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

Abstract

Recently, studies have shown that highly urbanized areas are numerically dominated by birds with grey plumage, probably favoring camouflage with impervious grey surfaces. However, patterns of bird color diversity in urban green areas remain unexplored. In urban parks, sites surrounded by highly urbanized areas may be dominated by grey bird species, whereas urban parks with pedestrians that feed birds may favor commensal birds which also have grey plumage. Thus, we explore the relationship between environmental variables and bird taxonomic and color diversity in urban parks. Bird surveys were conducted twice by fixed points in urban parks of six cities in central Argentina. Bird color diversity was assessed by characterizing bird plumage coloration in different parts of the bird body and the presence of plumage sexual dimorphism, polymorphism, and iridescence. Then, color richness and color diversity (abundance-based) were calculated with species mean pairwise distance. Null models were used to quantify richness-corrected color diversity. Bird species richness and diversity increased with green-area size, and bird diversity decreased with increasing pedestrian traffic. Color richness decreased with increasing car traffic, whereas color diversity was positively related to green-area size and negatively related to car and pedestrian traffic. Richness-corrected color diversity related negatively to car and pedestrian traffic. The abundance of grey birds increased in parks near the urban centers and related positively to pedestrian and car traffic. The abundance of yellow birds increased in parks near rural areas or small cities. Color diversity increased with green-area size, but richness-corrected color diversity ceased to be related to area size. Therefore, the increase in color diversity with area size was mediated by increases in species richness. Color diversity was clustered in parks with the highest human disturbance, favoring the abundance of grey species which probably took advantage of food discarded by humans.