Artificial light in cities exerts negative effects on humans, animals, and their environment. In an ongoing research project, behavioral biologists at Vetmeduni Vienna are investigating how blue tits in the Viennese Forests react to "light pollution". The study might help to understand effects of “light-at-night” on reproductive behavior of birds. In consequence, it could help developing concepts, minimizing negative effects on the lives of animals and the ecological system, by reducing light sources in specific regions. The research project started this year and is supported by the city of Vienna.