Urbanization does not affect green space bird species richness in a mid-sized city

Urbanization is one of the most intensive forms of landscape and habitat transformation, resulting in species loss, and taxonomic and functional homogenization of different communities. Whilst green infrastructure (the network of natural and semi-natural areas in cities) has been studied extensively in terms of specific features that promote biodiversity, there have been no studies that have assessed how species richness in different types of green space (GS) varies with increasing levels of urbanization in the surrounding matrix. We studied the effects of different types of GS and urbanization in the surrounding matrix on bird communities in the mid-sized city of Göttingen, Germany. We used the point-count method for bird observations in allotments and parks. To determine the level of urbanization, we calculated percentage of impervious surfaces around GSs. Increasing levels of urbanization around GSs had no effect on the species richness, functional traits or the community composition of birds. Nevertheless, we found that species richness and functional traits varied according to GS type. Parks had a greater species richness and were found to have more ground nesting and tropical migrant birds compared to allotments. We found more cavity nesting and resident birds in allotments. As different types of GS can contribute to the presence of different species and functional trait variations, their positive effect on bird species richness can be enhanced when they are present together in urban landscapes. Our findings suggest that green spaces with a high variety of local characteristics should be incorporated into urban planning designs in order to ensure diverse bird communities in cities.