Top ten birds indicators of high environmental quality in European cities

Urban and suburban areas are among the fastest-growing land-use types globally, reducing and fragmenting natural habitats for many animal species and making human-wildlife interactions more common. However, cities also create habitat for several species considered urban tolerant or urban exploiter species. Additionally, the environmental characteristics of urban areas can strongly affect the life quality of citizens. This study aimed to assess the effectiveness of common bird species as indicators of urban areas with high environmental quality within cities. Our study recorded 128 bird species in 1441 point counts distributed in fifteen different European cities. We classified urban areas as “high environmental quality” – HEQ when they were simultaneously characterized by a high vegetation cover and heterogeneity, low level of light pollution, and avian communities with high potential resilience to face ecological stress. Species indicators of HEQ urban areas were identified using the species-level indicator value (IndVal) analysis. Such species can be used as ecological indicators of HEQ in different European cities. The list of top ten birds indicators of HEQ in European cities is led by the Eurasian blackcap, selected as an indicator in more than half of the survey cities. Other birds indicators of HEQ in multiple cities are Blackbird (47%), Great tit (40%), Blue tit, Tree sparrow and Magpie (all 33%). The mean specificity of the top-ranked bird indicator of HEQ urban areas (Eurasian blackcap) was 0.778. Most of the HEQ-indicators are resident or resident/short migratory species characterized by territorial behaviour. Our findings support using multiple species as bioindicators of urban changes by using specific groups with few common species as surrogates of HEQ urban areas. The approach proposed in this study can be applied in different European cities to monitor biodiversity status periodically, even involving citizen science initiatives.