Influence of habitat urbanisation on time of breeding and productivity of Tawny Owl (Strix aluco)

An increasing urbanization of habitats in which birds live influences their populations by modifying behaviour, dietary composition, causes of mortality and variables related to breeding. This study aimed to compare breeding periods and productivity among tawny owls, Strix aluco, inhabiting either an urban or an extra-urban area. Studies were conducted in parallel in two locations: central zone of Warsaw – the Polish capital – and the Rogów Forest – ca 70 km west of Warsaw. Number of fledglings and the beginning of the breeding period was assessed by direct observations and listening to calls of juveniles within tawny owl territories. Birds in the urban area were found to start breeding significantly earlier (from 5th February) than those in the extra-urban area (from 17th March). However, the two populations proved to be similarly productive, with 3.2 or 3.4 young per nest on average. The phenomenon of early breeding in city dwelling birds was confirmed in other tawny owl populations as well as other bird species. It can be potentially driven by factors such as higher temperature, artificial light and rich and stable food base.