Hair tubes for estimating site occupancy and activity-density of Sorex minutus

Hair tubes are efficient for sampling shrews and potentially important for sampling Sorex minutus, which is poorly sampled with other methods such as live trapping. We tested the effect of aperture size, bait, and position and type of sticky strip in hair tubes on the detection of S. minutus hairs. The optimum S. minutus hair tube design has high specificity for S. minutus (hairs are 12 times more likely to be from S. minutus than from other species), easily constructed and suitable for use in large-scale surveys. Between the end of July and middle of September 2008 we repeatedly surveyed 46 sites twice with a transect of 20 S. minutus hair tubes. Occupancy of S. minutus was higher in hedgerow sites (0.92) than grassland (0.59) and woodland sites (0.42). Relative activity-density was estimated from models allowing abundance-induced heterogeneity in detection probability and was also higher in hedgerow sites (1.75) than grassland (1.23) and woodland sites (0.72). Relative activity-density is a function of abundance and movement and hence should be interpreted with caution but is a valuable parameter to estimate from data on presence or absence of a species at a site. From our data we recommend that surveys are carried before the end of August, in which case three surveys per site at up to 120 sites per habitat (depending on habitat and start date) are necessary to obtain precise estimates of site occupancy. Site occupancy should be quantified as a relevant parameter alongside abundance when conducting indirect surveys of mammals and relative activity-density should also be considered.