Effects of large carnivores, hunter harvest, and climate on the
mortality of moose calves in a partially migratory population
Abstract
Survival among juvenile ungulates is an important demographic trait
affecting population dynamics. In many systems, juvenile ungulates
experience mortality from large carnivores, hunter harvest and
climate-related factors. These mortality sources often shift in
importance both in space and time. While wolves (Canis lupus) predate on
moose (Alces alces) throughout all seasons, brown bear (Ursus arctos)
predation and human harvest happen primarily during early summer and
fall, respectively. Hence, understanding how the mortality of juvenile
moose is affected by predation, harvest and climate is crucial to
adaptively managing populations and deciding sustainable harvest rates.
We used data from 39 female moose in south-central Scandinavia to
investigate the mortality of 77 calves in summer/fall and winter/spring,
in relation to carnivore presence (defined as wolf presence and bear
density), summer productivity, secondary road density, winter severity
and migratory strategy (migratory versus resident) using logistic
regressions. Summer mortality varied significantly between years but was
not correlated to any of our covariates. In winter, calf mortality was
higher with deeper snow in areas with wolves compared to areas without
and increased more strongly with an increasing proportion of
clearcuts/young forests in the presence of wolves compared to when
wolves were absent. Lastly, increasing hunting risk was associated with
higher calf mortality, and migratory females had higher calf mortality
compared to stationary ones. Our study provides useful insight into
mortality rates of moose calves coexisting with two large carnivores and
with an intensive harvest pressure. Increasing our understanding of the
mechanisms driving calf mortality both in summer and winter will become
increasingly important if the populations of wolves and bears continue
to expand and the moose population declines, and both summers and
winters become warmer.