Ectoparasites reduce long-term survival of their avian host

Few field studies have evaluated whether ectoparasites affect the long-term survival of their adult host, although many studies have examined the impact of parasites on the host's offspring. In the colonially nesting cliff swallow (Hirundo pyrrhonota), we manipulated ectoparasite load (of cimicid bugs, fleas, and chewing lice) by fumigating adults and comparing annual survivorship of fumigated birds and non-fumigated control birds captured at the same time. Mark-recapture experiments over an 8-year period revealed that non-fumigated birds had an annual survivorship about 12% less than chat of fumigated birds, on average, but the effects did not vary with colony size. Based on the difference in survivorship between fumigated and non-fumigated birds, we estimated that parasitized individuals had an annual survivorship of 0.38, compared with 0.57 for non-parasitized birds. The parasite-caused reduction in survivorship was the equivalent of the host losing up to one year of lifetime reproductive success. Ectoparasites did not preferentially infest hosts of lower quality, suggesting that all birds in the population were at potential risk of suffering parasitism and the resulting reductions in survivorship. Our results show that obligate ectoparasites such as fleas and lice impose a substantial long-term cost to their hosts and suggest that future studies of ectoparasitism should consider the parasites' effect on annual survival of adult hosts.