Effects of plot size and shape on pellet density estimates for snowshoe hares

摘要

A variety of plot shapes and sizes have been used to estimate pellet densities of snowshoe hares (Lepus americanus), but we lack a clear understanding of whether plot shape and size affect measured pellet density. Snowshoe hare pellet densities associated with several plot designs were compared at 2 locations in the Rocky Mountains. Plot designs and pellet-inclusion rules were identical on both sites, but crews were independent. Density estimates were systematically biased by plot size and shape, with smaller plots and higher edge-to-area ratios leading to higher density estimates. In particular, the plot size and dimensions suggested by Krebs et al. (1987, 2001) produced the highest density estimates on both sites. Thus, we caution against using the regression equations developed by Krebs et al. (1987, 2001) if plot dimensions differ from theirs. Similarly, we believe that direct comparison of hare pellet densities (and; by inference, hares) between studies using different plot designs is not valid. Within the pellet density range associated with our study areas, we suggest using large circular plots except where comparison with other studies using Krebs et al.'s (1987, 2001) methodologies is vital. Large circular plots minimize potential inclusion bias associated with pellets on the plot boundary, are easy to implement, and are common in the literature.