By Patricia Waldron Feb. 14, 2017 , 7:15 PM
During their fall migration south, thousands of chimney swift birds (Chaetura pelagica) gather in a tornadolike flock at dusk before dropping down a chimney—five birds at a time—to roost for the night. But unlike European starlings, which form massive daily flocks called murmurations, chimney swifts are flocking amateurs that spend most of the year in small groups. To understand how the birds manage this complex and rapid descent, researchers focused three cameras on an 1800-strong flock of chimney swifts as they funneled into an industrial chimney in downtown Raleigh, North Carolina. By mapping the 3D position of each bird’s flight path, they found that swifts adjust their route based primarily on their closest flying neighbors, and ignore birds that are farther away, they report today in the Proceedings of the Royal Society B. Whereas the outer circling is neat and orderly, cooperation breaks down as birds near the chimney, and they make a dash for the opening to get the best roosting sites. On occasion, these rotating flocks will suddenly reverse direction midflight, or switch from flying in circles to figure-eight patterns, causing the birds to dodge each other. These “rules of the roost” could be used to program flocks of delivery drones to ensure a well-organized return to the warehouse, while avoiding expensive, midair collisions.