Variation in haematozoan parasitism at local and landscape levels in the red-billed quelea Quelea quelea

The red-billed quelea Quelea quelea, one of the most abundant birds in the world, presents two fundamental conundrums that we investigate here with a novel approach using blood parasite assemblages at two spatial scales, landscape and individual. The quelea of southern Africa Q. q. lathamii are split by a hypothesized migratory divide, where birds follow rain fronts in one of two directions (NW or SE). This divide is not detectable in the host population using microsatellite data, and here we show that it is also not apparent from our large-scale phylogeographical analyses of the haematozoan parasite. At a finer scale, the colourful and variable breeding plumage of male red-billed quelea has not previously shown a correlation with predictors of quality, as it does in many other bird species. The male's breeding plumage is partially based on carotenoid colouration, the quality of which has been correlated with haematozoan infection in other bird species. However, we found no correlation between intensity of male carotenoid colouration and haematozoan infection. Our results do not contradict the hypothesis that male breeding plumage in this species serves to identify individuals rather than to indicate quality. Finally, we recovered the greatest number of haematozoan lineages from any phylogenetic survey of a single host species to date. Understanding the reasons for the extreme diversity of parasite lineages in this species may assist in explaining the success of the red-billed quelea in anthropogenic landscapes.