The cloacal microbiome of a cavity- nesting raptor, the lesser kestrel (Falco naumanni)

Background. Microbial communities are found on any part of animal bodies exposed to the environment, and are particularly prominent in the gut, where they play such a major role in the host metabolism and physiology to be considered a ``second genome''. These communities, collectively known as ``microbiome'', are well studied in humans and model species, while studies on wild animals have lagged behind. This is unfortunate, as different studies suggested the central role of the gut microbiome in shaping the evolutionary trajectories of species and their population dynamics. Among bird species, only few descriptions of raptor gut microbiomes are available, and mainly carried out on captive individuals. Objectives. In this study, we aimed at improving the knowledge of raptor microbiomes by providing the first description of the gut microbiome of the lesser kestrel (Falco naumanni), a cavity-nesting raptor. Results. The gut microbiome of the lesser kestrel was dominated by Actinobacteria (83.9%), Proteobacteria (8.6%) and Firmicutes (4.3%). We detected no differences in microbiome composition between males and females. Furthermore, the general composition of the microbiome appears similar to that of phylogenetically distant cavity-nesting species. Conclusions. Our results broaden the knowledge of raptor gut microbial communities and let us hypothesize that the distinct nest environment in terms of microclimate and presence of organic material from previous breeding attempts, to which cavity- nesting species that reuse the nest are exposed, might be an important driver shaping microbiomes.