Pellet Count Indices Compared to Mark–recapture Estimates for Evaluating Snowshoe Hare Density

Abstract

Snowshoe hares (Lepus americanus) undergo remarkable cycles and are the primary prey base of Canada lynx (Lynx canadensis), a carnivore recently listed as threatened in the contiguous United States. Efforts to evaluate hare densities using pellets have traditionally been based on regression equations developed in the Yukon, Canada. In western Montana, we evaluated whether or not local regression equations performed better than the most recent Yukon equation and assessed whether there was concordance between pellet‐based predictions and mark‐recapture density estimates of hares. We developed local Montana regression equations based on 224 data points consisting of mark‐recapture estimates and pellet counts, derived from 38 sites in 2 different areas sampled for 1 to 5 years using 2 different pellet plot shapes. We evaluated concordance between estimated density and predicted density based on pellet counts coupled with regression equations at 436 site‐area‐season combinations different from those used to develop the regression equations. At densities below 0.3 hares/ha, predicted density based on pellets tended to be greater than for mark‐recapture; the difference was usually <1 hare per ha on an absolute scale, but at low densities this translated to proportional differences of 1,000% or greater. At densities above 0.7 hares/ha, pellet regressions tended to predict lower density than mark‐recapture. Because local regression equations did not outperform the Yukon equation, we see little merit in further development of local regression equations unless a study is to be conducted in a formal double‐sampling framework. We recommend that widespread pellet sampling be used to identify areas with very low hare densities; subsequent surveys using mark‐recapture methodology can then focus on higher density areas where density inferences are more reliable.

Camouflage mismatch in seasonal coat color due to decreased snow duration

“…The area is temperate boreal coniferous forest comprising an array of uncut and harvested stands mostly on US Forest Service lands that are largely unpopulated. Hare densities in this region vary but tend to be less than two hares per ha (34). Snowshoe hares were livetrapped using Tomahawk traps (Tomahawk Live Trap Company, Tomahawk, WI) and fitted with radiocollars (Wildlife Materials, Murphysboro, IL) (17).…”

Modelling the Canada lynx and snowshoe hare population cycle: the role of specialist predators

“…Our model is the first to provide a quantitative match to cycle probes that include peak and low densities. Although low densities can be difficult to estimate accurately from field data (Mills et al 2005), all of the snowshoe hare density estimates were based on reliable mark-recapture live-trapping (Boulanger and Krebs 1996), thus providing high-quality information about this important phase of the cycle. Our model is the first to capture the very low minimum hare densities observed in the boreal forest near Kluane Lake (Hodges et al 1999).…”

Designing fecal pellet surveys for snowshoe hares

“…For rectangular plots, counts of uncleared plots were on average 1.1-fold higher than cleared plots, whereas for circles uncleared plots were 1.7-fold higher. Both cleared and uncleared plots were highly correlated with snowshoe hare density estimates from mark-recapture data (Mills et al, 2005;Hodges and Mills, unpublished data). People were not consistent at aging pellets of unknown age as >1-year-old or <1-year-old.…”

“…Mills et al (2005) found that pellet densities of 0.6 and 1.6 per small rectangular plot in western Montana were useful thresholds, as pellet densities <0.6 signified hare densities <0.3 hares/ha, while pellet densities of >1.6 indicated hare densities >0.7 hares/ha; in between, the relationship between hare density and pellet density was too variable for reliable inference about hare density.…”

“…Pellet counts are widely used for these questions relating to snowshoe hare abundances and habitat use because pellet counts have a relatively strong and repeatable relationship to markrecapture population estimates at different times, places, and hare densities (Krebs et al, 1987(Krebs et al, , 2001Murray et al, 2002;Mills et al, 2005;Homyack et al, 2006;McCann et al, 2008). Because different plot sizes and shapes produce different estimates of the mean and variance of pellet density (McKelvey et al, 2002;Murray et al, 2002), researchers using pellet counts to infer snowshoe hare abundance should use equations relating to the particular plot type they used.…”