Large-scale citizen science survey of a common nocturnal raptor: urbanization and weather conditions influence the occupancy and detectability of the Tawny Owl Strix aluco

Abstract

ABSTRACT Capsule Tawny Owl Strix aluco site occupancy and detectability are influenced by habitat and environmental variables. Aims: To determine factors influencing Tawny Owl occupancy and detectability around British homes and gardens using a large-scale citizen science survey across two main survey periods. Methods Surveys of 20 min duration were undertaken one evening a week from the homes and gardens of volunteers, for up to 26 weeks between October and March of 2005/2006 and 2018/2019, and analysed primarily using multi-season occupancy modelling. Results During two survey periods, more than 9000 sites were surveyed across the breeding range of the Tawny Owl within Britain. The main drivers of occupancy were found to be the extent of broadleaf woodland cover and the degree of urbanization. Detection probability was influenced by date, time, weather, and moon phase. Using the current method, a minimum of five to six survey visits per site would be required to have 95% confidence over the presence or absence of Tawny Owls at a given site, but it may be possible to optimize the survey method further to increase efficiency by surveying in the autumn or early spring, early after dusk, and on cloudless dry evenings close to the full moon. Conclusion The findings indicate that survey methodologies for surveying Tawny Owls can be optimized to increase the efficiency of detection, if present at a site. We highlight the need for further research on the effects of urbanization on Tawny Owls, particularly with regards to artificial light pollution and its effects on behaviour and settlement, along with the need for greater understanding of Tawny Owl activity budgets, which would aid the interpretation of survey results.