Apparent lack of effects of a high louse-fly infestation (Diptera, Hippoboscidae) on adult colonial Alpine Swifts

A population of Alpine Swifts (Apus melba) showed the highest louse-fly parasitization rate (74%) as far as known in birds. This might be caused by a limited ability to preen. The prevalence was lower in second-year birds than in adults, probably as a result of their breeding status. Parasitization affected neither body condition, nor the probability of trans mission of blood parasites. Due to mobility of louse flies, we suggest that heavy infestations have a short duration, and thus do not affect individual Swifts in terms of physical deterioration.