Epsilon Archive for Student Projects

Abstract

Semi-domesticated reindeer (Rangifer tarandus) husbandry in Sweden depends
largely on sustainable management and productivity of the herd. Herd
productivity is determined by the survival of the herd’s offspring from each
year, which is affected by factors such as weather conditions, forage abundancy
and predation. Predation of the reindeer calves by brown bears (Ursus arctos)
can become a significant limiting factor of the herd’s productivity. Previous
studies suggest the reindeer maternal condition to have an effect on calf
survival. Data from pregnant reindeer was collected through the years 2010 to
2016 in two Swedish reindeer herding communities with high predation rates
(Gällivare and Udtja) as part of a project investigating reindeer calf mortality
due to brown bear predation. Among other factors recorded, females were
weighed prior to calving and the presence of their calves on the summer and
autumn gatherings was recorded individually. Data on reindeer weight at precalving
was analysed in relation to calf survival. Ordinal regression was used to
describe the effect of weight by year and herding community over the
probability of calf mortality. Results showed a positive effect of female
reindeer’s weight at late pregnancy on the odds of survival of the calf until the
autumn. The magnitude of the effect of weight was lower than the fixed effect
of herding community. Differences in brown bear presence and year-to-year
variations can be highly influential on calf survival. The year 2011 was
predicted to have the lowest odds of survival, while the reindeer calves in
Gällivare community had an overall higher survival rate than the reindeer calves
in Udtja.