Body condition and ranging behaviour of blackface hill sheep in relation to lamb survival.
Factors affecting the production and survival of lambs, including vulnerability to predation, were studied in a flock of about 850 Blackface hill sheep in Argyll, West Scotland. The poorer production of lambs by gimmers (sheep breeding for the first time), was not due to a lower pregnancy rate or to poorer body condition, but may have been affected by poorer maternal care. Lambing reached a peak between 4 and 10 May. Sheep withdrew from the flock to lamb and returned within 1-3 days. If the distance between sheep and their lambs is regarded as a measure of vulnerability to predation, then lambs of ewes were less vulnerable than those of gimmers. Sheep moved uphill at night, but less so in June than in February-March. The numbers of sheep within a circle of 50 m estimated diameter increased between afternoon and evening. The anti-predator value of this behaviour is discussed. Home ranges in the lambing period varied from 33 to 55 ha, with a mean of 44.4 plus or minus 1.7. These were larger than in other studies of hill sheep in Scotland.