Can distance sampling and dung plots be used to assess the density of mountain hare Lepus timidus?

Abstract

We evaluated distance sampling and dung plots as cost-effective methods of estimating the density of mountain hares Lepus timidus on moorland in the Scottish Highlands. We compared density estimates derived from these techniques to those derived from labour-intensive capture-recapture techniques. Distance sampling and capture-recapture techniques produced comparable density estimates at medium and low hare densities. Density estimates derived from distance sampling were higher than those derived from capture-recapture in high-density hare populations. Both distance sampling and capture-recapture techniques gave wide confidence intervals at high hare density. Histograms of perpendicular sighting distances showed that a large proportion of hares were seen on or close to the transect line and that there was a rapid fall off in detection rates with distance. This finding indicated that hare behaviour may lead to problematic survey design and may reduce the precision of density estimates. The collection of accurate distance sampling data was particularly problematic when hare density was high. In contrast, in low-density hare populations, considerable sampling effort was required to obtain sufficient sightings of hares to reliably estimate density. Dung plots provided a relative index of abundance that successfully ranked populations of mountain hares in order of increasing density as determined by distance sampling and capture-recapture techniques. With careful study design, distance sampling provides a good compromise between accuracy, precision and effort in estimating the density of mountain hares. The use of dung plots is a rapid alternative when only estimates of relative abundance are required.