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.