The function of avian mobbing: an experimental test of ‘attract the mightier’ hypothesis

Various avian species give mobbing calls that draw conspecific and heterospecific individuals to react against the potential predator. According to the ‘attract the mightier’ hypothesis, when predators appear, prey will produce mobbing calls to attract superior predators to repel or kill the primary predator. To test this hypothesis, we broadcast calls from light-vented bulbuls, Pycnonotus sinensis (the prey) in the vicinity of a taxidermy model of a collared scops owl, Otus lettia (the primary predator). Three call types were used: the typical call (TC, the control treatment), a mobbing call to a collared scops owl (the MtO treatment) and a mobbing call to a crested goshawk, Accipiter trivirgatus (the superior predator; the MtH treatment). Our results showed that crested goshawks appeared and attacked the taxidermy model during the MtO treatment, but not during the control or MtH treatment. The difference between the MtO and other treatments was significant. Our results, therefore, provide strong evidence for the hypothesis that mobbing calls to primary predators can successfully attract superior predators to harm primary predators.