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Closer Relatives Among Hoopoes, Woodhoopoes and Hornbills Had More Similar Preen-Gland Microbiomes

Wild Eurasian hoopoe
Research · Disease, parasites & microbiology

More closely related birds in the order Bucerotiformes had more similar bacterial communities in the secretion of their uropygial, or preen, glands. This gland at the base of the tail produces a secretion that birds spread through the plumage while preening. The study, published on 7 August 2026, tested whether the gland microbiome followed the evolutionary relationships among hoopoes, woodhoopoes and hornbills.

The researchers compared eight Bucerotiformes taxa: three subspecies of Eurasian hoopoe (Upupa epops), two woodhoopoe species and three hornbill species, including the southern yellow-billed hornbill (Tockus leucomelas). European rollers were included as an outgroup for comparison. Samples came from breeding birds in Spain, Switzerland, Namibia, South Africa and China. The bacterial communities were characterised from preen-gland secretions of 69 hoopoes, 17 woodhoopoes and 59 hornbills, with 24 rollers as the outgroup. Researchers used high-throughput sequencing of a region of the bacterial 16S rRNA gene, a commonly used genetic marker for distinguishing bacterial lineages and comparing the composition of microbial communities.

The microbiome followed host relatedness

Differences between the bacterial communities correlated with the evolutionary distances between the bird taxa: close relatives tended to have more similar microbiomes. This pattern is known as phylosymbiosis — the composition of a host-associated microbial community reflects the host phylogeny more closely than expected by chance.

Phylosymbiosis does not by itself prove that the bacteria and birds evolved together. The authors discuss both inherited host traits and species-specific ecology as possible influences on which bacteria can persist in the gland. They also note that some distantly related study taxa lived in the same regions, while the three hoopoe subspecies were sampled on different continents, making geography alone an unlikely explanation for the phylogenetic pattern.

Antimicrobial function showed a different pattern

Hoopoes and woodhoopoes are known to harbour symbiotic bacteria in the gland that can produce antimicrobial compounds. In the new study, the researchers cultured bacterial isolates and measured how strongly they inhibited three indicator bacteria. Antimicrobial activity did not increase or decrease consistently with host evolutionary distance.

Within hoopoes and woodhoopoes, however, the composition of the bacterial community was linked to antimicrobial activity, and the relative abundance of particular bacterial strains helped predict stronger or weaker inhibition. The authors therefore suggest that antimicrobial functions may contribute to the phylosymbiosis pattern, but the study does not establish a simple one-to-one relationship between host relatedness and antimicrobial activity.

Sources and image credit

  1. Barón, M. D., Martín-Vivaldi, M., Martínez-Renau, E., Arlettaz, R., Engelbrecht, D., Enkvist, C., Jansen van Rensburg, E. L., Zhang, L., Martín-Platero, A., Martínez-Bueno, M., Martínez-García, Á., Ruiz-Castellano, C., Schaub, M., Stanback, M., van de Ven, T. M. F. N., Videvall, E., Liang, W., & Soler, J. J. (2026). Functional phylosymbiosis in birds: phylogeny and antimicrobial properties of bacterial symbionts in Bucerotiformes. Animal Microbiome. https://doi.org/10.1186/s42523-026-00608-yPrimary peer-reviewed open-access article published 7 August 2026 under CC BY 4.0. The study compared uropygial-gland bacterial communities and antimicrobial activity across eight Bucerotiformes taxa sampled in Spain, Switzerland, Namibia, South Africa and China, with European roller as an outgroup.

Image: Anagha devi / Wikimedia Commons — wild Eurasian hoopoe (Upupa epops) photographed in Tadoba-Andhari Tiger Reserve, India, 18 December 2019; CC BY-SA 4.0. Representative image of one central study species, not a sampled bird. · CC BY-SA 4.0 · Source

About this content: This story was produced with AI assistance within an editorial workflow developed by Wildlife Vagabond. Editorial responsibility remains with Wildlife Vagabond.How AI is used

Disease, parasites & microbiology

SPECIES IN THIS STORY

Species in this story

Eurasian Hoopoe Upupa epops Explore species African Hoopoe Upupa africana Explore species Southern Yellow-billed Hornbill Tockus leucomelas Explore species

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