Stability of chewing louse (Phthiraptera: Amblycera and Ischnocera) populations infesting great horned owls (Aves: Strigidae)

The annual abundance of chewing lice (Phthiraptera) was recorded on great horned owls (Bubo virginianus (Gmelin), Aves: Strigidae) from 1994 to 2015 in Manitoba, Canada. Kurodaia magna Emerson (Amblycera: Menoponidae) had a mean annual abundance about half that for Strigiphilus oculatus (Rudow) (Ischnocera: Philopteridae). Mean intensity, rather than prevalence, explained the variation in annual abundance. Temporal variation (measured as population variability) in abundance and mean intensity were high and similar (0.62-0.67), but lower for nymph to female ratio (0.36-0.38). Temporal variation of prevalence and sex ratio were higher for K. magna (0.34-0.35) than for S. oculatus (0.21-0.22), and typical for other louse species. The high temporal variability for abundance and mean intensity suggest lower year-to-year stability than exhibited by other chewing lice, but over 80% of this variability was due to sampling error resulting from small sample sizes in some years and extreme intensities in the aggregated distributions of intensity. The remaining variation, < 20%, revealed no significant differences in annual abundance or mean intensity among years, and therefore stable populations over 22 years. Populations of 12 species of chewing lice show lower temporal variability and therefore greater stability than three other insect taxa.