Abstract
Animals inhabiting urban areas often experience elevated disease threats, putatively due to factors such as increased population density and horizontal transmission or decreased immunity (e.g. due to nutrition, pollution, stress). However, for animals that take advantage of human food subsidies, like feeder-visiting birds, an additional mechanism may include exposure to contaminated feeders as fomites. There are some published associations between bird feeder presence/density and avian disease, but to date no experimental study has tested the hypothesis that feeder contamination can directly impact disease status of visiting birds, especially in relation to the population of origin (i.e. urban v. rural, where feeder use/densities naturally vary dramatically). Here we used a field, feeder-cleaning experimental design to show that rural, but not urban, house finches (Haemorhous mexicanus) showed increased infection from a common coccidian endoparasite (Isospora spp.) when feeders were left uncleaned and that daily cleaning (with diluted bleach solution) over a 5-week period successfully decreased parasite burden. Moreover, this pattern in rural finches was true for males but not females. These experimental results reveal habitat- and sex-specific harmful effects of bird feeder use (i.e. when uncleaned in rural areas). Our study is the first to directly indicate to humans who maintain feeders for granivorous birds that routine cleaning can be critical for ensuring the health and viability of visiting avian species.
Highlights
Animals inhabiting urban areas often experience elevated disease threats, putatively due to factors such as increased population density and horizontal transmission or decreased immunity
We performed this experiment with house finches (Haemorhous mexicanus), a popular backyard-bird subject for the study of avian disease dynamics[18,19]
We found no significant effect of any variable on presence of coccidiosis in rural birds (Fig. 1, Table 1)
Summary
Animals inhabiting urban areas often experience elevated disease threats, putatively due to factors such as increased population density and horizontal transmission or decreased immunity (e.g. due to nutrition, pollution, stress). We used a field, feeder-cleaning experimental design to show that rural, but not urban, house finches (Haemorhous mexicanus) showed increased infection from a common coccidian endoparasite (Isospora spp.) when feeders were left uncleaned and that daily cleaning (with diluted bleach solution) over a 5-week period successfully decreased parasite burden. Animals can leave disease-contaminated materials (e.g. blood, feces, eye discharge) on feeder surfaces that, if not cleaned, can foster and exacerbate transmission of blood-borne pathogens, endoparasites, and other microbes This raises the prospects of whether or not extensive soiling of feeders is responsible for elevating incidence or severity of certain pathogens and parasites, and whether or not routine feeder cleaning may be an effective means of reducing disease risk at feeding sites. We predicted that disease levels would rise during periods when feeders were not cleaned, would fall during sanitization periods, and that, because of comparatively rare presence of bird feeders in rural areas, rural birds may be relatively more impacted by the extent of feeder soiling
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