What looked like light rain sweeping across the Tampa Bay area early Monday morning was actually something else entirely: millions of birds in flight. Max Defender 8 radar picked up the signal during peak fall migration, and meteorologists determined the reflectivity values were showing migrating birds rather than precipitation.
According to WFLA, more than 55 million birds crossed Florida overnight during peak fall migration. The station’s meteorologists used the correlation coefficient tool on dual-polarization radar to distinguish the biological scatter from actual precipitation, since the coefficient measures how consistent object sizes are within the radar beam and flags lower consistency as nonmeteorological material. That same tool is typically used to spot flying debris from severe storms and tornadoes, but it can also reveal biological scatter from bugs, bats, and birds, the station’s report notes.
BirdCast also estimated that more than 55 million birds crossed Florida overnight. In Hillsborough County specifically, BirdCast estimated that roughly 6.7 million birds crossed overnight, with local flight traffic peaking at about 2.8 million birds aloft at once at an average altitude of 2,400 feet.
Why the Signal Shows Up Only After Dark
The reason Tampa’s radar caught a migration bloom overnight rather than during the day comes down to bird behavior. More than 80 percent of migratory bird species in North America fly nocturnal routes, typically departing 30 to 45 minutes after sunset and reaching peak flight density two to three hours into the night, according to the Cornell Lab of Ornithology. Flying at night lets small songbirds avoid daytime predators while taking advantage of cooler air and calmer atmospheric conditions…