Does water-bath cleaning affect the health of visiting birds? A study of parasite loads in house finches (Haemorhous mexicanus) in the Phoenix, Arizona, USA metropolitan area (2018)

There is evidence that urban animals have higher parasite and pathogen burdens than those from natural areas, but the mechanism behind this pattern is unclear. One possibility for yard-visiting birds is that they drink from bird baths that have not been regularly cleaned and thus they have elevate infection risks and rates by consuming unusually soiled water. We experimentally tested this idea in house finches (Haemorhous mexicanus) – a common backyard visitor in North America – by implementing a rotating bath-cleaning regime, where we either left baths uncleaned for 5 weeks or cleaned them daily with dilute bleach for 5 weeks, and did so at both an urban and rural study site. We found that coccidian endoparasitism decreased in urban birds when they drank from clean baths, but the same was not true for rural birds. These results reveal a habitat-specific effect of feeder cleaning on disease status in an abundant yard-visiting songbird.