Sexual differences in the behavioural response to a variation in predation risk

Predators may influence their prey populations not only through direct lethal effects, but also by causing behavioural changes. The natural expansion of the wolf (Canis lupus) into the Alps provided the rare opportunity to monitor the responses of a prey species to the return of a large predator. Density effects have rarely been considered in the study of antipredator strategies. We examined the effects of wolf recolonisa‐ tion and density modifications on group size and use of safe areas by Alpine ibex (Capra ibex) in Gran Paradiso National Park (Italy), where no large terrestrial predator has been present for about a century. We documented that, in a few years, the vari‐ ation in the factors affecting the landscape of fear caused significant modifications in ibex behavioural patterns that could not be accounted for by density changes only. Male groups decreased in size and moved closer to safer areas. The distance of fe‐ male groups from refuge sites, instead, was not affected, and their propensity to live in groups was scarcely modified. Behavioural modifications likely caused a reduction in nutrient intake in adult male ibex, as they necessarily used lower‐quality feeding patches. Our results showed that male and female ibex, which are characterised by a strong dimorphism, adopted different strategies to solve the conflicting demands of foraging efficiently and avoiding predators.