UBC Theses and Dissertations
Improving livetrapping methods for shrews (Sorex spp.) Stromgren, Eric Johnston
Known for their high metabolism, shrews possess an incessant need to eat high quality foods. This drives much of the biology of shrews and has caused great difficulties when attempting to study shrews using mark-recapture methods. I reviewed the literature and identified potential causes of varied trappability in small mammals. Weather related factors were important in determining activity levels and thus trappability. Social relationships (both inter- and intraspecific) were found to contribute to trappability, in some cases with dominant individuals completely excluding subordinates from traps. Trap type was the easiest factor for a researcher to vary, and thus received most of the attention in the published literature. Sherman, pitfall, and Longworth traps were commonly used, and although pitfall traps are commonly used as removal traps, there is the potential for their use as live traps. The pitfall and Longworth traps seemed the most appropriate for capture of particularly small mammals, especially shrews; however comparisons between these three trap types were confounded by differing methods used for each trap type, and small sample sizes. I tested the relative efficiencies of pitfall and Longworth traps for livetrapping vagrant shrews (Sorex vagrans), and found the Longworth trap to be much more efficient, capturing up to five times as many individual shrews as pitfall traps. I also tested the utility of addition of mealworms as food for shrews, and the effect of increased trap check frequency on the trap mortality rates of vagrant shrews. The addition of mealworms significantly reduced mortality rates, and the addition of one midday trap check, so that traps were not left open for more than 8 h, reduced overall trap mortality rates in mealworm baited traps from nearly 60% (in non mealworm baited traps, checked at 12 h intervals) to less than 10%. Finally, I tested the effect of drift-fences on capture rates of shrews in pitfall and Longworth live traps on riparian and upland traplines. I found no significant differences between the trap types, or between traps equipped with drift-fences, and those without. However, any effect would have been masked by overall low trap success during this experiment.
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