Mortality of lambs in free-ranging domestic sheep (Ovis aries) in northernNorway

Domestic lamb mortality on an open forested and alpine summer range in the municipality of Malselv in northern Norway was investigated. Two hundred an d fifty-three lambs in four of the area's six flocks were randomly fitted w ith mortality transmitters and monitored throughout the summer grazing seas on from June to September. Total losses in the six flocks were 183 (22.9%) lambs and 20 (4.2%) ewes. The carcasses of 69 lambs, 36 of which had radio- collars, and six ewes were recovered. Of the collared lambs, eight (22%) di ed as a result of disease and 27 (75%) were killed by predators. Implicated predators included red fox Vulpes vulpes, lynx Lynx lynx, golden eagle Aqu ila chryisaetos and wolverine Gulo gulo. Diseased animals included those di agnosed with pasteurellosis, disrupted intestinal functions and advanced co ccidiosis. The remains of one lamb were too decomposed for necropsy, though there was no evidence that it had been attacked by a predator. Factors ass ociated with losses were identified using logistic regression. Age of lamb at time of release on the summer range and age of dam were statistically as sociated with lamb losses (P < 0.05). Mortality was higher among older lamb s and those of year-old ewes. Parameters commonly associated with lamb size and growth were not statistically associated with mortality. The negative association between lamb mortality and age of dam may be related to the qua lity of maternal care provided by ewes of different ages, particularly vigi lance in the habitat of predators. Similarly, the positive association betw een mortality and age of lamb may be related to changing lamb behaviour, sp ecifically increased distance from ewe, as lambs grow older and more indepe ndent. Predators, when present, are a major cause of mortality in free-rang ing lambs, as in most wild ungulates.