Scavenging and Predation Upon Sheep and Lambs in West Scotland

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(1) Foxes on two study areas, Ardnish and Drimnin in west Scotland, fed largely on sheep carrion and field voles, supplemented by deer carrion, rabbits and birds. They killed a minimum of 1.3, 1.8, 0.8 and 0.6% of the lambs estimated to have been born in 1976-79 respectively. (2) Foxes and eagles killed lambs mainly 1-5 days old and apparently in good condition. Foxes killed lambs as heavy as 10 kg, and eagles killed lambs up to 6 kg. (3) At Ardnish about 152 kg of carrion per km2 was available in 1976; at Drimnin 65 kg and 86 kg in 1977 and 1978. Assuming that they ate nothing else this could have sustained the resident foxes except in 1977 when foxes were numerous. (4) Sheep carcasses were more quickly scavenged in November-March and in July, when carrion was scarce, than in April-June when carrion was abundant and when much of it remained uneaten by vertebrate scavengers. (5) More carrion was eaten in the first half of the year, more field voles in the second. A vole peak occurred in 1977 and foxes ate substantially more voles in the autumn and winter of that year. Live prey was otherwise scarce. (6) Birds scavenged more lamb carcasses than foxes did except in 1977. Birds found difficulty in breaking into sheep carcasses (from which they usually removed only an eye and part of the tongue) prior to breaking by foxes and badgers. (7) More lambs were 1-10 days old and most vulnerable to predation in the first 10 days of May than at any other time in the lambing season. Lambs of sheep breeding for the first time may have been more vulnerable than those of older sheep owing to poorer maternal care.