Responses of avian guilds to urbanisation in a tropical city

Abstract

Avian ecology in tropical urban area is poorly understood. We determined, through surveys in 29 sites, how birds with different dietary and nesting requirements responded in terms of guild richness and abundance to various facets of urbanisation in Singapore. The sites selected were representative of the full range of urbanisation outside of the undisturbed native forests. Among the dietary guilds, we found that insectivores and carnivores were adversely affected by increased urbanisation. Frugivores were favoured by low-density housing, probably because more fruit-bearing ornamental plants were planted in such estates. Richness and abundance of shrub and shrub/tree nesters, and primary cavity excavators declined with increased urbanisation. We believe that the availability of nesting sites was an important factor in their decline. Exotic species accounted for only 13% of the total species richness detected in our surveys but they were numerically dominant (accounting for 61% of overall bird abundance). Abundance of native resident birds declined monotonically with increasing amount of built-up environment while birds of exotic species appeared to be more abundant in sites with intermediate amount of built-up environment. While urban greenery serves architectural and other functions, it has little effect on overall bird community assembly. The preponderance of exotic species in Singapore city suggests that birds of tropical rainforests are poor colonisers of this relatively novel environment. Many of the native urban species originated from mangrove and coastal scrub forests, so the maintenance of rainforests is necessary for the preservation of many native bird species.