Sitting on a Rome roof-terrace one early summer evening during cocktail hour, I overheard an American girl ask: Whats with those birds up there?

She pointed to the hundreds of swirling, darting, spiralling, lunging birds in the sky. They seemed to be going nowhere in their never-ending mad carousel, emitting high-pitched supersonic screams as they whirled.

Theyre swallows, eating all those insects that bite you, her companion replied.

He was right about the insects being consumed, but not about the birds. They are not swallows but swifts. Above our heads, above Italian cities, towns and villages, in the summer sky a continual harvest of flying insects is taking place. From dawn until well after sunset, the insectivorous swifts are feeding in the air and cleaning up quantities of nasty mosquitoes, gnats, flies and wasps.

Among the fastest-flying birds in the world, these extraordinary creatures never sit on a limb or a telephone line, never land on the ground to run after or peck at an insect. Almost their entire life is spent in flight; they drink, bathe, collect food and nesting materials without landing. They even mate while flying.

A swift flies at such speed that its not even noticeable when it swoops onto a rooftop or scrabbles under a tile where its made its nest. Its to this nest that it returns at the end of March or the beginning of April after an incredible flight of thousands of kilometres from southern Africa. Under the tiles eggs are laid and the young are raised.

Swifts (rondoni) are often mistaken for swallows (rondini). But swifts and swallows arent related. Even though swallows also feed on flying insects and dart and dash in the air they are not city birds. They prefer the country and construct their nests inside barns, caverns, garages and all sorts of uninhabited buildings outside towns. Unlike swifts, they dont fly in groups and have different flying patterns and wing shape.

Also mistakenly called swallows are their relatives: the smaller house martins (balestrucci) which, like swifts, are city and village birds but build their nests on house walls directly under the eaves.

Swallows and house martins have very different bodies from swifts. The swift is all wing, a short torpedo-shaped body and a short tail. They are also entirely black, while swallows are a shiny dark blue with a white belly and distinguished by a long, forked tail.

Swallows and house martins can land on the ground and sit on telephone lines. If by accident swifts find themselves on the ground or on a flat surface, they have great difficulty taking off again, hindered from rising quickly and steeply by their long narrow wings. They always nest and roost with a drop below so they can then launch themselves out into the air the drop giving them the necessary speed and lift to continue.

Swifts have been known to bump into one another while swirling through the air or hit a wall or a window, fall to the ground and then not be able to take off again. If a kind person sees this helpless bird sprawled, wings spread, it should be picked up, held in the open palm of the hand and given a quick upward lift. If it isnt injured in any way, it will zoom off, saved by this small gesture.

Often a baby swift can be found on the pavement having crawled out (or been kicked out) from under its tile and fallen off the roof. It cant be returned to the nest and cant be left to die. Its not so difficult to save it. The only requisite is a bit of tender loving care. You can help in one of two ways:

If in Rome, call LIPU (Lega Italiana Protezione Uccelli) centre for bird rehabilitation (saving and returning fauna to their habitat). LIPU has volunteers and professionals working round the clock who will take the bird in any condition.

Alternatively, wherever you are, you can patiently raise the bird yourself for two or three weeks. You will need a shoebox with air holes and paper towels for changing under the bird. The bird needs to be fed hourly with a few bits of ground raw beef or cat food, or even dead flies and other insects, as well as the occasional drop of water. The important thing about the feeding is to insert the food deep down in the swifts throat. Tweezers work well for ground beef or dead insects, or a syringe (without needle!) for mashed cat food. When the baby swift opens its wide mouth tweezer or syringe can be popped in. The bird stays in the box until ready to fly, as though it were under a roof tile. It can be taken along in its box on whatever errands have to be done during the day, with just its small nourishment in a jar for the hourly feed. It will even spend the day in an office without any trouble.

When the wings are fully feathered the fledgling should be held in the palm of the hand and tipped up and down to help it flap and get the feel of its wings in preparation for its release back into its environment.

How do we know when our bird is ready to take off? When the wings, folded, are two centimetres longer than the tail.

At dusk, when the swifts are concentrated in the sky, our fledgling can be taken outside and given a boost from an open palm. Up it will streak into the sky, disappearing among its companions.

We are not grateful enough to these marvellous swifts for the pesticide-free clean-up of so many of the flying nasties. We only notice the difference after the swifts have departed, in mid-July, to take up that mysterious arduous trip back to Africa, when their task of nesting and chick-raising is over. Then the flying creepy crawlies descend on us in full force, with nothing but bug spray to protect us for the rest of the summer.

LIPU Centre, 1 Viale Giardino Zoologico,

tel. 063201912. Daily 09.30-17.30.