Sometime in late October or early November I hear and then see enormous blackbird flocks as they briefly land in our forest calling and feeding. Usually they consist of incredibly noisy European starlings and common grackles on their way South for the winter. I enjoy watching and listening to them as they engage in what scientists call “cluster flocking” or “collective animal behavior,” terms which include schools of fish, swarms of insects, flocks of birds, and herds of mammals.
But none are more spectacular that the murmuration flights of European starlings, described by Grainger Hunt, a senior scientist at The Peregrine Fund, as “a dazzling cloud, swirling, pulsating, drawing together to the thinnest waist, then wildly twisting in pulses of enlargement and diminution, a fluid choreography of funnels, ribbons, and hourglasses, spills and mixing, ever in motion.”
European starlings are an invasive species, brought over from England in 1880 by well-meaning Shakespeare enthusiasts who wanted to fill American skies with every bird species mentioned by the bard. But many Americans regard them as pests. In contrast, Europeans have appreciated murmurations for a very long time. And judging by the popular You Tube murmuration video shot over the River Shannon in Ireland, not only Europeans but Americans and nature appreciators throughout the world have been wowed by the phenomenon.
Even bird-oriented magazines such as Living Bird and Audubon have featured stories and photos of murmurations, although the latter was taken to task by one reader for glorifying the invasive species, admitting that the photos were “spectacular” but the birds themselves “a scourge,” that had perpetrated “extreme damage on North American ecosystems…”
That may be true but everyone from poets to the publisher of The Christian Century have been inspired by murmurations they have witnessed in the United States. Poet Barbara Crooker in her poem “Murmuration” describes “the gray silk sky embroidered with black kisses” and “an immense river of noise.” That noise, produced by multiple wingbeats, is why the phenomenon is called a “murmuration.”
Publisher Peter W. Marty writes that their “synchronized movements look like a magic carpet rippling and rolling through the sky” and remind him of the musical term “legato,” because it “has a curved line above the phrase to indicate that it is to be sung or played in a flowing manner.”
Scientists too have been intrigued and puzzled by starling murmuration. Dozens and dozens of papers have been written speculating on the how and why of murmuration beginning with the British naturalist Edmund Selous who, in his 1905 paper, called it “a madness in the sky.” After 30 years of studying murmuration and other flocking by birds, he thought that only the threat from a predator, such as a peregrine falcon, or “a kind of telepathy between the birds,” what he called “thought transference” could be responsible.
Another scientist, Wayne Potts, a biologist at Utah State University, came up with what he called “The Chorus Line Hypothesis” by filming the so-called “dance of the dunlins,” which is similar to the murmuration of starlings. He found that the wave from one bird to another moved twice as fast as a human’s visual reaction time and concluded that each bird must anticipate the spreading wave and react before it gets there.
Then the age of computers attracted the interest, not only of biologists and ornithologists but engineers, physicists, and physicians. They hoped to use an understanding of flocking behavior to predict bird strikes on aircraft, to figure out traffic patterns on highways, to comprehend particle swarms and how crystals form, and to gain knowledge about how our brains operate, for example. Some even hoped to use what they learned to understand crowd psychology in humans.
In 1987 software designer Craig Reynolds developed a program called “Boids” of virtual birds based on his observations of blackbird flocks in a nearby California cemetery. He programmed each computer “boid” to follow three rules: avoid collisions, fly at the same speed, and move in the same direction. Scientists interested in collective robotics and crowd modeling, for instance, have cited his work.
But movie buffs should know that the computer-generated swarms of bats and armies of penguins marching and flying in The Batman Returns, as well as battle scenes in The Lord of the Rings and Hobbit films used a software program similar to “Boids.” And Reynolds, in 1998, received an Academy Award for his “Boid’s” design and its importance to film animation.
Beginning in this century numerous studies have continued the search for the how and why of murmuration using computer simulations and citizen science.
First there was STARFLAG—Starlings in Flight—which was a study by European physicists, economists, and biologists from 2004-2007. Using cameras that took photos of 3000 starlings swarming over Rome’s Termini railroad station from two different angles, they discovered that the spatial relationship of flocking birds is based on the position of six or seven nearby birds and that this so-called topological interaction remains the same no matter how large or close the birds are to one another. This allows them to “change shape, fluctuate and even split, yet maintain the same degree of cohesion [because] information moves across the flock very quickly, and with nearly no degradation,” the 12 authors of the study concluded.
Thus starlings can respond to what others are sensing from one side of the flock to another almost simultaneously and evade predators.
Although that seems to answer both the how and why of starling murmuration, observers say that starlings often murmurate shortly before sunset when choosing a place to rest for the night and that there are no predators around.
Andrew Chapman, writing from a semi-urban area near Washington, D.C., watches murmurations at two sites above high rise and mid-rise buildings that coincide with sunrise and sunset like clockwork, yet he’s never seen a predator. He hypothesizes that their murmurations could be predator-evasion practice.
A citizen science study of starling murmuration, conducted by four United Kingdom researchers, collated information from 3000 volunteers in 23 countries, including 70 from the United States. Their two-year study, each year running from October to March when starling murmuration is most common, gathered material on murmuration size and its duration in relation to the location, season, time of day, habitat, temperature and predator presence and behavior.
The size of these flocks ranged as high as 750,000 birds but averaged 30,082 birds. The length of the murmuration was 26 minutes in the U.K., 18 minutes in other native starling countries, and 16 minutes in the U.S. and Canada, and was positively affected by day length and temperature.
Birds of prey were recorded at 29.6% of murmurations and the most common predators in Europe were sparrowhawks followed by buzzards, marsh harriers, hen harriers, and peregrine falcons. But in North America mostly peregrine falcons went after them, followed by red-tailed hawks, Cooper’s hawks, and, in the West, prairie falcons, according to Nick Dunlop, who has been photographing and studying murmuration in California’s Central Valley during migration for years.
The citizen science study found that when a predator appeared, the birds went down together in a murmuration to roost rather than dispersing from the site as they did if there was no predator and thus concluded that starling murmurations were primarily an anti-predator adaptation. On the other hand, they noted that “the murmuration-predator relationship could…be as much (potentially more) driven by murmurations attracting predators—larger murmurations being more attractive—than by predators causing starlings to murmurate.”
So, despite all these studies, the question of why remains an enigma.
But European starling numbers have been falling across northern Europe and the U.K. since the 1980s even though they are thriving in North America. Thus far, ornithologists have not figured out why but have put them on the red list of concern in Europe.
Perhaps, our continent will become the last bastion of safety for these highly intelligent birds. Some researchers speculate about a “group mind” that regulates how flocks survive, especially during migration and fear that once numbers reach a certain low point, such as our passenger pigeons did, they are doomed to extinction.
In the meantime, I will revel in the opportunity to view these unique gatherings of starlings every autumn as they visit for a short time on our mountain, imagining how much more impressive those extinct passenger pigeon flights must have been.