The influence of vegetation structure on bird guilds in an urban park

The acceleration of urbanization has led to a loss of biodiversity, which is a global ecological problem of great concern. Meanwhile, birds are useful indicators in monitoring environmental changes in urban ecosystem. Urban green areas have always been paid great attention because of their functions as natural habitats for many wildlife species. Bird guilds are groups of species that use environmental resources in similar ways. Therefore, we analyze the function of vegetation structure to bird community and bird guilds so that we make suggestions related to the design of urban green spaces in Shanghai. From October 2009 to October 2011, we set the line transect to survey the bird community in Shanghai Binjing Forest Park. According to the height of plant, we divided the habitat vegetation into three vertical levels including tree layer, shrub layer and ground layer. Chi- square test showed that there were significant differences among behaviors in three vegetation layers. The frequency of perching and moving in tree layer was more significant than that in other two layers and the frequency of feeding in ground layer was more significant than that in other two layers. According to the variables based on the location, feeding habits and foraging behavior pattern of birds, we classified 8 bird guilds including herbivorous collecting, herbivorous pecking, insectivorous collecting, insectivorous flying catching, insectivorous pecking, omnivorous collecting, omnivorous pecking and raptorial flying catching. There were differences and overlaps among the frequency of three behaviors of 8 bird guilds in three layers, so we considered there was niche overlap among 8 bird guilds. According to Morisita-Horn Index, the results indicated that insectivorous collecting guild, omnivorous collecting guild, flying catching guild and herbivorous collecting guild had high niche overlap of perching, and moving and feeding so these guilds reached niche separation by their diets. Insectivorous pecking guild and insectivorous flying catching guild had the most perching niche overlap with each other, and they reached niche separation by their foraging behavior patterns. Based on the results above, we concluded that trees were one of the most important vegetation components that enhance the bird species richness and diversity in urban green spaces because they provide roosting, nesting, hiding, and foraging sites. The shield function of shrub cover was confirmed to be an important habitat component and the ground layer provided food resources to bird community. The suggestion and recommendation in construction of urban parks was presented based on this study. The density and coverage of shrub layer should improve and large area of artificial lawn should be divided into several small pieces. We also discuss the conflicts between habitat for biodiversity maintenance and recreational function in urban parks.