Kai-Philipp Gladow, Marla Jablonski, Nayden Chakarov, Oliver Krüger

The loss of top predators has been shown to lead to drastic changes in community structure. An important part of this is the shift in behavior of other species. The understanding of such changes is scarce because recordings of behavioral reactions towards lost species are rarely done. This is important for predators experiencing predation pressure themselves, known as intraguild predation. Re-colonizations offer the unique possibility to fill this knowledge gap. However, only a few studies tested experimentally how subordinate predators change their behavior towards top predators in comparison to other members of their guild. Birds adjust the level of nest defense in response to perceived threats. Therefore, we expected birds of prey in intraguild predation systems to show an appropriate level of nest defense against the predator they are faced with, with the highest level shown against the top predator. We tested this by placing models of eagle owls (Bubo bubo) and goshawks (Accipiter gentilis) close to nests of common buzzards (Buteo buteo) and measured the reaction. Additionally, we compared the development of the three populations and tested for other influences on the defense behavior. We did not find significant differences in aggression by common buzzards toward eagle owl and goshawk and therefore conclude that the top predator provokes a similarly high nest defense as another (meso-)predator. This shows that in ecological communities the top predators and mesopredators may not have separated levels from the viewpoint of intraguild prey. Top predators and mesopredators might be perceived as comparable threats.