Feather mite abundance increases with uropygial gland size and plumage yellowness in Great Tits Parus major

摘要

Plumicolous feather mites are ectosymbiotic organisms that live on bird feathers. Despite\udtheir abundance and prevalence among birds, the ecology of the interaction between these\udorganisms and their hosts is poorly known. As feather mites feed on oil that birds spread\udfrom their uropygial gland, it has been hypothesized, but never tested, that the number of\udfeather mites increases with the size of the uropygial gland of their hosts. In this study the\udnumber of feather mites is considered with respect to uropygial gland size in a breeding population\udof Great Tits\udParus major\udin order to test this hypothesis. As predicted, the number\udof feather mites correlated positively with the uropygial gland size of their hosts, showing\udfor the first time that uropygial gland size can explain the variance in feather mite load among\udconspecifics. Previous studies relating feather mite load to plumage colour have suggested\udthat feather mites may be parasitic or neutral. To confirm this, the yellowness of breast feathers\udwas also assessed. However, the results ran in the opposite direction to that expected,\udshowing a positive correlation between mite load and plumage yellowness, which suggests\udthat further work is needed to give clear evidence for a specific nature of feather mites. However,\udGreat Tits with higher mite loads had lower hatching and breeding success, which may\udsupport the idea that feather mites are parasites, although this effect must be taken with\udcaution because it was only found in males. Age or sex effects were not found on the number\udof feather mites, and it is proposed that hormonal levels may not be sufficient to explain\udthe variation in feather mite loads. Interestingly, a positive correlation was detected between\uduropygial gland size and plumage brightness, which could be a novel factor to take into\udaccount in studies of plumage colour.