Why birds show up
A migrating songbird is roughly the size of a 5 cm water droplet — large enough to reflect S-band weather radar. At peak migration, dense flocks return enough energy to look like a light rainstorm. Dual-pol lets researchers tell birds from rain — the polarisation signature differs.
BirdCast and the AI layer
The Cornell Lab of Ornithology's BirdCast project runs ML models on live NEXRAD data, producing nightly migration maps and 3-day forecasts. Cities use these forecasts to dim skyscraper lights on high-migration nights, cutting bird collisions by an estimated 60–80%.
What it tells us about climate
Long radar archives — 25+ years — show that some species are migrating up to 2 weeks earlier than in the 1990s. This is one of the most precise climate-impact datasets in biology, and it comes from machines designed to track thunderstorms.
DIY radar ornithology
Anyone can download Level II NEXRAD data, run it through open tools like wsrlib or BirdCast viewers, and observe roost rings forming at sunrise around lakes and swamps. It is a strange and beautiful side door into ecology.