Characterizing bacterial communities of wild birds: Insights from three southern African hornbill species

The microbiome of the uropygial gland and integuments where birds spread the uropygial secretion may play crucial roles for their hosts, but it has been poorly studied, especially in wild species. Exploring bacterial communities associated with the uropygial secretion of birds is particularly interesting in species under strong selection pressures due to pathogenic infection. Here, by high-throughput 16S rRNA amplicon sequencing, we characterized and compared the bacterial communities of the uropygial gland surface of three African hornbill species (Family Bucerotidae), as well as the bill and feathers of females from two of these species and the nestlings of the other one. In accordance with previous knowledge of avian microbiomes, we expected to find differences associated with species identity, age and the sampled integument. Overall, we found that: 1) the microbiome was similar among species, 2) but there were slight differences associated with the sampled body regions. Moreover, 3) we observed no consistent variation in the microbiota with age, and 4) females and nestlings sharing a nest harboured more similar gland surface microbiota compared to females and nestlings that did not share a nest. These species often reuse nest cavities, sealing them with a plug made from diverse material. Once sealed, they remain enclosed in the nest for a long period. This behaviour opens the possibility that the nest environment is key shaping the microbiota of these species and might serve as a reservoir of the sampled bacterial communities. Moreover, behavioural mechanisms such as preening may contribute to the transmission of bacteria from the uropygial gland to other body regions, enhancing bacterial similarities. This study contributes to our understanding of the role of the nest environment in structuring bacterial communities in wild birds and provides the first thorough characterization of the microbiome inhabiting different body integuments of southern African hornbills.