Mortality in Svalbard reindeer

Mortality rates in Svalbard reindeer followed the "U"-shaped pattern, with higher mortality rate among calves and old animals than in middle aged individuals. Assuming a stable population size, the mortality data predict a 16.2% annual mortality and recruitment rate among 6 months and older animals, and a male:female sex ratio of 48.5:51.5 among 1-yr old and older. Both predictions are supported by field data. Female mortality rate increased and differed from the male rate in the age interval 2-4 yr, while the male rate increased sharply and differed permanently from the female rate in the age interval above 6 yr. First and last breeding are thought to cause the increased mortality among 2–4 and 11–13 yr-old females. Increased involvement in rutting activities with age associated with lower grazing activity and depletion of fat reserves probably cause the increasing mortality rate among the 6+ yr males. Maximum life span was 17 yr in females and 12 yr in males. Apart from the unknown but possibly high neonatal calf-mortality, only few animals died during summer or during the rut in autumn. Death among calves, yearlings and most of the females occurred before antler-shedding in May-June. Most of the 2-yr and older males died after antler shedding, which occurs from December among the oldest and during April-May among the younger males. Hence, the major part of the mortality takes place in spring. The lack of visible subcutaneous and femur fat in most carcasses indicated starvation as the major mortality cause.