During the winter months, if you stay long enough in one of Rome's piazzas (Piazza dei Cinquecento near Termini station is a good one), you'll soon see flocks of starlings taking off from the trees. They fly in elegant, fluid formations that are rather beautiful to watch, but they're the source of a great deal of stress.
It's not so much the birds themselves that are to blame, as their guano. While a single starling's droppings might not amount to much, take them in their hundreds and you've got a blanket covering of stinking, acidic slime that damages monuments and car paintwork, and creates a slippery road surface that causes accidents.
The flocks are a menace in other ways, too: In 2008, a flock of starlings made their way to Ciampino airport, where they were promptly sucked into the engine of a Ryanair Boeing 737. Fortunately, nobody was hurt, but the airport was closed down for two days as a result.
The authorities in Rome are taking a humane approach to the winged menace, and have given Lipu (the Italian league for the protection of birds) an annual budget of €150,000 to deal with the starlings. Lipu operatives approach errant flocks of starlings with megaphones, through which they play recordings of starling distress calls.
It seems to be working: the birds move on pretty sharpish when they hear the sound, and apparently overall numbers are reducing each winter as well.
So if you're walking through town and you hear a hideous squawking, screaming noise, don't worry: it just means that it's probably going to be safe to park your car under a tree.