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Foster-Host Diet Differences Covaried With Gut Microbiome Differences in Common Cuckoo Nestlings

Juvenile common cuckoo, representative species image
Research · Disease, parasites & microbiology

Common cuckoo (Cuculus canorus) nestlings raised by three different host species received different diets, and those dietary differences covaried with differences in their gut microbial communities and functional gene profiles. The study was conducted in China. The study, available online on 16 June 2026, combined three molecular approaches. Diet DNA metabarcoding identified prey from DNA remaining in faecal samples; 16S rRNA gene sequencing described the bacterial community; and metagenomic sequencing examined microbial genes and their functional potential.

The researchers compared cuckoo nestlings reared by oriental reed warbler (Acrocephalus orientalis), daurian redstart (Phoenicurus auroreus) and grey bushchat (Saxicola ferreus). Because brood-parasitic cuckoo chicks depend entirely on food delivered by their foster parents, the three host species provided a natural way to examine how different host-provided diets covary with the developing gut microbiome.

The three host groups provided different diets

Both dietary composition and Shannon diversity differed among cuckoo nestlings raised by the three host species. Shannon diversity combines how many prey types are present with how evenly feeding is distributed among them. The result therefore means that the foster hosts differed not only in which prey they delivered, but also in the diversity structure of the chicks’ diets.

Gut microbial Shannon diversity, however, did not differ clearly among the three cuckoo groups. Microbial community composition did. In other words, the groups could have broadly similar overall bacterial diversity while differing in which bacteria were present and in their relative abundances. A similar diversity value therefore did not mean that the microbiomes were biologically identical.

Microbial function differed most strongly in one host context

The metagenomic functional profile of the gut microbiome in cuckoos raised by oriental reed warblers differed from that of chicks raised by daurian redstarts and grey bushchats. The latter two groups were functionally more similar to each other. The authors discuss this as a form of functional redundancy: bacterial communities can differ in taxonomic composition while retaining partly similar metabolic capacities.

Across samples, greater dissimilarity in diet was associated with greater dissimilarity in both microbial community composition and metagenomic function. Several prey families were also associated with particular microbial genera and functional features. These are covariation patterns: because the study compared naturally reared chicks rather than experimentally assigning diets, it does not show that diet alone caused the microbiome differences.

The authors conclude that diet and gut microbiome composition and function covary in common cuckoo nestlings raised by different host species. They suggest that these associations may be relevant to nutrient acquisition under contrasting foster-host diets. The study therefore links a distinctive feature of brood parasitism — being fed entirely by another species — with variation in the microbial environment developing inside the cuckoo chick, while leaving the relative roles of diet and other host-rearing conditions for future causal tests.

Sources and image credit

  1. Zhang, L., Yu, J., Yuan, X., Zhong, G., Ma, L., Jin, L., Liang, W., & Wang, H. (2026). Associations between diet and the gut microbiome in brood-parasitic nestlings: Common Cuckoos reared by three host species. Avian Research, 17(4), 100402. https://doi.org/10.1016/j.avrs.2026.100402Primary open-access research article. Wild Common Cuckoo nestlings reared by Oriental Reed Warbler, Daurian Redstart and Grey Bush Chat received significantly different diets; dietary dissimilarity was positively associated with differences in gut microbial composition and predicted function.

Image: PJeganathan / Wikimedia Commons — juvenile Common Cuckoo (Cuculus canorus) photographed at Mordham Dam near Nagpur, India, 19 August 2014; representative juvenile species image, not a study bird; cropped to 16:9 from the original · CC BY-SA 4.0 · Source

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