Evaluation of the distance sampling technique to survey red grouse Lagopus lagopus scoticus on moors in northern England.

Abstract

We surveyed red grouse Lagopus lagopus scoticus using pointing dogs in spring and again in summer from 2000 to 2010 on four moors in northern England using a line-transect distance sampling method. We compared density estimates generated with those obtained using three other methods on the same moors: counts of calling males within sample blocks of 0.5-km², absolute counts of grouse within sample blocks of 0.5-km² using a line of beaters and gamekeepers' own transect counts obtained using their dogs. We found that distance estimates were positively correlated with abundance estimates from all three sampling methods. Our distance sampling estimates of males pre-breeding were 47% higher than call count estimates, with pre-breeding distance sampling estimates 65% higher than the absolute counts. Distance sampling along transects across the whole moor provides a method for extensive surveys of red grouse, generating estimates of grouse population size at a moor level which can be directly related to management practices, particularly to harvesting and parasite control strategies.