Does spring bring colors? Seasonal bird plumage color variation along urban-rural gradients

Abstract

Urbanization alters the landscape through the replacement of natural vegetation by impervious surfaces, probably inducing changes in interspecific bird color diversity and composition. However, the seasonal changes of bird color diversity and composition along urban-rural gradients have not been analyzed yet. The objective of this study was to analyze the seasonal variation of bird color diversity and composition of bird assemblages along urban-rural gradients of three cities in central Argentina. Bird surveys were made in urban, suburban and rural areas during the breeding and non-breeding seasons. Color description was obtained from the literature. Color diversity and the seasonal color dissimilarity were calculated using the mean pairwise distance functional index. Null models that control for species richness were used to estimate standardized effect sizes (SES). Color diversity increased during the breeding season. However, the SES of color diversity did not change between seasons. Color diversity and the SES of color diversity were higher in rural areas than in urban habitats. The color seasonal dissimilarity was the lowest in urban habitats. City size was negatively related to the color seasonal dissimilarity in urban and suburban habitats. Species with brown, black and dimorphic plumages showed seasonal changes in their abundances in rural habitats, whereas plumage colors in urban habitats remained stable between seasons. The results showed that bird color diversity increase during the breeding season, but this increase is related to the arrival of more species during the breeding season to rural areas. Urban areas showed a seasonal homogenization of bird colors.