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Migration in an illuminated world

Examining responses of migratory birds to artificial light at night

Artificial light at night (ALAN) is a global stressor for migratory species. To reduce its impact, we must understand the effects of light on birds, and how they can be minimized by compromising human habits. We use radar and tracking technology in a European region where light effects can be identified. After crossing the dark Adriatic Sea, spring migrants encounter patches of light and darkness at the Croatian coast. We examine how the birds’ behaviour differs when exposed to dark or illuminated areas. Then, we will test experimentally how these differences can be reduced by modifying light.

Domain Research
Unit Bird Migration
Topic Birds and Human Beings, Ecology, Migratory Birds
Habitat alpine habitats, farmland, forest, meadows and pastures, rivers & streams, rocky terrain, semi-open farmland, settlements, wasteland, wetlands
Project start 2022
Project completion 2026
Project status ongoing
Project management Baptiste Schmid
Project region Europe


Project objectives

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.


The project is at its beginning. Currently, radars and sound recorders are deployed (see Gallery) and collect data.

Project partner(s)



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Bird Migration

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