Estimating the cause and rate of mortality in red grouse Lagopus lagopus scoticus.

Abstract

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.