The Sky-High Mob Over Rome

ROME, Nov. 17, 2008 -- The autumn skies of Rome at dusk belong to the starlings.

Lifting off from their plane-tree roosts along the Tiber river, they slowly gather. A small flock flies about and is joined by another small flock. Yet another joins them, and then another and they become a sky-high mob.

Seen from a roof terrace in central Rome, they resemble circus acrobats warming up for their finale with somersaults and arching pirouettes. They are their own amusement park ride, dipping and soaring with switchbacks and loop de loops.

Hundreds and then gusts of thousands glide over the domes and antennaed rooftops. Sometimes, when the birds fly low enough, you can hear the whoosh and a faint murmuring as they pass overhead. They seem to be heading for a certain somewhere until they veer off in another direction entirely.

Claudio Carere is an ornithologist who has been watching the starlings in Rome since he was a boy.

"These gorgeous aerial displays, which include merging, splitting and turning, are all part of the collective anti-predator response," Carere, 41, said, "and they are effective in reducing predator success."

Starlings are not new to Roman skies. Pliny the Elder, a first-century writer, noted that by observing that starlings in flight, one could predict the future. He also noted that Nero, the notorious Roman emperor, kept one as a pet.

Since the early 1920s, starlings have been arriving to winter in Rome in large numbers, with current estimates at 500,000. They arrive in mid-October -- attracted by the city's warmth, safety and green areas -- and depart in mid-March, flying off to breed in Central and Eastern Europe.

Although the birds put on an entertaining display, not all the wingless inhabitants of Rome are applauding. The problem: excrement.

Under the trees where the birds roost, the pavement and cars are covered in the stuff and the city of Rome has decided to take action. With assistance from bird-protection enthusiasts, starlings' distress calls are recorded, amplified and then played back through loudspeakers in the hardest hit areas of the city. The idea is to scare them away but this only works if it is repeated consistently; otherwise, they come back in two or three days.

Carere isn't bothered.

"Italians love their cars and they don't like them to be covered by bird droppings," he said. "They only have to avoid parking under trees where the birds roost -- just like you wouldn't park where your car might be robbed."

Flight of Starlings

Working for the EU-sponsored Starflag project -- the first large-scale study of collective animal behavior -- the scientists studied the starlings' flocking behavior and analyzed it for its similarities with social-human behavior.

A team of researchers from the National Physics Institute of Matter in Rome, who participated in the project, invented a 3-D method of determining the birds' trajectory by matching their positions in photos taken at regular intervals.

This led the researchers to establish that every starling keeps about six or seven birds in its scope as reference and transfers information among the group, producing the flight patterns we see. The starlings are not exactly counting their flying companions to keep track of them but instead using pre-numeric capabilities.

"After three years of research, we, too, are very attached to these birds," said Irene Giardina, one of the researchers in Rome. "We, as physicists, couldn't fail to be amazed by the phenomenon -- all those evolutions in the sky. It led us to think of similarities in our field and we applied that knowledge to study their behavior."

What has also been discovered is that the starlings can fly in very close formations -- less than a foot between them -- and produce high-density wave formations in the sky in response to predators.

"These 'waves,' which are moving incredibly fast, are highly successful in reducing predator attack. Each flock of thousands of starlings can generate up to 20 waves in 15 seconds," said Carere, who has been working alongside the Starflagresearch team for the last two years.

"Their song is amazing too. ... They seem to chat," he said. "Their vocal repertoire is vast and they can imitate sounds ... traffic sounds, even the sound of an ambulance."

In the dying light of an autumn evening in Rome, they are still magic and mystery. The starlings swarm and buzz above the heads of the statues in Roman parks, and pass over and around St. Peter's dome as if seeking a blessing from the pope.