Cutaneous Lesions in the Gular Region Caused by Feather Follicle Infestation with Harpirhynchidae sp. Mites in Great Crested Flycatchers (Myiarchus crinitus) in New York, USA, 2016-23.

Great Crested Flycatchers (Myiarchus crinitus), migratory passerines with a breeding range throughout the northeastern, midwestern, and southern US, are banded annually at the Braddock Bay Bird Observatory located on the southern shore of Lake Ontario, New York, USA. In 2016, a Great Crested Flycatcher was observed with distinct lesions in the gular and ventral neck region, which prompted evaluation for similar lesions in subsequently trapped flycatchers and other passerine species. From 2016 to 2023, 62/102 banded Great Crested Flycatchers had their gular region examined, and seven were found to have lesions (11.3% incidence). Similar lesions were not found in any other species. Lesions were localized to the gular region and included extensive feather loss with thickened, corrugated, pale-yellow skin. Grossly visible 1- to 2-mm-diameter, raised, white-to-yellow foci throughout the affected region corresponded microscopically to feather follicles that were massively dilated with mites. Morphologic analysis of mites obtained from skin scrapes revealed that this mite species belongs to the family Harpirhynchidae. Mites in this family have restricted avian host ranges and cause varying clinical presentations in passerines, though many species remain unidentified. PCR efforts were unsuccessful in yielding a species-level identification. Further monitoring of Great Crested Flycatchers and other avian species is warranted, as the fitness implications of this ectoparasitism at the individual and population levels are not known.