Estimating low-density snowshoe hare populations using fecal pellet counts

Abstract

Snowshoe hare (Lepus americanus) populations found at high densities can be estimated using fecal pellet densities on rectangular plots, but this method has yet to be evaluated for low-density populations. We further tested the use of fecal pellet plots for estimating hare populations by correlating pellet densities with estimated hare numbers on 12 intensive study areas in Idaho; pellet counts from extensive transects (n = 615) across northern Idaho enabled rectangular plots (0.155 m2) to be compared with paired small (0.155 m2) and large (1 m2) circular plots (metre-circle plots). Metre-circle plots had higher pellet prevalence, lower sample variance, and lower estimates of pellet density than the other plot types. Transects comprising circular plots required less establishment time, and observer training reduced the pellet-count bias attributable to plot shape. The number of hares occupying intensive study sites was correlated with pellet density on all plot types, but rectangular plots provided a slightly closer linear fit to hare numbers than did metre-circle plots. The relationship between pellet density and hare number may have been curvilinear rather than linear, but linear and nonlinear models provided similar numerical estimates over much of the range of pellet densities. These results indicate that pellet counts are a robust estimator of hare numbers in low-density populations, and that metre-circle plots represent an improvement over standard rectangular plots in terms of unbiased pellet counts, sacrificing little predictive power. We recommend using pellet counts in metre-circle plots for estimating populations of snowshoe hares in their southern distribution.

The effects of clearcutting on snowshoe hare (Lepus americanus) relative abundance in central Labrador

“…Each plot consisted of five, 1 m 2 circular subplots: one central and the remaining four in the cardinal directions 10 m from the center point. We used pellet counts in each subplot as an index of hare relative abundance (Murray et al, 2002). Pellets were classified new or old according to Krebs et al (1987).…”

An appraisal of the fitness consequences of forest disturbance for wildlife using habitat selection theory

“…Pellet plots were equidistantly spaced by 75 m (i.e., equilateral triangles with 75 m per side) such that each pellet grid covered an area of 6 ha. The average minimum distance between the edges of pellet grids in adjacent habitats was 145 m. We used large circular pellet plots with a 1.5-m radius (area = 7.07 m 2 / plot), to increase the probability of encountering pellets within plots under low hare density (Murray et al 2002). Pellets were cleared from all plots in summer 2006, and new pellets were counted and cleared in the summers of 2007 and 2008, except for four grids (one CPPTM and one CPRS cut paired with uncut stands) that we installed in the summer of 2007.…”

“…We used the mean density of pellets (calculated as pellets/m 2 ) in each habitat (average of 19 plots/habitat) as an index of relative snowshoe hare abundance as a strong link has been made between pellet density and hare abundance across several regions (Krebs et al 2001b;Murray et al 2002;McCann et al 2008). Pellet counts from both years varied between 0 and 130 pellets/plot.…”

Towards a standardized index of European rabbit abundance in Iberian Mediterranean habitats

“…This method is time consuming and labor intensive and it is necessary to optimize the time of visits (Massei et al 1998). This method can provide reliable estimates of abundance when animal densities are low (Murray et al 2002), a situation limiting the accuracy of other methods. Other signs, such as scrapes and tracks, are rarely used to obtain indices of rabbit abundance (but see Twigg et al 2001).…”