Reduced parasite infestation in urban Eurasian blackbirds (Turdus merula): a factor favoring urbanization?

Humans nowadays dramatically alter environmental and ecological conditions worldwide. One of the most extreme forms of anthropogenic land-use alteration is urbanization. Animals thriving in urban areas are not only exposed to different environmental conditions compared with their nonurban conspecifics, but prevalence and impacts of wildlife diseases on urban populations may also be affected. In the present study, we tested whether blood-parasite prevalence differs between urban and forest habitats by comparing haematozoan infections of urban and forest-living Eurasian blackbirds (Turdus merula L., 1758). In total, 76% of Eurasian blackbirds were infected with haematozoa and we detected five different blood parasite genera in both habitats. Blood-parasite prevalence varied both between years and between spring and summer in both urban and forest populations. Forest blackbirds had more parasite genera per individual than urban blackbirds, and in summer, forest blackbirds had higher blood-parasite prevalence than their urban conspecifics. These differences in blood-parasite prevalence between urban and forest blackbirds suggest a lower risk of haematozoan infections in urban than in forest habitats. The lower parasite prevalence could be one of the factors favoring the invasion of urban ecosystems.