The number of swifts visiting the UK is in decline
A UK-wide survey of nesting swifts has suggested the declining bird species is at risk from improvement work being undertaken on old houses.
The RSPB study of more than 3,400 swift nest sites found nearly 80% were on houses, more than half of which were homes built before 1919.
It is not known why the birds are in decline, but numbers have fallen by almost a third in the past decade.
The charity says building work should not be done while swifts are nesting.
The birds tend to return to the same nesting sites each year and the RSPB said it was concerned the birds were suffering as a result of demolition and improvement works.
More than half the sites located in the survey had been known nesting places for swifts for more than 10 years, and about one in six spots was under threat, the RSPB said.
Emma Teuten, the RSPB's data management officer, said: "These are birds that don't touch down for two years or more after they first leave the nest - we need to make sure they have a safe, secure nest site to settle in when they come down to breed themselves."
Sarah Niemann, RSPB species recovery officer, said: "The scream of the swift marks the start of summer for many people. To think that we are losing them at such a fast rate is devastating.
"It was imperative that we find out exactly where they nest, so that efforts to help them can be effectively targeted."
Swifts make their nests in holes in buildings from where they can launch themselves back onto the wing as they cannot take off from the ground.
Their nests are protected by law while they are in use, so work on homes with nesting swifts should be done before they arrive in mid-May or after they leave in mid-August, the RSPB said.
The charity is appealing to the public for help spotting nests and talking to local councils and developers about how to retain and replace nest sites.