The more urban spaces are covered in concrete, the fewer birds successfully raise their young. A new study led by Prof. Marta Szulkin from the Faculty of Biology at the University of Warsaw not only confirms this link but also provides precise data that policymakers can use. The findings were recently published in Conservation Letters.

The study, published in Conservation Letters, presents clear evidence that increasing the proportion of impervious surfaces—such as concrete and asphalt—leads to a decline in the breeding success of urban birds. When half of a biologically active area is replaced by built-up surfaces, the number of chicks successfully leaving the nest drops roughly by 50%.

“As cities expand rapidly, decision-makers need hard data to support urban planning that includes green infrastructure. Our study provides urban planners, landscape architects, and policymakers with the information necessary to design bird-friendly spaces. It also quantifies how a systematic increase in concrete and asphalt directly reduces the number of fledglings leaving nest boxes,” explains Prof. Marta Szulkin.

Pioneering Research in Central and Eastern Europe

Prof. Szulkin highlights that this is one of the first large-scale studies of its kind conducted in Central and Eastern European cities.

“Although we analyzed five years of data for this publication, our research is the culmination of a decade of work in Poland. Over the years, we have established a network of over 500 nestboxes in Warsaw and the surrounding areas,” says Prof. Szulkin.

The nest boxes were installed not only in parks but also in residential, cemeteries, and both urban and suburban forests. Some were also placed on the Ochota Campus of the University of Warsaw.

Importantly, the study provides much-needed estimates East of the Iron Curtain—an essential step toward a more complete understanding of how urbanization impacts wildlife.  Historically, most urban ecology studies have focused on cities in Western Europe and North America. Expanding research to Central and Eastern Europe, as well as Global South and Majority World cities, is critical for building a truly global picture of biodiversity loss and resilience in urban environments.

The study presents detailed estimates for two common tit species: the great tit (Parus major) and the blue tit (Cyanistes caeruleus). Each year, researchers monitored the birds for several weeks in early spring. Many PhD students contributed to the fieldwork, with the paper’s first author being Dr. Michela Corsini, a former PhD student of Prof. Szulkin.

Key Findings

• The loss of vegetation and natural nesting sites in highly urbanized areas is an increasing challenge for urban wildlife.
• Bird breeding success declines as the proportion of impervious surfaces increases. When 50% of green areas are replaced with concrete, the number of fledglings per nest box drops by half.
• The findings provide urban planners with guidelines for designing green spaces that better support urban bird populations.