Seasonality affects avian species distribution but not diversity and nestedness patterns in the urban parks of Vitoria–Gasteiz (Spain)

Abstract

Environmental seasonality leads to variation in the composition and structure of bird communities over the year that might alter biodiversity and nestedness patterns in urban parks and other frag-mented habitats. These changes could have important implications in the management and conservation of urban green areas and their populations, but they are largely unexplored. In this study, the composition, diversity and nestedness of the breeding and wintering avian communities in 31 urban parks of Vitoria–Gasteiz (Spain) were analysed. Avian diversity was significantly greater during breeding than during the winter period, although the most diverse parks during breeding were also the most diverse during winter. Most of the among–park variation in diversity was explained by park size, while tree density had a marginal contribution that was only significant during winter. Avian communities showed a significant nested subset pattern that was similar between seasons, with these patterns being mainly mediated by park size. Although the distribution of seven out of the 16 species occurring all–year–round changed significantly from one season to the other, the park ranks in the nestedness matrices were strongly correlated between seasons. This was caused by the reduction in the park distribution of some species from one season to the other that was compensated by the expansion of other species that were initially less common. These results support the idea that, in small and medium–sized cities, park size is the main constraint on avian diversity, and the presence of relatively large parks (> 10 ha) should be encouraged to promote a rich avifauna all year round.