Environmental determinants of avian species richness in forests in a highly urbanized subtropical city: The effects of spatial scale and open space feature

Numerous avian studies have emphasized the importance of natural/semi-natural elements, especially green spaces to conserve avian diversity in a city. However, little is known about environmental factors associated with avian diversity in a densely populated and highly urbanized subtropical city where large scale of conservation management is not feasible. Using Macao as a case city, we investigated the relationship between environmental features and species richness of urban birds in forests at multiple scales. We analyzed point count data of birds collected at eight transects in five forests in Macao during 2007–2009. We divided survey periods into three seasons and considered them as temporal replicates. We calculated percent cover of each of two environmental features, i.e., open water (waterbody) and open green vegetation at three scales: 50 m, 250 m, and 500 m buffer areas surrounding transect. Rarefaction was used to estimate total richness (richness of all species) and richness of each guild (open habitat, shrub, and forest species). Total richness, open habitat species richness and forest species richness were affected by environmental features within the 250 m buffer area, whereas shrub species richness was not related with any scale. Percent cover of open water influenced positively open habitat and forest species richness and consequently total richness. Percent cover of open green vegetation had a positive effect on open habitat species richness but negative on forest species richness. These patterns were somewhat associated with vegetation features of forests. Our study indicates that even in highly developed small city, the relationship between environmental features and avian species richness can be influenced by spatial scale(s) at which these features are measured as well as species’ habitat preference. It also suggests that open features, especially open water could be an important factor affecting bird diversity in forests in urban areas.