Over 10 years ago while on a woodland hike with a friend in northwestern Pennsylvania, an intense low pitched pitter-patter sound from overhead startled us. Was it a sudden downpour on a sunny day? Through the foliage we caught a glimpse of hundreds of flying black birds. The sound faded then returned before it finally subsided. This flocking behavior remained a mystery to us but which we both recall to this day.

Today this flocking behavior we observed is recognized as murmuration, a massive flock of a single species of bird, the starling, sometimes approaching 10,000 in number. Thousands of flapping wings create an eerie murmur likely prompting the descriptive term murmuration. The flock passes back and forth over pastures and woodlots to roost for the night. While murmuration involves starlings, the behavior is similar to swarming of insects, like honeybees and locusts and schools of fish. The flock moves creating shapes resembling ellipses, dumbbells and columns while moving up, down, left and right. From a distance the flock looks like the rising material in a lava lamp. The flock may thin out, bunch up or sink, but remains a unit with sharp edges until ready to land. Biologists and physicists are searching for the mechanism which enables birds on one side of the flock to respond almost instantaneously to birds on the other side of the flock who suddenly change direction.

Numerous murmuration video images are available online by searching for “flocking of birds.” Just two weeks ago a murmuration over Gretna Green, Scotland, was selected as the Wall Street Journal photo of the week. Incidentally, the image captured a larger single bird to the right of the flock which my bird-watching friends think was a hawk in pursuit of the flock. Personally, I observed a small murmuration four weeks ago over pastures at the intersection of Riverside and Kiantone roads south of Jamestown. A small hawk, either a merlin falcon or Cooper’s hawk, was in pursuit of this flock. A friend in a group I meet with for breakfast described his observation this fall of a merlin diving into a murmuration only to miss a target, eventually leaving to hunt elsewhere.

European immigrants in the United States introduced 100 European starlings into Central Park in 1890-91. By 1950 starlings had spread to California. Today, the starling is thought of as mundane, a nuisance and an invasive species, but I bet the Europeans longed to see and hear a murmuration again, prompting them to bring starlings with them to America.

During the past 20 years, biologists, physicists and computer programmers have collaborated to discover how birds communicate within flocks. With use of stereographic cameras and statistical mechanisms the actions of 2,600 individual starlings have been observed on film at 10 frames/second. These studies reveal each bird is widely separated from each other. Each bird responds to only its closest six or seven neighbors, instead of a leader or coordinator bird. The trigger setting off a change in direction still remains a mystery, but theories suggest the presence of predators, brisk winds and noise created by turbulence from neighbor’s wing motion generates a brisk response to follow their neighbor.

Murmuration likely evolved for the success of the species. Biologists consider flocking to provide protection from predator birds because there is “safety in numbers” since attacking hawks invariably are distracted by numerous choices in a flock. When a single starling flies alone, hawks can concentrate, zeroing in to strike the individual. A second benefit to flocking before roosting may be the opportunity to socialize and communicate location of future feeding areas. After roosting at night starlings disperse often foraging 20 miles away. Thirdly, sitting close together on a roost after forming flocks may provide warmth at night.

This fall a murmuration may suddenly appear. You will be compelled to stop what you are doing to gaze at this unusual natural spectacle. In the meantime check out the images online to know what to expect.