Urbanization and bird diversity: does the relationship change in deserts and subtropical forests?

The relationship between urbanization and different bird diversity facets, such as taxonomic and functional diversity, may depend on the biome where cities are located. We analyzed the impact of urbanization on bird taxonomic and functional diversity in two contrasting biomes of Argentina: desert and subtropical forests. A total of five cities and five natural areas were surveyed in each biome during the breeding season. Taxonomic diversity was measured as the bird species richness in each sampling unit, whereas functional diversity was compared with null models that controlled for differences in species richness. Taxonomic diversity increased in periurban areas located in the desert and in natural areas of forests. Natural areas of the desert biome had similar functional diversity to that of urban areas, whereas natural areas of the forest biome had lower functional diversity than expected for a given number of species. Urban core areas in both biomes were dominated by species that eat seeds and plant materials, and by ground foragers. Natural areas in both biomes were dominated by species that eat invertebrates, and by understory and midstory foragers. Our results showed contrasting relationships between different bird diversity facets and urbanization in desert and forest biomes. Moreover, the results found highlighted the importance of considering different urban habitats in large-scale comparisons and the need for particular management actions in different biomes.