Microhabitat coverage influences avian species composition more than habitat heterogeneity in Hong Kong urban parks

The relationship between habitat heterogeneity and diversity can underpin design of urban spaces for biodiversity conservation. The area-heterogeneity trade-off hypothesis predicts that higher habitat heterogeneity should result in an increase in species richness but only up to a point, beyond which habitat micro-fragmentation leads to decreases in species diversity. However, the strength of area-heterogeneity trade-offs at small spatial scales is not well studied. We studied the relationship between avian diversity and habitat heterogeneity in 16 small urban parks across Hong Kong during the winter dry season across 2016 and 2017 (ten repeated surveys in total for each park). Habitat heterogeneity was assessed by measuring the evenness of microhabitat coverage of seven habitats as well as vertical canopy cover. In total, 12,973 individuals of 73 bird species were recorded in the study. Habitat heterogeneity had a small but negligible effect on total bird species richness or abundance. However, water coverage was positively related to total, intermediately rare and habitat specialist bird species richness, and shrub coverage was positively related to total and common bird species richness. These results demonstrate that environmental heterogeneity had little effect on avian species richness in urban green spaces at small spatial scales. We also found that microhabitat coverage can affect avian diversity and abundance, and these effects are specific to certain groups of bird species. When managing urban green spaces for biodiversity conservation in densely urbanized cities, a decrease in management disturbance (e.g. tree topping or pesticide application) will likely benefit avian species. Together with the fact that some locally uncommon species were observed throughout the study, capacity exists for environmental enhancement of these small urban parks to contribute to local avian conservation.