Seasonal fluctuations of urban birds and their responses to immigration: An example from Macau, China

Abstract

Understanding interactions between resident and non-resident birds in urban areas is important for managing urban greenspace to protect urban bird diversity. Here, we determined how interactions between resident and non-resident species potentially affect bird diversity in the urban green species of Macau (subtropical area of China). We examined seasonal fluctuations in the habitat use and structuring of an avian community, along with potential drivers. We recorded habitat use relative to land-use/landcover configurations, focal habitat characteristics, and disturbance data in 13 semi-isolated urban parks to identify factors driving competition. We used line-transects to count individual birds and species, and analyzed the data using ANOVA, linear regression, and variance partitioning analysis. Species richness, the abundance of non-residents, and the population size of various resident feeding guilds noticeably fluctuated across seasons within the year. These phenomena were attributed to birds migrating through Macau during spring and fall, which drove structural changes to resident bird populations. Resident and non-resident insectivore and insectivore-frugivore populations responded positively to shrub cover in spring, and to proximity to large waterbodies in fall. However, while both resident insectivores and insectivore-frugivores utilized high quality habitat during summer (non-migratory season), when interspecific competition was low, these two groups competed for available habitat during the migratory seasons. Thus, resident and non-resident bird guilds appear to compete for optimal habitat in Macau during the migratory seasons. In particular, residents appeared to avoid direct competition with migrants, potentially associated with the trade-off between fitness costs and shifting patches. Our results provide new insights on the seasonal fluctuations in the community structure of urban birds and potential driving factors. By understanding how the importance of certain habitats changes with changing community dynamics, the management of urban green spaces could be guided to ensure certain habitat types are more available.