Threshold distances to nearby cities and roads influence the bird community of a mosaic landscape

Urban developments and road networks extend their impacts on the surrounding habitats along a variable distance, affecting birds living in natural environments. This study identifies the threshold distances upon which several cities and roads, located across a large mosaic landscape of ca. 300 km2 in central Spain, alter the abundance patterns of the native avifauna. Total species richness, total bird abundance, and abundance of different guilds of birds which are potentially sensitive to human disturbances were modelled by means of tree regression analyzes. Nearby cities do not affect the total bird species richness in natural habitats of the study region. Total bird abundance increases near urban areas, mainly through its positive influence on urban-exploiter species. The effect of roads is negative and highly generalized, although threshold distances to roads vary among different groups of species. The bird communities of deciduous woodlands (ash groves, oak patches and poplars) show higher resilience to deletereous influences from nearby cities and roads. It would be desirable not to build new scattered urban developments within the remnant natural areas of this heavily fragmented region, because their existence and connection to the nearby cities by new roads would add ‘invisible’ negative effects on the native bird fauna (e.g. on some threatened species from open habitats), considering the buffer distances determining most significant impacts (400 m for urban areas, and 300 m for roads).