Not so scary after all? Decoding the landscape of fear through hormonal responses to risky times and places

Abstract

Prey must balance the energetic benefits of foraging with avoiding predation risk. This risk-reward trade-off, a cornerstone of behavioural ecology, hinges not only on realized predation risk but also on how prey perceive that risk. We often assume energetically rewarding habitats must be inherently risky because prey often increase their vigilance in these habitats or avoid them altogether. However, our assumption that these antipredator behaviours reflect perceived risk frequently goes untested. We used non-behavioural data to test our assumptions about which habitats prey perceive as risky by pairing observations of habitat use of elk (Cervus canadensis) with their physiological responses measured from faecal hormones: glucocorticoids (GC), which reflect stress from perceived risk and hunger, and triiodothyronine (T3), which increases with energy intake. Elk had lower GC and T3 in the forest, a putatively safer and poorer foraging habitat than cropland, where they produced more T3, indicating foraging. Surprisingly, GC levels were consistent in cropland, even during the daytime when human activity--and putative risk--peaked. This lack of risk responsiveness highlights that physiological responses are a nuanced integration of perceived risk and reward rather than a guaranteed outcome of habitat use. Our study challenges the assumption that high-reward habitats are inherently risky, and that safer habitats limit energy intake, revealing that the assumptions we make about habitats from a behavioural lens may not always be the reality for prey.