Long-term dynamics of bird diversity in forest and suburb: decay, turnover or homogenization?

Aim Urbanization and deforestation are important drivers of biodiversity change. However, long-term changes in faunal communities within urbanizing regions are poorly understood. We investigated how well observed community changes in both space and time agree with expectations based on current paradigms in urban ecology. Location Greater Brisbane region, Australia. Methods We compared bird assemblages in two time-periods 15 years apart, at multiple sites in remnant forest and residential suburbs across an urbanizing landscape. Differences in assemblage composition, species abundances and functional groupings were assessed within and between habitats. Results Compared with forest, suburbs in both time-periods had over twice the total bird abundance, a different species composition, greater between-site community similarity, a greater proportion of non-native species and greater dominance by large-bodied species. These differences corresponded with changes in sites whose habitat was converted from forest to suburb. Between time-periods, abundances of 58% of suburban species changed significantly compared with those of 11% in forest. Increaser species outnumbered decreasers in suburbs, with the reverse in forest. Abundance of small-bodied birds decreased 70% in suburbs and 20% in forest. Broad-spectrum competitors and nest predators were common among suburban increasers. Among invasive species, the number of increasers was counterbalanced by decreasers. Both site-scale species richness and between-site community similarity increased to a small extent in both habitats. Main conclusions Species composition and ecological function of suburban bird communities were very dynamic. Suburban assemblages were neither a subset of forest species nor an increasingly non-native compilation. Communities in large forest patches were comparatively stable. The notion of habitat-specific species turnover better characterizes the nature of most changes than either species decline or homogenization, even though both of these were evident. There is considerable scope for careful urban planning, focused on both among- and within-habitat variety, to sustain bird diversity in urbanizing landscapes.