Ectoparasite and blood parasite prevalence in birds: a comparative study between urbanized airport environments and natural habitats

The rapid growth of urban populations and air travel has intensified urbanization's ecological impacts, reshaping ecosystems through habitat fragmentation, pollution, and species filtering. These effects are particularly evident in urban bird populations. In this study, we examined how urban environments, especially near airports, affect birds by evaluating relationships among parasites, feather corticosterone levels, and body condition. We hypothesized that birds near airports would experience higher parasite prevalence due to stress-related immune compromise. We sampled 1,096 birds from 100 species, recording haemosporidian parasite lineages and ectoparasites across three Brazilian airports, Brasília, Salvador, and Campinas, and corresponding quiet-control areas located 8-17 km away. Using Bayesian multilevel models, we accounted for species relatedness and environmental factors. Overall, 21.8% of birds were infected with haemosporidian parasites. Turdus leucomelas showed the highest infection rate (44%), with Plasmodium representing 63% of all infections. Ectoparasites infested 9.2% of birds, especially Elaenia chiriquensis. Fifteen individuals, mostly in Salvador and Campinas control sites, harbored both parasite groups. Contrary to expectations, haemosporidian prevalence was lower in airport areas than in control sites, while ectoparasites were less common in Brasília's control site. Feather corticosterone and body condition were not significantly associated with haemosporidian presence, but higher corticosterone correlated with ectoparasite occurrence in control areas. Our results indicate that bird populations around airports exhibit reduced parasite prevalence, suggesting that highly modified environments alter parasite-host dynamics and shape parasite biodiversity. Future studies incorporating infection intensity and longitudinal sampling would help clarify whether urban settings suppress or restructure avian parasite communities.