“…At a lower taxonomic level, many genera dominating in CM, such as Enterobacter , Streptococcus , Enterococcus , Clostridium , Lactobacillus , Lactococcus , Turicibacter and members of the Ruminococcaceae family, are facultative symbionts or commensals inhabiting the digestive tracts of many vertebrate species [ 2 , 56 , 62 ]. We also detected several OTUs, such as Staphylococcus , Janthinobacterium , Corynebacterium , Aerococcus and Brevibacterium , that commonly colonise the skin’s surface [ 63 ] and OTUs associated with other parts of the animal’s body, such as Rothia , Porphyromonas Enhydrobacter and Actinobacillus , see for example [ 64 ]. Finally, barn swallow CM composition may also partly reflect the bird’s diet, which is composed of flying insects and other arthropods present in aerial plankton.…”