Feathers say a lot about a bird, so males and females invest a lot in protecting their plumage. According to Magdalena Ruiz-Rodríguez from the University of Granada, Spain, the bacteria Bacillus licheniformis is a major threat to a hoopoe's plumage, digesting the feather's keratin barbs with an enzyme. And nestlings are particularly at risk from feather damage, harbouring hordes of the bacteria in their filthy hole-nests as their feathers grow prior to fledging. However, another bacteria that is carried by hoopoes, Enterococcus faecalis, produces antibiotics against the feather-feasting bugs. Realising that E. faecalis hitch a lift in the hoopoe's uropygial gland, which produces secretions that the birds use while preening to protect their feathers, Ruiz-Rodríguez and her colleagues wondered whether the E. faecalis' antibiotics may protect the hoopoe's plumage from B. licheniformis damage (p. 3621).
Collecting breast feathers from male and female hoopoes, the team first sterilized the feathers then incubated them for a week in mixtures of the bacteria and one of the E. faecalis antibiotics to see whether E. faecalis and its antibiotic may protect the feathers from degradation. Scrutinizing the feathers with scanning electron microscopy, Ruiz-Rodríguez could see that the the feathers were completely ravaged by B. licheniformis, but in preparations where the B. licheniformis had been mixed with E. faecalis, or its antibiotic, the feathers were almost unharmed. And when the team searched for the tell tale bacterial plaques that signify a B. licheniformis infection, they only found the plaques on feathers incubated with B. licheniformis. Feathers incubated with E. faecalis and B. licheniformis, or the antibiotic and B. licheniformis were free of the feather degrading bacterial plaques.
Finally, to confirm that B. licheniformis was digesting the feathers' protein, keratin, the team incubated the feathers with the bacteria for 2, 5 and 16 days, and measured the amount of protein that had been released from the feathers. Enterococcus faecalis slowed the damage done by B. licheniformis, while the antibiotic completely stopped B. licheniformis from digesting the feathers.
Ruiz-Rodríguez and her team suspect that the protective power of hoopoe's uropygial gland secretions is due in part to the gland's E. faecalis population and the antibiotics that the bacteria produce. And the team back up their suggestion with the observation that both nestlings and incubating females spread the antibacterial uropygial gland secretions through their feathers while sitting in their nests.