The Genetic Response of Forest Birds to Urbanization: Variability in the Populations of Great and Blue Tits

Anthropogenic pressures such as over-urbanization, intensive agriculture/forestry practices, and the development of energy farms alter natural landscapes. Intensive urban development poses the greatest threat to natural ecosystems. Habitat degradation, fragmentation, and loss are among the key factors behind the current rise of biodiversity loss. In this study, we hypothesized that urbanization advances the adaptation of forest bird populations to relatively new urban ecosystems. The study was conducted in Kaunas, Lithuania, located in Eastern Europe. Genetic samples were collected in the city, representing urban landscapes, and its surrounding forests. In total, 160 nest boxes were erected, of which 80 were placed in the urban areas and 80 in the forests. Using a set of microsatellite markers, we investigated the genetic differentiation, genetic diversity, gene flow, and population structure of two common forest bird species of the Paridae family, the great tit (Parus major) and blue tit (Cyanistes caeruleus), in forests and urbanized areas. We observed low but significant differences between urban and forest great tit and blue tit populations, proving relatively high population genetic diversity. We determined that cities’ spatial structure and fragmented natural habitats can influence the formation of small and isolated bird populations (subpopulations). Urban blue tits had higher genetic differentiation and a higher tendency to form subpopulations. In conclusion, forest birds can inhabit urbanized landscapes but both great tits and blue tits respond differently to urbanization-related changes.