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Cuckoo Calls Did Not Change Egg Rejection by Red-backed Shrikes

Female red-backed shrike perched in a tree in Biebrza National Park, Poland
Research · Behaviour

Red-backed shrikes (Lanius collurio) rejected artificial common cuckoo (Cuculus canorus) eggs at a high rate regardless of whether they heard calls from a female cuckoo, male cuckoo, sparrowhawk or a neutral control species. The playback study from eastern Poland was published on 22 January 2026 and tested 63 shrike clutches over two breeding seasons.

Researchers placed an artificial cuckoo egg in each nest and then played a three-minute recording of one of four sound types: female cuckoo, male cuckoo, Eurasian sparrowhawk (Accipiter nisus) or Eurasian collared dove (Streptopelia decaocto). The artificial eggs were modelled on museum specimens of cuckoo eggs found in red-backed shrike nests.

Museum and experimental red-backed shrike nests with common cuckoo eggs used in the playback study
The study compared artificial cuckoo eggs placed in red-backed shrike nests with natural cuckoo eggs from museum clutches. Figure 1 from Sulej & Goławski (2026), Behavioral Ecology and Sociobiology, CC BY 4.0. Source.

Almost nine out of ten artificial eggs were ejected

Overall, the shrikes removed the artificial egg from 88.9% of nests. Rejection exceeded 90% during egg-laying and early incubation and was lower later in incubation, but the effect of breeding stage was unclear.

The kind of sound played did not clearly change whether the artificial egg was rejected. Female and male cuckoo calls did not make rejection more likely than the other sounds, and neither the sparrowhawk playback nor time of day changed the response.

A strong defence that did not depend on short-term sound cues

The authors interpret the result in light of the red-backed shrike’s already strong egg-rejection behaviour. They suggest that a host capable of recognising and rejecting foreign eggs at such a high baseline rate may have little scope for additional auditory information to increase that response further.

No naturally cuckoo-parasitised shrike broods were found in the study areas during the research period. The authors describe the species as a former common cuckoo host whose strong rejection ability may represent a lasting legacy of earlier coevolution with the parasite.

Sources and image credit

  1. Sulej, A., & Golawski, A. (2026). Do common cuckoos’ vocalisations affect egg discrimination in the strong rejector red-backed shrike? Behavioral Ecology and Sociobiology, 80, 17. https://doi.org/10.1007/s00265-025-03689-yPrimary peer-reviewed open-access study, version of record published 22 January 2026.

Image: Frank Vassen — female red-backed shrike photographed at Gugny in Biebrza National Park, Poland; representative field image from the same country as the experiment, not from the experimental nests; Wikimedia Commons. · CC BY 2.0 · Source

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