FEATHER MITES ON GROUP-LIVING RED-BILLED CHOUGHS - A NONPARASITIC INTERACTION

Most reports of interactions between feather mites and their avian hos ts have assumed that mites have detrimental effects on their hosts, i. e. that they behave as parasites. We investigate the effects of feathe r mites Gabucinia delibata on the body condition of Red-billed Choughs Pyrrhocorax pyrrhocorax, a highly social, medium-sized corvid species . Feather mites were absent in fledglings al the nest and were probabl y acquired by Choughs from 1 to 5 months after fledging, when they joi ned communal roosts. The abundance of feather mites on both wing and t ail increased with age and development of social habits in non-breedin g Choughs, but decreased when they reached breeding status. Mated Chou ghs had similar abundances of feather mites. The abundance of mites co rrelated positively with body condition (computed as the residuals of mass on a ''size factor'') in both males and females, and body conditi on was in general better for Choughs holding mites than for those lack ing mites. The conclusion that feather mites do not have detrimental e ffects on Choughs was reinforced by the fact that feather mite abundan ce did not differ between Choughs with normal and crossed bills, respe ctively, suggesting that preening does not remove mites from the feath ers. This particular association thus could be labelled as non-parasit ic, suggesting at least a commensal, and possibly a mutualistic relati onship. In the latter case, the hypothesised benefits accrued to Choug h hosts from their association with mites may derive from an improved feather cleaning, and from the supposed protection against pathogenic organisms achieved primarily by preemption of resources by more benign species, such as feather mites.