An increase in urban housing may be harming the numbers of one of Britain's most beloved birds, the swift, according to new research.

The 2007 RSPB Swift Survey interviewed 3,070 homeowners and found that most swifts were recorded nesting in roof spaces, with almost two-thirds of swifts entering under eaves, and another quarter through roof tiles, while one in eight swifts nested in holes in brickwork.

The RSPB warns that such locations are easily removed during renovation and the organisation is now urging people to help swifts by leaving existing nest holes alone wherever possible and fitting internal nest-boxes in new builds or extensions.

Dr Darren Moorcroft, the RSPB's head of conservation management, said: "Swifts have nested on our buildings for centuries and they depend on us for their future. We fear that the UK swift population may be declining, possibly through a reduction of nesting sites caused by renovation.

"Swifts use traditional nest sites, especially in old buildings. If these are destroyed, it is hard to entice the birds back."

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