Swifts feed, sleep and mate in the air, only landing at their nesting sites
Sussex's breeding population of swifts is "falling fast" as redevelopment and DIY work deny them nesting sites in old buildings, a bird society has said.
The Sussex Ornithological Society (SOS) said the county's population dropped by more than half between 1994 and 2007.
The SOS is asking people to "spare a thought for swifts" when renovating old buildings or designing new ones.
Swifts fly 7,000 miles from Africa to nest in wall cavities and roof spaces in the UK during the summer months.
A spokesperson for the Sussex Ornithological Society said: "Swifts are a welcome feature of the Sussex summer, and we must do what we can to help to maintain a healthy breeding population."
The society suggested that swift-friendly features could be incorporated into buildings and stressed this was particularly important at or near existing nests.
Possible measures included building swift nesting bricks into walls, putting up 'swift-only' nest boxes, and providing access to roof spaces.
Swifts feed, sleep and mate in the air, only landing at their nesting sites.
Other species also affected by the trend of redevelopment and improvement include house sparrows, swallows and house martins.