The swift population in London is a shadow of its former self, the UK's leading bird and wildlife charity has revealed.

At this time of year the skies of Hounslow are alive with the distinct screams of the swifts overhead after their return from Africa where they escape the cold English winter.

Drought in Africa has made their survival there difficult and when they fly to the UK to breed they often cannot find their old nests. Modern building design does not offer the nooks and crannies that older architecture provides for ideal nest building.

To help correct the lack of cosy nesting spots, the RSPB charity is urging the public, especially businesses, to get swift boxes to attach to sleek new buildings.

The swift's nest is a simple shallow cup made of grass, leaves and feathers, cemented together with saliva. Many modern houses lack nest holes common in older homes but the swift nest boxes or bricks can be a good substitute.

RSPB London spokesman Tim Webb said: "The best thing we can all do for London's wildlife is manage our gardens and open spaces with them in mind."

It is the only bird known to sleep on the wing. Before dusk the birds gather and ascend high up in the air to roost in a warmer air layer some 1,000 to 2,000m above ground. Swifts even mate in the air.

To find out how you can help swifts phone the RSPB on 0207 808 1240.