Nesting hoopoes cultivate in their uropygial gland the microbial symbionts with the highest antimicrobial capacity.

The European hoopoe (Upupa epops) conforms a paradigmatic example of animals cultivating bacteria in their uropygial gland that protect them against pathogenic infections. We here explore the hypothesis that enterococci are the responsible bacteria of such beneficial effect. We did so by comparing the antimicrobial activity against three indicator bacteria of colonies isolated from cultures of enterococci and mesophilic bacteria from the uropygial skin or secretion of nestlings, brooding or non-brooding females, and males of the subspecies longirostris in Hainan (China). In accordance with the hypothesis, enterococci isolated from nesting birds are more active than those from non-nesting birds. Moreover, enterococci from the uropygial secretion were more active than those isolated from the skin or than mesophilic bacteria isolates. These results therefore support the hypothesis that, during the nesting phase, hoopoe females and nestlings cultivate enterococci in their uropygial gland with relatively high antimicrobial activity.