How to read this for birds

• A bright donut 20–60 km out from the radar, blooming ~30 min after sunset, is the liftoff signature — millions of wings climbing through the beam at once.
• A concentric ring that expands and fades around dawn is the descent — birds dropping into woodlots, beaches, and parks like Wendy.
• Smooth 5–20 dBZ wash (blue / green / yellow) is biology — birds, bats, insects. Splotchy high-dBZ blobs that move with the wind are precipitation and usually kill the migration window.