Proactive and reactive movement behaviours shape the antipredator sequence in a large herbivore

Prey species can display antipredator movement behaviours to reduce predation risk, including proactive responses to chronic or predictable risk, and reactive responses to acute or unpredictable risk. Thus, at any given time, prey movement choice may reflect a trade-off between proaction and reaction. In previous studies, proaction and reaction have generally been considered separately, which neglects their potentially simultaneous influence on animal movement decisions and overall space use.

In this study, we analysed how proaction and reaction interact to shape the movements of GPS-collared red deer (Cervus elaphus) in response to hunting by humans. Using an exhaustive inventory of red deer hunting events and very high-resolution canopy cover density (LiDAR), we combined movement metric (displacement and path length) models and integrated step selection functions to investigate antipredator movement responses to lethal risk on various spatiotemporal scales, considering a dynamic landscape of risk.

Our results show that red deer either proactively avoided areas of chronic risk, or they selected canopy cover where and when risk was predictably high. However, when risk was encountered anyway, canopy cover was no longer selected, but only modulated a reactive response along a remain-to-leave continuum. This reaction was even more evident when the environment was unfamiliar, underlining the importance of memory in such reaction patterns.

We describe how proaction and reaction fuse in an antipredator sequence of interconnected movement decisions in a large herbivore, and discuss how this result may help disentangle the ecological consequences of behavioural responses to predation. Finally, we lay the foundations for further investigations into the origins of similarities and differences between proactive and reactive movement responses.