Thermo-modernization influences nest density of Common Swifts (Apus apus): determinants of nest site choices in Poznań, Poland

At present rate of urbanization, it is particularly relevant to recognize the importance of urban species conservation. The Common Swift is highly adapted to urban conditions, with possibilities of ecosystem service provision. The aim of this study is to improve swift conservation via determining factors important in nest site choice, and colony density, with special attention to contemporary changes. The results of our study may be applicable for other cities and other urban bird species. A detailed survey was carried out in swift nesting sites in the old part of Poznan, Poland. To obtain information on spontaneous nesting site choices, we compared nesting sites to randomly assigned points within the same area (i) and assessed the drivers of nest aggregation tendency (ii). We used generalized linear models and random forest algorithms, to answer which habitat and nest site characteristics influence the occurrence and size of swift colonies. 387 swift nests were found (43.6 pairs/10 hectares). Swifts avoided areas with high green cover, preferred relatively high buildings, which were built before 1939, and avoided high car traffic. Larger groups of nests were found on areas, with a higher proportion of buildings lacking thermo-modernization (insulation during the last 10 years), despite extreme sun exposure. Although current legislation is in favor of species protection, we indicated some legislative pitfalls, mainly related to thermo-modernization. There is a need for careful assessment of all funding programs to achieve a win–win in terms of climate-change adaptation and urban species conservation.