Feather mites are members of several very diverse groups of mites present in almost all groups of birds. They feed mainly on secretions of the uropygial gland of birds. This gland, probably better known as the preen gland or the oil gland, produces preen oil which is believed to help maintain the integrity of the feather structure, provide waterproofing, and - ironically - is supposed to have an anti-parasitic effect.
The nature of the biological relationship between feather mites and birds is still poorly understood, and empirical studies show a puzzling scenario: some studies have shown that feather mite abundance correlates positively with bird's body condition, while others have found no significant correlation or even negative correlations. In other words it is unclear if feather mites represent true parasites or commensals. Generally, they are thought of as ectoparasites and in some cases they really cause problems for the affected bird (e.g. feather damage).
One of the reasons for the lack of knowledge on their life history might be the fact that feather mite species identification is a really difficult task. Females and immature stages of many taxa are often indistinguishable, and even for males that usually carry the characteristic species traits, accurate identification requires advanced taxonomic skills and a lot of time and patience.
A group of researchers from Spain and Russia wanted to know if the situation could be changed for the better if DNA Barcoding is used:
Here, we tested DNA Barcoding as a useful molecular tool to identify feather mites from passerine birds. Three hundred and sixty-one specimens of 72 species of feather mites from 68 species of European passerine birds from Russia and Spain were barcoded.
The colleagues determined that a 200-bp minibarcode region showed the same accuracy as the full-length DNA Barcode and in addition that it is flanked by regions sufficiently conserved to make them potentially useful for group-specific primers.
Species identification accuracy was perfect (100%) but decreased when singletons or species of the Proctophyllodes pinnatus group were included. In fact, barcoding confirmed previous taxonomic issues within the P. pinnatus group. Following an integrative taxonomy approach, we compared our barcode study with previous taxonomic knowledge on feather mites, discovering three new putative cryptic species and validating three previous morphologically different (but still undescribed) new species.