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Egg Rejection Did Not Clearly Increase After Cuckoo Arrival in Two Host Species

Male Siberian stonechat perched on a reed
Research · Behaviour

Common cuckoos (Cuculus canorus) lay eggs in other birds’ nests, leaving the hosts to rear the cuckoo chick. One host defence is to recognise and reject a foreign egg. In Liuzhi, China, grey bushchats (Saxicola ferreus) and Siberian stonechats (Saxicola maurus) showed no clear increase in egg rejection after cuckoos arrived at their breeding grounds. The result gave no support to the idea that these hosts strengthen egg rejection over the short term as the seasonal risk of brood parasitism rises.

The two closely related hosts differ in how well they recognise foreign eggs. Researchers used two types of experimental egg to create moderate and low rejection levels, then compared the birds’ responses before and after the cuckoo’s migratory arrival. This allowed them to test whether egg-recognition ability or the type of foreign egg changed how the hosts responded to the seasonal shift in parasitism risk.

The analyses did not support a clear before-versus-after change in rejection rate for either host, regardless of their differing egg-recognition ability or the experimental egg type. In other words, the arrival of the brood parasite did not predict a stronger egg-rejection response in either species under the conditions tested.

The authors therefore found no support for within-season adjustment of egg rejection in these two species. They suggest that future work examine other sources of variation within host populations, including anti-parasite adaptations, breeding experience associated with age structure and mating systems.

Sources and image credit

  1. Risk of cuckoo parasitism does not predict egg rejection behaviour in two sympatric breeding hostsPrimary research article published 1 September 2026. The study compared grey bushchat and Siberian stonechat, two sympatric common cuckoo hosts with different egg-recognition abilities. Different experimental eggs created moderate and low rejection levels, and responses were compared before and after cuckoo migratory arrival. Neither host cognitive ability nor parasitic egg type had a significant effect on rejection rates before versus after arrival; the authors found no support for within-season adjustment of egg rejection to changing parasitism risk.

Image: Male Siberian stonechat in Salai, Uttar Pradesh, India, 24 November 2017. Photo: Charles J. Sharp / Wikimedia Commons. CC BY-SA 4.0. Representative species image; not a study bird. · CC BY-SA 4.0 · Source

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Behaviour

SPECIES IN THIS STORY

Species in this story

Common Cuckoo Cuculus canorus Explore species Siberian Stonechat Saxicola maurus Explore species

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