Effects of the features of contemporary occidental cities on urban avifauna

Since the first permanent human settlements in the Holocene, 10 000 years ago, until contemporary cities birds have cohabited with humans. In the last decades, urbanization has grown exponentially on the planet and in 2030 the 60% of the world population will live in urban areas. Based on their urbanization tolerance birds are classified into three categories: urban avoiders, adapters, or exploiters. Current occidental cities attract birds due to the presence of abundant and predictable trophic resources, reduction of predators' diversity, or the existence of nesting places, among other factors. However, urbanization is nowadays one of the greatest problems for biodiversity and the model of a contemporary city may become unattractive to birds and indeed some urban species are declining in the present. Some reasons that explain this process are loss of green areas, pollution, changes in abundance and composition of trophic resources, and new building trends. Changing the model of a contemporary city to protect biodiversity is a difficult challenge but it is possible and there exist inspiring experiences like the green infrastructure of the city of Vitoria-Gasteiz (Spain).