Decadal changes in urban bird abundance in Singapore

Abstract

Birds are one of the most cost-effective groups to survey for monitoring human impacts on faunal communities and are consequently the best studied taxonomic group in urban areas. Urban bird assemblages are typically dominated by a few pest species, and need to be appropriately managed to reduce the aesthetic costs and health risks they may pose in highly-populated areas. Studies were conducted in Singapore (Feb.2000 to Feb.2001) to provide recommendations to manage urban birds, in particular to control the population of two invasive alien bird species: the house crow (Corvus splendens) and the Javan myna (Acridotheres javanicus). We then re-surveyed the same sites 9 years later (Mar.2010 to Feb.2011) to compare the changes in the abundance of the 20 most common urban bird species in Singapore over the past decade. We also tested whether the decrease in house crow abundance was correlated with increases in abundance of its co-invasive, the Javan myna, or with the Asian koel (Eudynamys scolopacea), a brood parasite of the house crow, across sites. In addition, we investigated competition between two myna species by comparing whether declines in the abundance of the common myna (Acridotheres trista) were correlated with increases in the abundance of the Javan myna. Our results showed that a total of 14 species recorded a signifi cant increase in abundance between the two surveys, two species signifi cantly decreased, and four species had no signifi cant change. There was also no signifi cant correlation between all the bird abundances, although changes in bird abundances were signifi cantly associated with certain changes in the urban environment such as spontaneous or cultivated green cover. We suggest that reduced density of house crow nests may actually result in increased vulnerability to, and hence success rate of, brood parasitism by the Asian koel, or there may be increased parasitism of other host species' nests. Meanwhile, competitive effects among the other birds may not be detectable at the scale of the transects used in our study. © National University of Singapore.