Long-term shifts in a suburban bird community

Long-term data on changes in avian diversity from urban habitats are essential to address the ongoing declines in European bird populations. We aimed to analyse historical changes in the bird assemblage of an urban district of Bonn, Germany, over 50 years. We surveyed the breeding bird population in a district of Bonn, Germany, and compared our results in terms of species richness, abundance, habitat type, and biomass with results from a survey conducted exactly 50 years earlier. To compare changes in habitat composition we analysed historical and current aerial photos.

Between surveys, there was a severe decline in species richness and a strong homogenization of the bird assemblage while the overall number of breeding birds slightly increased. Biomass increased but was strongly influenced by the massive increase of the Common Woodpigeon Columba palumbus. Many forest species that rely on older trees increased in abundance while the typical species of settlements and open habitats strongly decreased. However, large-scale habitat changes are not sufficient to explain these patterns.

Urbanization of Central European cities has boosted populations of generalist species while those already of conservation concern will further decline if their demands are not considered in current urban planning approaches. Our work highlights that historical data on breeding bird abundance are of high importance and should be sought and used. In our case such data demonstrated the impact of small-scale changes in habitat and other parameters highlighting that these should receive more attention.