The effects of an ectoparasite on reproductive success in the great tit: a 3-year experimental study

The effects of ectoparasites on host reproductive success have been studied in a variety of bird species. Most of these studies concern either colonial or hole-nesting birds, which have been suspected of being particularly susceptible to parasites because of their social habits and (or) reuse of old nests. The effects of a horizontally transmitted flea, Ceratophyllus gallinae, on the reproductive success of hole-nesting great tits, Parus major, were experimentally studied over 3 years. Leaving nests in nest boxes in the intervals between breeding seasons does not result in a significant increase in parasite abundance in comparison with nest boxes cleaned between seasons. Flea abundance was reduced by spraying random nests with an insecticide during host egg laying. There were no significant effects of ectoparasite removal on clutch size, number of fledged young, hatching success, or fledging success in any of the 3 years, although a significant interaction between year and treatment in nestling body mass was observed. Thus, in 1 of the 3 years, body mass of nestlings in the sprayed boxes was, on average, significantly greater than that of controls. There was also a negative correlation between flea abundance and mean body mass of the brood. In addition, nestlings produced in flea-free boxes had a significantly higher probability of recruiting locally than nestlings from control nests. The effects of ectoparasites seem to vary over time and also among host populations, which implies that the effects of parasites may interact with other environmental factors.