Bird-feeder cleaning lowers disease severity in rural but not urban birds

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.

Effects of urban sugar water feeding on bird body condition and avian diseases

“…This is the first study to report avian infections and body condition indices for species associated explicitly with sugar water feeding. 23,39,40 Our finding of higher prevalence of coccidia infection associated with sugar water feeding in one species, tauhou, is likely linked to the clustering of this nectarivorous bird around feeders, which does not happen in non-feeding gardens.…”

“…and coccidia infections at feeding stations where feces accumulation was prevented by regular cleaning. 23,82 Does sugar water feeding pose a risk to native birds?. Although there was no evidence of highly pathogenic Salmonella spp.…”

“…[14][15][16][17][18][19][20][21][22] In particular, more frequent feeder visits can lead to increased transmission of avian viruses and ectoparasites through direct body contact, and gastrointestinal parasites through accumulation of contaminated feces. 4,6,15,[22][23][24][25][26][27] There is also the potential for Salmonella enterica, the agent of salmonellosis infection, transmission to humans via bird feeding. 10,21,28 Other infections associated with bird feeding can cause considerable avian mortality leading to downstream impacts on urban ecosystems since birds provide many ecosystem services and feature in human recreational activities.…”

“…[29][30][31] Bread and seed are the most commonly offered supplementary foods, 3,32,33 and the most studied context for examining how supplementary feeding contributes to avian pathogen prevalence. 23,24 Avian diseases in species associated with grain-based feeders include coccidiosis, 34 trichomoniasis, 19,35 mycoplasmal conjunctivitis, 17,36,37 chlamydiosis, 38 and avian poxvirus (Lawson et al, 2014). Meat-based feeders for red kites (Milvus milvus) have been linked to a higher prevalence of endoparasites (coccidia and helminths) in birds at feeders, compared to conspecifics consuming primarily wild prey.…”

“…Despite its popularity in many countries where nectarivorous bird assemblages are part of urban ecosystems, information on pathogen and parasite prevalence associated with sugar water feeding is lacking. 23,39,40 One of the main concerns is that this carbohydrate media is highly suitable for bacterial growth, especially in hot climates or warmer seasons. 41,42 In addition, the low concentrations of sugar solution usually used for bird feeding [43][44][45] have been shown to stimulate bacterial and yeast growth.…”