Examining responses of migratory birds to artificial light at night

Millions of migratory birds die each year because of attraction to light followed by collision. Many more deviate from their routes because of ALAN. We aim to investigate migration under ALAN at multiple scales, from aerial flow of birds to their individual behaviour. The project will quantify ALAN effects on the flight behaviour, route and stop-over locations of avian migrants, and also carry out experimental work. We aim at improving knowledge for evidence-based mitigation of ALAN through light pollution guidelines of the CMS (Bonn Convention).

We use radar technologies to investigate the influence of environmental and experimental ALAN on migration intensity, flight direction and speed. Two pairs of radars are placed at nearby dark and brights locations along the Croatian coast. We seek to identify species that contribute to the ALAN response by parallel acoustic monitoring of flight calls. Lastly, we use tracking technology to study the movement of individuals across the local nocturnal lightscape to infer behavioural decisions.

A recent study of citizen scientists and Vogelwarte has revealed the extent of ALAN-induced mortality of migratory birds (see Gallery). Unlike many other forms of human pollution, light pollution can be immediately undone if we change our lighting habits. Turning off the lights at night is ideal, but often humans feel they require night lights. In this situation, we need to understand how birds respond to ALAN during migration, and which light features have the strongest effects. Then, we can reduce our impact by choosing the least harmful light for human purposes.

We have so far collected radar data from two spring migration seasons and have retrieved the first migration tracks from Scops owls (see Gallery).

• Simon Hirschhofer, University of Zürich
• Robert Weibel, University of Zürich
• Peter Ranacher, University of Zürich
• Sanja Barišić, Institute of Ornithology (HAZU), Croatian Academy of Sciences and Arts, Zagreb, Croatia
• Davor Ćiković, Institute of Ornithology (HAZU), Croatian Academy of Sciences and Arts, Zagreb, Croatia
• Maja Bjelić
• Louie Taylor
• Barbara Vodaric Surija, Croatian meteorological Office
• Carles Vilà, Spanish National Research Council, Spain
• Alberto Benito Ruiz, Spanish Ornithological Society, Santander, Spain
• Ignacio Fernandez Calvo, Spanish Ornithological Society, Santander, Spain
• Felipe González Sánchez, Spanish Ornithological Society, Santander, Spain
• Jesús Avilés, Spanish National Research Council, Spain
• Deseada Parejo, Spanish National Research Council, Spain

• European Commission (Horizon Europe): MSCA Postdoctoral Fellowships