Watch thousands of birds fly in tight formation—a mesmerizing behavior known as a starling murmuration. | National Geographic

SEE IT: What looks like a giant school of fish flying across the sky is actually a phenomenon called "murmuration." Murmurations occur when a flock of starlings (small birds) produce a synchronized cloud of movement over their chosen roost site. A roost is where they will rest as a group for the night, which is why murmurations occur most often at sundown. People gathered in the town of Tewkesbury in England to watch this starling murmuration on Saturday, Jan. 28. Tewkesbury became a hotspot for