Acceleration data reveal behavioural responses to hunting risk in Scandinavian brown bears

Predation may indirectly influence prey’s fitness and population dynamics
through behavioural adjustments in response to perceived predation risk.
These non-consumptive effects of predation can also arise from hunting by
humans, but they remain less documented. Advances in biologging allow
detailed assessments of the activity budgets of elusive wildlife,
increasing the potential to uncover the non-consumptive effects of human
activities on animals. We used tri-axial accelerometry to record the daily
activity of 24 Scandinavian brown bears (20 females and four males) from a
heavily hunted population in Sweden, for a total of 29 bear-years
(2015-2022). We used a random forest algorithm trained with observations
of captive brown bears to classify the accelerometry data into four
behaviours, running, walking, feeding, and resting, with an overall
precision of 95%. We then used these classifications to evaluate changes
in bear activity budgets before and during the hunting season. Bears
exhibited a bimodal daily activity pattern, being most active at dusk and
dawn, and resting around midday and midnight. However, during the hunting
season, males became more nocturnal compared to before the hunting season,
suggesting a proactive behavioural adjustment to reduce encounters with
hunters. Females showed the opposite pattern and had a higher probability
of being active during the day, potentially to increase nutritional gains
before denning. Additionally, daily number of running bouts did not vary
between the pre-hunting and hunting seasons in both sexes, but females’
proportion of running bouts occurring during legal hunting hours was
higher during the hunting season than prior to it, which suggest a
reactive behavioural adjustment to encounters with hunters. Detailed
assessments of wild animal behaviours, allowed through recording of
movement data at high frequencies, have the potential to improve our
understanding of the impacts of human activity on wildlife.