Abstract
Survival of juvenile ungulates represents an important demographic
parameter that influences population dynamics within ecosystems. In many
ecological systems, the mortality of juvenile ungulates is influenced by
various factors, including predation by large carnivores, human hunting
activities, and climate-related variables. The relative importance of
these mortality sources often exhibits spatial and temporal variation.
While wolves (Canis lupus ) are known to predate on moose
(Alces alces ) throughout all seasons, brown bears (Ursus
arctos ) primarily engage in predation during early summer, while human
harvest activities primarily occur in autumn and early winter. Hence,
understanding the impacts of predation, harvest, and climate on the
survival of juvenile moose is crucial for adaptive population management
and the determination of sustainable harvest rates.
To investigate the summer and autumn-winter survival of moose calves in
relation to carnivore occurrence (wolf presence and bear density),
summer habitat productivity, winter severity, human harvest, and
migratory strategy (migratory versus resident), we analysed data
collected from 39 GPS-collared female moose in south-central
Scandinavia. Cox proportional hazard models were used to examine the
dataset, which included 77 observations of calf survival.
Our findings revealed significant interannual variation in summer
survival rates, which were negatively correlated with bear density.
Specifically, areas with high bear density exhibited calf mortality
rates twice as high as those in regions with low bear density. During
the autumn-winter period, calf survival was lowest in the presence of
wolves and deep snow, and it exhibited a negative correlation with the
proportion of clearcuts and young forests within the mother’s home
range. Additionally, calf survival was negatively correlated with the
risk of human hunting, and calves of stationary females displayed ten
times higher survival rates compared to migratory individuals.
Our study provides valuable insights into the survival of moose calves
coexisting with two large carnivores and humans. As wolf and bear
populations continue to expand alongside declining moose populations,
intensifying hunting pressure, and the potential threat of warming
summers and winters, improving our understanding of the underlying
mechanisms driving calf survival during both summer and winter seasons
assumes increasing importance.