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Grey Bushchats Rejected Foreign Eggs More Often Before Their Own Egg-Laying Began

Male grey bushchat perched on a branch
Research · Behaviour

Grey bushchats (Saxicola ferreus) in China changed how they recognised and rejected foreign eggs depending on the stage of their own laying cycle, according to a study published on 16 February 2026. The species is a host of the common cuckoo (Cuculus canorus), and the researchers tested how its anti-parasite responses worked before and after the first host egg had been laid.

During the pre-laying stage, grey bushchats showed significantly higher rejection of foreign eggs than after laying had begun. The authors interpret this as an “onset of laying” mechanism: an egg appearing before the female has started her own clutch can itself act as evidence that the egg does not belong there.

The first laying episode helped establish an egg template

The experiments also indicated that females could learn and retain the appearance of their own eggs during the first egg-laying episode. Once this short learning process had occurred, the birds could use the remembered egg phenotype when judging later eggs, even without their own eggs physically present in the nest at the time of the test.

This means the host did not rely on a single fixed recognition rule throughout breeding. Instead, the information available before laying and the learned appearance of its own eggs after laying began could both contribute to decisions about unfamiliar eggs.

Mimicry and the cost of deserting a nest also mattered

The authors found that rejection behaviour was also shaped by how closely a foreign egg resembled the host’s own eggs and by the trade-off associated with abandoning a nest. A well-mimicked egg is more difficult to distinguish, while deserting an entire nesting attempt can itself carry a reproductive cost.

Sources and image credit

  1. Zhong, G., Wang, L., & Liang, W. (2026). How the grey bushchat combats parasitic eggs at different laying stages. Journal of Evolutionary Biology, 39(4), 552–560. https://doi.org/10.1093/jeb/voag009Primary peer-reviewed article published online 16 February 2026. The study found significantly higher foreign-egg rejection before host laying began, evidence of short-term learning of the host’s own egg phenotype, and effects of egg mimicry and nest-desertion trade-offs.

Image: Jason Thompson — male grey bushchat (Saxicola ferreus) near the pagodas in Doi Inthanon National Park, Chiang Mai, Thailand, 7 December 2012; representative species image, not a bird from the study. Source: Wikimedia Commons. · CC BY 2.0 — https://creativecommons.org/licenses/by/2.0/ · Source

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