Micro-scale patterns and drivers of bird visitation on street fig trees in Delhi, India

Abstract

Street trees have been used as a means of mitigating the negative effects of urbanization on biodiversity, particularly bird fauna. Despite their widely acknowledged benefits for birds, studies so far have been largely limited to relatively coarse scales, with an understanding of the role of local environments and individual tree characters lacking. We studied the patterns of bird visitation at individual street Ficus (fig) trees, providers of keystone resources in tropical landscapes, in Delhi, India, and their drivers at different scales (tree characteristics, local and landscape variables). Three common fig species were surveyed for bird visitors across 3 sites with varying urban patterns. Fig trees were found to be a relatively common street tree choice, and the 106 trees surveyed were visited by 29 bird species, including 7 obligate frugivores. We found that reducing green cover in surrounding landscape and increasing noise did not deter birds from visiting these trees. Instead, variables at finer scales like tree canopy diameter, tree species and local resource density had sizable and significant effects on both species richness and abundance of bird visitors. Our results highlight how bird assemblages, guilds and individual species respond differently to a range of ecological variables, and an understanding of these responses at different scales is useful for maximising the value of street trees for urban birds. Thus, coarse-scale studies can provide insights into bird diversity of city landscapes, but micro-scale studies are important in helping make fine scale management decisions, like selection of street trees.