Reducing accidental shrew mortality associated with small-mammal livetrapping I: an inter- and intrastudy analysis

Shrews (Soricomorpha: Soricidae) are particularly vulnerable to mortality associated with small-mammal livetrapping. We compiled data on mortality rates and protocols from 16 different small-mammal studies and analyzed 16 years of livetrapping data from a single study in Algonquin Provincial Park, Ontario to assess factors affecting shrew mortality. In the comparison across studies, accidental mortality ranged from 10% to 93%. Mortality was lower in studies conducted in locations and at times of year with warmer average temperatures. We found no differences in mortality among bait and trap types across these 16 studies. In our intrastudy analysis from Algonquin Park, Sorex spp. experienced high mortality (81%) regardless of environmental conditions. In contrast, northern short-tailed shrews had low overall mortality (13%), but mortality increased on rainy nights and on colder nights when overnight temperatures dropped below 10 degrees C. Comparisons between 2 trapping protocols within Algonquin Park suggested that both Blarina brevicauda and Sorex sp. experienced higher mortality in Sherman compared with Longworth traps, but these effects were confounded by other differences in methodology between studies. Although we found evidence consistent with some shrew mortality being caused by caloric constraints, experimental studies on bait supplements are necessary to test whether providing high-calorie baits is an efficient method to reduce the widespread shrew mortality that occurs in small-mammal livetrapping studies.