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

Abstract

Growing urbanization increasingly influences ecosystems worldwide. While the effects of urban conditions within species (through either plastic or evolutionary responses) have been widely studied, their potential influences among species (through environmental filter), especially concerning their colouration, remain poorly known. Here, we investigated whether avian communities breeding inside and outside a major European city (Paris) differ with regards to melanin‐based plumage colouration. Melanins are heritable pigments present in many taxa and have a series of unique properties that may allow coping with urban conditions. Using melanic‐based colouration as an integrative phenotypic marker, we predicted 1) that the probability of breeding inside the city should increase with the intensity of species melanin‐based colouration, 2) that for species breeding both inside and outside the city, density should increase with the intensity of dark colouration inside the city, but not outside the city and 3) that species not breeding inside the city should not exhibit this positive relation between density and colouration. Our results confirmed these predictions. In addition, the density of species not breeding inside the city decreased with the darkness of their plumage. Altogether, these results suggest that bird species experience a balance between costs and benefits of melanin‐based colouration shaped by environmental conditions. Both the environmental filtering and the urbanisation‐shaped relation between density and colouration evidenced here are likely a general trend, however possibly modulated by additional local environmental conditions. Their importance may even be underestimated given the restricted geographical scale and the overall urbanization rate of the region studied. Further studies involving regions with contrasted environmental conditions should gain insight into the consequences of urbanization worldwide on traits associated with melanin‐based colouration.

Urbanization as an environmental filter for megacolorful birds

“…Additionally, a recent study suggested that melanic birds (i.e. species with blackish colors) may thrive in urban assemblages due to the protective properties of melanin pigments, which can enhance resistance to tissue abrasion, higher temperatures, and detoxification of toxic metals commonly found in urban air pollution (Turak et al 2022). Megacolorful birds might thus not thrive in urban environments due to their low resistance to the damaging effects of urban pollution.…”

“…Estimates based on nighttime lights and artificial impervious areas show that urban land cover has increased over the last 30 years and now covers 0.5-0.7% (ca. 800,000 km 2 ) of the total land surface on Earth (Gong et al 2020, Zhao et al 2022. Moreover, global projections of urban land cover over the 21st century suggest that the total amount of urban land will further increase by a factor of 1.8-5.9, with the fastest urban land expansion occurring in the tropics (Seto et al 2012, Gao et al 2020).…”

Bird color and taxonomic diversity are negatively related to human disturbance in urban parks

“…Bird color diversity has recently been analyzed along urbanization gradients, and sites dominated by buildings were clustered compared to null models, being dominated by bird species with grey or dark colors (Leveau, 2019;Turak et al, 2022). Grey plumage may enhance bird camouflage with impervious grey surfaces (Leveau, 2019).…”