Quill mite infestation of rock ptarmigan Lagopus muta (Aves: Phasianidae) in relation to year and host age, sex, body condition, and density.

A total of 1209 ptarmigan were examined for Mironovia lagopus, including 721 juvenile birds (ca. 3 months old) and 488 adult birds (15 months or older). A total of 88 birds or 7.3% (n = 1209, 95% cl 5.9-8.9%) were infested with M. lagopus. There was an age difference in prevalence of infection, and more adults (10.7%, n = 488, 95% cl 8.2-13.7%) than juveniles (5.0%, n = 721, 95% cl 3.6-6.8%) were infested. There was a significant age effect in the mean intensity index, and adult birds had more advanced infestations compared with juvenile birds. There were no significant changes in either the interannual prevalence of infection or the mean intensity index of infection. Of the feather types inspected, there was no age-related difference in selection of feathers, nor was there any preference of mites for any one of the inspected feather types. Body dispersants were all adult females. There was an age-related difference in mean intensities of infection of body dispersants; it was higher in adult birds. The methods used to determine presence or absence of M. lagopus were not 100% accurate especially for juvenile hosts, and this at least partly explains the difference in prevalence among age groups. There was no relationship between host body condition or host density and infection by M. lagopus.