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Female Common Cuckoos Gave No Bubbling Call in 282 of 284 Recorded Parasitism Events

Common cuckoo perched in natural vegetation
Research · Behaviour

Female common cuckoos (Cuculus canorus) almost never gave their distinctive bubbling call while laying in host nests in an 11-year video dataset from China and the Czech Republic. The researchers analysed 284 recorded parasitism events at nests of oriental reed warbler (Acrocephalus orientalis) and great reed warbler (Acrocephalus arundinaceus).

In 282 of the 284 events, no bubbling call was detected during the recorded parasitism event. Calls were heard in only two cases, both at great reed warbler nests in the Czech Republic, and in both they occurred shortly after parasitism, once the cuckoo had moved outside the camera’s field of view. The authors therefore note that the caller cannot be identified with complete certainty as the same female that had just parasitised the nest.

Female common cuckoo at a host nest with an egg in its bill
A female common cuckoo at a host nest during parasitism, with a host egg in its bill. Study image from Wang et al. (2026), Journal of Vertebrate Biology, CC BY 4.0.

The cuckoos were mobbed in both events with bubbling calls

In both events associated with bubbling calls, the parasitising cuckoo was mobbed. In one case the great reed warbler hosts attacked the cuckoo; in the other, the hosts were absent during parasitism but a sedge warbler (Acrocephalus schoenobaenus) mobbed the female. The authors therefore argue that the observations do not support the idea that the bubbling call normally functions as a counter-defence that distracts or misdirects aggression during egg-laying.

The study was designed to assess this proposed function under natural parasitism conditions. It combined long-term video surveillance from two major host systems in Europe and Asia rather than relying on playback experiments alone.

Behaviour at the nest may constrain vocalisation

The authors also discuss practical features of the laying event that can make calling difficult. Host attacks were not merely occasional in the video material. In every event in which the hosts were present close to the parasitising female — 67 oriental reed warbler events and 25 great reed warbler events — they attacked the cuckoo, encouraging her to keep her head low while laying. Females also removed and held a host egg in the bill in 67 of 74 oriental reed warbler nests and 32 of 33 great reed warbler nests that contained eggs. Holding an egg in the bill is incompatible with producing the bubbling call with an open bill.

The authors present these observations as possible immediate behavioural reasons why vocalisation was so rare during the recorded parasitism events. At a broader evolutionary level, they suggest that the bubbling call may primarily serve functions outside the laying event — such as communication with males or territorial signalling — with any effect on host behaviour being secondary rather than the reason the call evolved.

Sources and image credit

  1. Wang, L., Večeřová, G., Šulc, M., Luo, H., Xiao, H., Liang, W., & Honza, M. (2026). Common cuckoo (Cuculus canorus) bubbling call does not serve as a counter-defence strategy in two warbler hosts in Europe and Asia. Journal of Vertebrate Biology, 75, 25098. https://doi.org/10.25225/jvb.25098Primary open-access research paper published in February 2026 under CC BY 4.0. Eleven years of video surveillance yielded 284 common cuckoo parasitism events in China and the Czech Republic; no bubbling call was detected in 282 events, while the two recorded calls occurred shortly after parasitism, outside the camera field of view.

Image: Alastair Rae — common cuckoo (Cuculus canorus) photographed in Georgia on 1 May 2017; representative species image, not a bird from the study. Source: Wikimedia Commons. · CC BY-SA 2.0 — https://creativecommons.org/licenses/by-sa/2.0/ · Source

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