Some adult obligate avian brood parasites, including the common cuckoo (Cuculus canorus), evolved traits to mimic predators to threaten adult hosts and to increase the rate of parasitism success. We tested whether the bubbling call of adult female common cuckoos, considered to resemble the calls of predatory sparrowhawks (Accipiter nisus), had an effect on the mobbing intensity of nesting great reed warblers (Acrocephalus arundinaceus), a large and highly aggressive cuckoo host. We found that the mobbing intensity of this host species decreased in response to cuckoo decoys coupled with the bubbling call playback relative to presentations of the cuckoo decoys alone, while we found no such decrease when the hosts were presented with collared dove (Streptopelia decaocto) decoys with or without the dove call playbacks.