Concrete Habitat Severely Decreases the Reproductive Output of Two Urban Birds

The conversion of natural habitats to impervious surfaces in cities affects biotic and abiotic attributes of urban ecosystems. However, detailed information on the gradual influence of impervious surfaces on reproductive output is lacking. Using 5 years of nestbox-breeding great tit and blue tit data collected across various habitat types within and outside a Central–Eastern European capital city, we quantified the impact of impervious surfaces on avian reproductive success. Impervious surfaces strongly and negatively covaried with the number of fledged young in both species: a 0%–50% increase in impervious surface within 100 m of the nest was associated with 3.56 fewer fledged offspring in great tits (95% CI: −4.85, −2.27) and 2.91 fewer fledged offspring in blue tits (95% CI: −4.26, −1.56), thus halving the reproductive output of two widespread urban species. These results provide benchmark values of avian productivity for ecologists and urban policy makers, and for the management of urban areas.