They were far more loyal to a nest than to a mate
Each spring, a small bird crosses continents to return not merely to a country or a coastline, but to a single crack in a single wall — and finds, with increasing frequency, that the wall has been made whole against it. A fifteen-year study of swifts nesting on Dartmoor has given scientific weight to what naturalists long suspected: these birds are more faithful to their nest sites than to their mates, returning to the same spot 94 percent of the time. Against this portrait of extraordinary loyalty, Britain's 70 percent population collapse since 1995 reads not as ecological abstraction but as a quiet erasure of individual lives and ancient attachments — one sealed roofline at a time.
- Swifts returning to a Dorking breeding site this season found the entire building demolished, a scene repeating itself across Britain as renovations erase nesting cavities that birds have used for generations.
- A fifteen-year RSPB study of 190 birds has now quantified the stakes: swifts abandon partners before they abandon nest sites, making each lost cavity a potentially permanent severance from the species' future.
- Scotland has mandated swift bricks in new construction, but England's government continues to refuse the same £35 requirement, leaving campaigners like Hannah Bourne-Taylor watching hard-won momentum reverse south of the border.
- A heatwave is bearing down on current breeding season, threatening to overheat chicks in their nests and adding acute pressure to a population already in structural decline.
- Grassroots resistance is accelerating — over 150 local swift groups now operate across Britain, Network Rail reopened blocked viaduct holes after public outcry, and community volunteers are mobilising to rescue fallen swiftlets as UK Swift Awareness Week begins.
A swift is more faithful to its nest than to its mate. That is the finding at the heart of a fifteen-year RSPB study tracking 190 individual birds across 243 nests in a Dartmoor village: 94 percent returned to the exact same site each spring, while only 59 percent stayed with the same partner. Territorial disputes caught on nest cameras revealed just how fiercely these attachments are defended. The data, published as UK Swift Awareness Week begins, transforms a long-held suspicion into documented fact — and makes the species' ongoing collapse all the more legible as a tragedy.
Since 1995, Britain's swift population has fallen by 70 percent. The cause is not mysterious: when old buildings are reroofed, insulated, or renovated, the small gaps where swifts breed are sealed away. This spring, birds arriving at a long-established site in Dorking, Surrey, found the building itself gone. The pattern is national in scale and accelerating.
The remedy is inexpensive and proven. A hollow swift brick — roughly the size of a standard building block, costing £35 — can replace what renovation removes. Scotland made such bricks mandatory in all new construction this year. England has repeatedly declined to follow, despite years of campaigning by naturalist Hannah Bourne-Taylor, and despite the Labour government reversing earlier support for the measure.
Still, the response from below is growing. More than 150 local swift groups now operate across Britain, from Aberdeen to Devon. Network Rail, after public pressure, reopened blocked holes in a Derbyshire viaduct. Volunteers stand ready to rescue swiftlets falling from overheated nests during the current heatwave — a risk that grows each summer. "Every year more people get involved and take action," said Swift Awareness Week coordinator Nick Brown. The government has declined to act, but the birds, it seems, have found other advocates.
A swift returns to the same nest site year after year with a fidelity that puts human relationships to shame. Scientists tracking 190 individual birds across 243 nests in a Dartmoor village over fifteen years found that 94 percent came back to the exact same spot each spring. They were far more likely to abandon a mate—only 59 percent stayed with the same partner—than to leave their nest. The birds' fierce attachment to these sites, sometimes erupting into visible territorial disputes caught on nest cameras, reveals something essential about their survival: they need those specific places to live.
The problem is that those places are disappearing. Since 1995, Britain's swift population has collapsed by 70 percent, a decline driven almost entirely by the loss of nesting cavities in buildings. When old houses get new roofs, when walls are insulated, when structures are renovated for modern living, the small gaps and crevices where swifts breed vanish. The birds return in spring to find their ancestral homes sealed shut or demolished entirely. This year, swifts arriving at their breeding site in Dorking, Surrey, discovered contractors had torn down the building where they had nested for generations.
The solution exists and costs little: a hollow brick, roughly the size of a standard building block, designed to provide a nesting cavity. Scotland made these swift bricks mandatory in all new construction this year. England's government has repeatedly refused to do the same, despite the brick costing only £35 per home. The naturalist Hannah Bourne-Taylor has spent four years campaigning for this single requirement, winning in Scotland but watching the Labour government reverse its earlier support for the measure south of the border.
Malcolm Burgess, principal conservation scientist at the RSPB, which conducted the fifteen-year study, emphasized what the data now proves: "We've anecdotally thought for a long time that swifts are loyal, returning to the same nesting sites and partners each spring. But for the first time, we've documented just how strongly faithful they are to their nest sites, which highlights just how important it is to protect their nesting sites in our neighbourhoods." The research, published as UK Swift Awareness Week begins, provides the clearest evidence yet that protecting existing nests and creating new ones is not optional—it is the difference between the species' survival and further decline.
Yet there are signs of hope, though they come from unexpected places. When Network Rail discovered that holes in a railway viaduct in Derbyshire had been blocked, a local outcry prompted the company to reopen them for the swifts. More significantly, the grassroots response to the birds' plight is accelerating. More than 150 local swift groups now operate across Britain, from Aberdeen to Devon, running events and rescue operations. Nick Brown, coordinator of Swift Awareness Week, noted that community enthusiasm for the birds is "growing exponentially." Volunteers stand ready to rescue swiftlets that fall to the ground—a growing risk this year as an intense heatwave threatens to overheat chicks in their nests. "Every year more people get involved and take action," Brown said. The government may have declined to mandate swift bricks, but ordinary people, it seems, are taking the matter into their own hands.
Notable Quotes
We've documented just how strongly faithful they are to their nest sites, which highlights just how important it is to protect their nesting sites in our neighbourhoods.— Malcolm Burgess, RSPB principal conservation scientist
The interest and enthusiasm and care for swifts is growing exponentially. Every year more people get involved and take action.— Nick Brown, Swift Awareness Week coordinator
The Hearth Conversation Another angle on the story
Why does a bird's loyalty to a nest site matter so much? Couldn't they just find a new one?
Because swifts spend most of their lives in the air—they eat, sleep, and mate on the wing. A nest site is their only anchor to survival. If it's gone when they return from Africa, they have nowhere to breed. They can't just build a new one; they need a cavity in a building.
So the 94 percent figure—that's saying almost all of them come back to the same spot?
Yes. And it's higher than the rate they stay with the same partner. That tells you how critical the physical location is to their biology. It's not about preference; it's about necessity.
If Scotland made swift bricks mandatory, why hasn't England done the same?
The government has refused repeatedly. It's a £35 cost per home, which developers argue adds up. But the alternative is watching a species that's already declined 70 percent disappear entirely from our towns and cities.
What happens to a swift that comes back and finds its nest demolished?
It can't breed that year. It may try to find another site, but swifts are so specialized that most don't succeed. Over time, if enough nests are lost, populations collapse—which is exactly what we're seeing.
You mentioned community groups are growing. Are they actually making a difference?
They're creating new nests where government won't mandate them, rescuing birds in distress, and building public awareness. It's not a substitute for policy, but it's keeping the species alive in places where it would otherwise vanish.