Female common cuckoo calls dampen the mobbing intensity of great reed warbler hosts

To avoid mobbing attacks by their hosts during egg laying, some avian brood parasites have evolved traits to visually and/or acoustically resemble predator(s) of their hosts. Prior work established that reed warblers (Acrocephalus scirpaceus), a small host species of the brood parasitic common cuckoo (Cuculus canorus), delayed returning to the nest when confronted by either the calls of the female cuckoo or that of the predatory sparrowhawk (Accipiter nisus). It remains less clear, however, whether female cuckoo calls also suppress the nest defences of larger and more aggressive hosts. Such hosts typically attack vigorously, and can even hurt the brood parasitic intruders, instead of fleeing in the face of danger. Here, we tested whether the female cuckoo calls dampen mobbing intensity in a much larger Acrocephalus host of the common cuckoo, the great reed warbler (A. arundinaceus). We presented great reed warbler pairs with female common cuckoo models at their nests without and then with playing back the female-specific bubbling calls of the cuckoo. As controls, we tested the hosts' responses to harmless collared dove (Streptopelia decaocto) models, also without and then with the playbacks of dove calls. We found that the playback of female brood parasite calls reduced the aggression of hosts towards the cuckoo models as compared to model presentations without female calls, but we detected no such effect of the control calls with dove models. Our results revealed that female cuckoo calls effectively suppress the antiparasitic responses of great reed warbler hosts, which could aid parasites to approach the nest undiscovered and to evade the costly attacks of this large host. Therefore, the female call can be regarded as a general part of the cuckoo's trickery repertoire for successful parasitism.

Automated summary

The study showed that female brood parasite calls effectively reduce the aggression of great reed warbler hosts, enabling parasites to approach the nest stealthily and avoid attacks from the larger host bird.