Experimental comparison of defence behaviour against different avian top predators in an intraguild prey

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 behaviour of other species. The understanding of such changes is scarce because recordings of behavioural 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 behaviour towards differently sized top predators. Birds adjust the level of nest defence in response to perceived threats. Therefore, we expected birds of prey in intraguild predation systems to show an appropriate level of nest defence against the predator they are faced with, with the highest level shown against the largest 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. Overall, aggression by common buzzards towards eagle owls was greater than towards goshawks, but effect sizes were small and had relatively large confidence intervals. We therefore conclude that the largest predator and the second-largest predator provoke similarly high nest defences. This shows that in ecological communities the largest predator and smaller predators may not belong to different categories from the viewpoint of intraguild prey. Different top predators might be perceived as comparable threats.