Influence of pitfall versus Longworth livetraps, bait addition, and drift fences on trap success and mortality of shrews

Pitfall trapping is believed to be the most efficient method for capturing shrews (Sorex spp.); however, Longworth live-traps have been used successfully in North America and Great Britain. Due to high metabolic rates, previous attempts to livetrap shrews have been faced with very high (exceeding 95 % in some circumstances) mortality rates. Here we report the results of two experiments attempting to integrate successful livetrapping of shrews into standard rodent trapping protocols. In Experiment 1 we compared efficiency of pitfall and Longworth live-traps operated with drift fences on 1-ha trapping grids for capturing vagrant shrews (Sorex vagrans) on agricultural set-asides in Delta, British Columbia, Canada. A total of 100 trap stations, on each of three trapping grids, were equipped with a 3-m-long drift fence and randomly assigned either one pitfall at the centre of each fence, or two Longworth traps, one at each end of the fence. In addition, we randomly selected 50 % of trap stations and provided 6 g of mealworms (Tenebrio molitor) larvae as bait. In response to high mortality rates, we varied the frequency of trap checks, with intervals of 12–14 h (long), 6–9 h (medium) and 3–4 h (short). Contrary to our predictions, Longworth traps captured significantly more shrews than pitfall traps. We observed the highest mean mortality rates in traps without mealworms, checked at long intervals. Shrews in mealworm-baited traps checked at short intervals experienced no mortality. Mortality rates in mealworm-baited traps checked at short and medium intervals were similar (t?=??1.33, P?=?0.20, Bonferroni-corrected alpha?=?0.004). In Experiment 2, we attempted to determine the relative gains in efficiency when using drift fences in conjunction with Longworth and pitfall traps. However, due to small sample size, we were unable to detect significant differences. A trapping protocol using Longworth traps in conjunction with drift fences, provided with mealworms as food, and checked at a maximum interval of 8 h should be sufficient to effectively include shrews in rodent livetrapping studies.