% of species captured) at each site. Reptiles were caught almost exclusively in the summer; amphibian captures were correlated with increased precipitation in the fall. Short (2.5-m) drift fences were less effective than the standard length of 5 m. Funnel traps captured few forest vertebrates. Pitfalls captured more insectivorous mammals than did snap traps, but snap traps were more effective for a few cricetid rodents. Pitfall arrays are adaptable to many habitats and can help assess the presence of small vertebrates, such as shrews and amphibians, that are undersampled by other techniques.