Can raptor predation limit or regulate grouse populations? II. Impact of predation on red grouse Lagopus lagopus scoticus
Thirgood, S.J. & Redpath, S.M. 1997: Can raptor predation limit or regulate grouse populations? II. Impact of predation on red grouse Lagopus lagopus scoticus. - Wildl. Biol. 3: 271.
Whether vertebrate predators can limit or regulate their prey has long been a controversial question in ecology. This study presents the findings of a 5-year study of predation by hen harriers Circus cyaneus and peregrine falcons Falco peregrinus on a red grouse Lagopus lagopus scoticus population in southern Scotland. Monitoring grouse numbers and productivity through counts with dogs, searching for grouse carcasses, and intensive radiotelemetry, combined with concurrent studies of raptor diet and breeding densities suggests that raptor predation may influence grouse populations in three ways. First, raptor predation during winter (October-March) may reduce adult grouse numbers by up to 50%. The extent to which this predation is compensated by other factors is currently unknown. Second, raptor predation in spring (April-May) may further reduce adult grouse numbers by an additional 30%. These losses are unlikely to be compensatory and, therefore, result in lost productivity. Finally, predation by hen harriers in summer (June-July) can result in up to 25% loss of grouse chicks produced by the remaining hens. The combined impact of spring and summer raptor predation can result in up to 47% reduction in productivity.
Key words: Circus cyaneus, compensatory mortality, Falco peregrinus, hen harrier, Lagopus lagopus scoticus, peregrine falcon, predation, productivity, red grouse, Scotland
Simon J. Thirgood, The Game Conservancy Trust, Crubenmore Lodge, Newtonmore, Inverness-shire, Scotland, PH20 1BE, United Kingdom
Stephen M. Redpath, Institute of Terrestrial Ecology, Monks Wood, Abbots Ripton, Huntingdon, Cambridgeshire, PE17 2LS, United Kingdom