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Résumé :
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[1. The object of the paper is to assess the importance of predation on red grouse numbers on two study areas in north-east Scotland, where we counted live grouse and found the bodies of nearly all those killed by predators. 2. The abundance of predators is expressed as the number of sight records per 100 h field work. 3. The main predators were fox and eagle on the hills at 700 m, and fox and hen-harrier at 300 m. At each level. foxes and raptors accounted for similar proportions of the total predation. 4. Maximum predation coincided with the seasons when grouse dispersed and with the numbers of grouse dispersing. Resident territorial grouse were relatively invulnerable to predation compared with surplus birds without territories. Predation mortality was not density dependent, but was probably proportional to the numbers of surplus birds. 5. Changes in the frequency of birds of prey on the moors were correlated with annual variations in the numbers of grouse dispersing. Factors influencing other predators are discussed briefly. 6. We conclude that the frequency of visits by predators to this habitat was partly determined by the availability of dispersing grouse as prey and partly by other factors that are not understood. Except locally and seasonally, gamekeepers did not seem to depress the numbers of predators, and predation was not important in limiting either the numbers of breeding grouse or the numbers available subsequently for shooting.]
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