Weather radars see birds as well as rain. Aloft publishes the bird density profile each European radar retrieves every few minutes; this map integrates those profiles into a column total and interpolates between stations.

Insects, rain and ground clutter contaminate the retrieval, and coverage is far denser in the Low Countries than in Iberia or the Balkans — where the network thins out, so does the colour.

Data: aloftdata.eu (ENRAM, CC0). Times are UTC.