By Tyler Pruett
RAINSVILLE, Ala. — On Sunday, July 31, a series of unusual radar signatures appeared over several areas of North Alabama and Tennessee on WHNT 19’s weather radar. The patterns were in a ring shape, and disappeared shortly after popping up even though the skies were clear and no precipitation was in the area.
The patterns appeared over Winchester (TN), West Decatur, Huntsville, and Rainsville. While military tests at Redstone Arsenal have been known to occasionally create strange radar signatures in the past, the cause of this anomaly was something completely different.
The large rings were apparently caused by large group of birds common to Alabama and most of the Eastern United States. According to WHNT 19 meteorologist Christina Edwards, the rings were caused by Purple Martins leaving their roosts in large numbers.
The species typically live in colonies, and usually take up residence in crevices; either natural or man-made. Many people in rural areas hang hollowed-out gourds to create a habitat for the birds; believing that they help control the insect population. However, the birds find the best roosting environment in urban areas, where small crevices on buildings and overpasses make a perfect habitat.
The martins generally leave their roost at the same time, creating a “cloud” on the radar over areas where there are large concentrations of the birds. According to Edwards, these patterns can sometimes reach 60 miles across.
"In addition to birds, weather radars can also detect bats, bugs, buildings, trees, and even trucks as they head down the highway. This is why you can see ‘green’ on a radar, even when no rain is available to produce a signal," Edwards wrote in her blog.
Although there are currently enough Martins in the area to create a “cloud” on the weather radar, the small birds aren’t around during the winter. According to wikipedia.com, Martins migrate all the way to the Amazon Basin in South America during the winter months, and move back to North America in the spring to breed.
Martins have always had a close relationship with humans, and live in close proximity. Putting up gourds to create habitats for the birds predates the settlement of America, with Native Americans starting the practice.