Thirgood, S.J, Redpath, S.M., Hudson, P.J. & Donnelly, E. 1998: Estimating the cause and rate of mortality in red grouse Lagopus lagopus scoticus. -Wildl. Biol. 4: 65-71.
We assessed biases in the techniques used to investigate the cause and rate of mortality in two red grouse Lagopus lagopus scoticus populations in Scotland during 1985-96. Comparison of the field signs left on grouse carcasses by known predators suggested that whilst it was usually possible to distinguish between grouse killed by mammals and by raptors, it was not possible in most cases to further distinguish between grouse killed by peregrine falcons Falco peregrinus and hen harriers Circus cyaneus. Similar estimates of the cause and rate of grouse mortality were derived from systematically counting grouse and searching for carcasses and by radio-tagging. Searching for carcasses may provide a useful technique for identifying major causes of mortality in grouse populations inhabiting open habitats.
Key words: carcass searching, field signs, Lagopus lagopus scoticus, mammals, mortality, radio-tagging, raptors, red grouse
Simon J. Thirgood & Eric Donnelly, Upland Research Group, Game Conservancy Trust, crubenmore Lodge, Newtonmore, Inverness-shire, PH20 1BE, UK - e-mail: sthirgood@compuserve.com
Stephen M. Redpath, Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire, PE17 2LS, UK
Peter J. Hudson, Department of Biological and Molecular Sciences, University of Stirling, Stirling, FK9 4LA, UK
Received 25 February 1997, accepted 9 October 1997
Associate Editor: Kjell-Einar Erikstad