Plumage micro-organisms and preen gland size in an urbanizing context

Abstract

Urbanization of Earth's habitats has led to considerable loss of biodiversity, but the driving ecological mechanism(s) are not always clear. Vertebrates like birds typically experience urban alterations to diet, habitat availability, and levels of predation or competition, but may also be exposed to greater or more pathogenic communities of microbes. Birds have been popular subjects of urban ecological research but, to our knowledge, no study has assessed how urban conditions influence the microbial communities on bird plumage. Birds carry a large variety of microorganisms on their plumage and some of them have the capacity to degrade feather keratin and alter plumage integrity. To limit the negative effects of these feather-degrading bacteria, birds coat their feathers with preen gland secretions containing antibacterial substances. Here we examined urban-rural variation in feather microbial abundance and preen gland size in house finches (Haemorhous mexicanus). We found that, although urban and rural finches carry similar total-cultivable microbial loads on their plumage, the abundance of feather-degrading bacteria was on average three times higher on the plumage of urban birds. We also found an increase in preen gland size along the gradient of urbanization, suggesting that urban birds may coat their feathers with more preen oil to limit the growth or activity of feather-degrading microbes. Given that greater investment in preening is traded-off against other immunological defenses and that feather-degrading bacteria can alter key processes like thermoregulation, aerodynamics, and coloration, our findings highlight the importance of plumage microbes and microbial defenses on the ecology of urban birds.

Plumage iridescence is associated with distinct feather microbiota in a tropical passerine

“…In other avian species, studies have documented that preening behavior can significantly reduce feather microbial load 38,82 , enhance feather condition including waterproofness 83 , or increase feather visual signaling properties 84,85 . There is also evidence for associations between degree of feather microbial load and preen gland size 86–88 supporting significant role of preen gland and its secretions in alterations of feather microbiota. Furthermore, allopreening (e.g.…”

A review of urban impacts on avian life‐history evolution: Does city living lead to slower pace of life?

“…The results on studies analysing immunocompetence depend on the immune trait that is studied (Table 2). Urban birds have larger preens (Giraudeau, Mckenna, Hutton, & Mcgraw, 2016), larger swelling response to phytohemagglutinin injection (Audet, Ducatez, & Lefebvre, 2016), and more heterophils and eosinophils (Fokidis, Greiner, & Deviche, 2008). At the same time, lymphocyte count seems to be lower in urban birds (Fokidis et al, 2008).…”

Urbanization shapes the relation between density and melanin‐based colouration in bird communities

“…At the intraspecific level, polymorphic species (insects, birds, reptiles) tend to be more melanic in urban areas, possibly due to camouflage, to resistance to parasitism (Jacquin et al 2013), to stress response (Corbel et al 2016), to metal detoxification (Chatelain et al 2014(Chatelain et al , 2016 and perhaps to resistance to feather-degrading bacteria (Gunderson 2008, Azcárate-García et al 2020) and parasites, more abundant in the cities (Giraudeau et al 2014(Giraudeau et al , 2016. At the interspecific level, some of the factors previously proposed for the increasing proportion of melanic individuals along urbanization within species may also be involved in the urban-associated costs-benefits balance of melanic colouration among species.…”