Swift

The swift (Apus apus) is remarkable for spending almost the whole of its life airborne, only “landing” to build a nest and raise a brood. During its lifetime of ten or more years a swift may fly well over a million miles.

Apperance

Swifts are often mistaken for swallows, although they are not closely related. The swift is 16-17 centimetres (6-7 inches) in length, which is shorter than the swallow, but the wing span is much greater (up to 44 centimetres for the swift as against the swallow’s maximum of 34 centimetres). However, the scythe-like shape of the swift’s wings is unmistakable. The tail-fork of the swift is also less pronounced than that of the swallow.

The swift’s plumage is sooty-brown above and below, on body, tail and wings, with a lighter patch on the throat. When seen from below the swift appears black against the sky.

The swift has evolved for life aloft, to the extent that its legs are so short that, should it land on the ground, it may find it impossible to take off again. The only purpose of its feet is to grip the edge of a vertical surface when nesting.

Behaviour and feeding

Swifts breed in the northern hemisphere and winter in southern Africa. A British-born swift may spend only about a third of its life in Great Britain, given that swifts arrive in late April or early May and leave again in August.

On fledging, a young swift immediately heads south, without its parents, and is likely to stay on the wing until it is ready to breed, three or more years later. It will eat, drink and even sleep while in flight.

Swifts feed continuously on a wide variety of flying insects and airborne spiders, and may consume as many as 10,000 in a day. They will cover large distances in their search for food, and have been known to fly for 100 miles to avoid bad weather.

Birds can fly to considerable heights, alternating rapid wingbeats with glides. Groups of swifts can sometimes be seen spiralling out of sight in the evening so that they can sleep as they glide back down.

Swifts can live up their name by flying at speeds of up to 70 miles an hour.  Their migration flights are rapid, with swifts only taking two or three weeks to fly from Europe to southern Africa.

Swifts are noted for the high-pitched screams they emit, especially when chasing each other round rooftops on fine evenings.

Breeding

When swifts eventually breed a nest will be built from material such as straw that is gathered on the wing and stuck to a vertical surface, such as the wall of a barn, with saliva. Once a nest is built, a pair of swifts, who bond for life, will use the same site year after year.

A clutch of two or three eggs is laid, with the young hatching at staggered intervals.

Breeding begins in May, when a period of colder weather may intervene. Should this happen, the normal incubation period of 19 days may be extended. The parent birds are also able to go into a state of torpor, hanging on the wall until the weather improves and the swifts’ food supply of flying insects becomes available again.

One problem for swifts is that modern buildings do not offer the same nesting opportunities that traditional ones do. Swifts are also disadvantaged when the owners of buildings block holes to prevent pigeons from nesting. Bird lovers can help swifts by providing nest boxes in suitable locations.

© John Welford