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

Abstract

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.

Testing the Interspecific Function of Female Common Cuckoo “Bubbling” Call

“…Another interesting finding is that an interspecific function of female common cuckoo "bubbling" calls was not supported in the study, as the induced vigilance during cuckoo call playback was similar to that of the negative control (oriental turtle dove calls) and significantly lower than that of the positive control (common kestrel calls). This finding contradicts the findings of previous research (York and Davies, 2017;Jiang et al, 2021;Marton et al, 2021). The target species in previous studies always remained in an open area in the beginning of the experiments.…”

“…In the playback sounds, the rate was adjusted to 1 call per 10 s. A total of four 90-s playback sounds were generated, and two 15-s breaks were inserted after 30 and 60 s to generate 2-min playback sounds. The rhythm of these sounds was similar to the playback sounds used in a previous study (Marton et al, 2021).…”

“…The target species in previous studies always remained in an open area in the beginning of the experiments. For example, York and Davies (2017) presented playbacks to tits at experimental feeders; Jiang et al (2021) presented playbacks to domestic chickens inhabiting open areas; Marton et al (2021) started to broadcast playbacks after great reed warblers showed mobbing behavior to a cuckoo decoy. In this study, target individuals were perched on dense reeds.…”

“…Recordings from 9 individuals were downloaded for each species, and one call from each individual was used. Similar to a previous study (Marton et al, 2021), the rate was adjusted to 1 call per 10 s, and then two 15-s breaks were inserted after 30 and 60 s, generating four 2-min long playback sounds.…”

“…This predatorlike call diverts the attention of reed warbler (Acrocephalus scirpaceus) parents and reduces the egg rejection rate (York and Davies, 2017). Playback of this call can effectively suppress the mobbing intensity of great reed warblers (Acrocephalus arundinaceus) (Marton et al, 2021). Even unsuitable hosts can be deceived.…”