Swifts, the quintessential birds of high summer, are declining so rapidly in Britain that they are to be the subject of a major census.
The Royal Society for the Protection of Birds (RSPB) is launching a nationwide search to identify where swifts are still seen and could be nesting. The key cause of their dramatic drop in numbers is thought to be the loss of nest sites in buildings, through property improvement or demolition.
Swifts have declined by 47 per cent since 1994, and this year the dark, scimitar-winged migrants have been added for the first time to the Amber List of Birds of Conservation Concern, meaning the threat to their future is considered serious.
Swifts come to breed in Britain every spring and stay for the shortest period of any migrant, arriving in May and leaving as early as mid-July. Their distinctive arrowhead silhouette is seen by many as a symbol of summer.
Like members of the swallow family – which they resemble in appearance, but to which they are unrelated – they have adapted to human habitation, squeezing through gaps under the eaves of houses, town halls and churches to make nests, typically on the beam on which roof rafters rest, where they are safe from predators.
But the way is being barred. Many buildings erected in the past 50 years do not have such gaps and, as older housing is renovated, nesting opportunities for swifts are disappearing all over the country. Modern buildings, especially those made using steel and glass, are a swift no-go area, and numbers are tumbling.
Now, the RSPB is seeking to build up a detailed picture of exactly where the birds are nesting, so the sites can be safeguarded. The charity is asking people to look out for the birds entering a roof or hole in a building, or to record swift "screaming parties" – groups of the birds which speed through the air on warm summer evenings letting out loud shrieks.
Once the society has discovered more about where swifts are found it will focus its conservation efforts on areas where they are commonly seen, and work with the building industry to help birds in buildings.
Swifts spend their lives almost entirely on the wing and feed, drink, sleep and even mate in flight.
"Sharing your house with swifts is a great privilege," said RSPB species recovery officer Sarah Niemann.
"They are not obtrusive at all, in fact they make perfect neighbours. They build their nests right next to the entrance hole so they don't get into your roof space and they cause no damage," she said.