Scientists analyzed 23 years of bird migration data collected via NOAA’s Next Generation Radar system — a network of 143 radar stations across the continental U.S. — to determine the variability in the birds’ arrival times each spring.

The Next Generation Weather Radar (NEXRAD) system is a network of 160 high-resolution S-band Doppler weather radars jointly operated by the National Weather Service (NWS), the Federal Aviation Administration (FAA), and the U.S. Air Force. The NEXRAD system detects precipitation and wind, and its data can be processed to map precipitation patterns and movement. NCEI provides access to archived NEXRAD Level-II data and Level-III products.