Our new research shows that 9 out of 10 Swifts reuse the same nesting site.
3 min read
The latest RSPB research reveals the true loyalty of the Swift – the fastest bird in level flight. Our 15-year study shows that when looking at places to breed, most Swifts try to return to the same nesting site each spring. Nine out of ten (94%) birds used the same nesting site as a previous year.
Over 15 years, our researchers collected data from Swifts breeding in nest boxes in and around a Dartmoor village. Breeding Swifts were fitted with uniquely numbered leg rings. These enabled scientists to track which birds bred together and which nest box each Swift nested in every year. We collected data from 243 nests during this period.
Where the team were able to identify both birds from a pair for two years in a row, they found only 5.5% (3/55) known to have returned had “divorced” and found a new partner. Over the course of the study, 59% of pairings were between previous partners. Across the 15-year period, the majority (95%) of Swifts returned to the same nesting site to breed. For Swift pairs which stayed together for two or more years, 89% reused the same nest site.
Historically, Swifts have made use of small crevices and holes in buildings to raise their chicks. But new building methods have left them increasingly few spaces for nesting. However, the species has declined by 70% (1995-2024) in the UK likely due to loss of nest sites and availability of insects.
This research shows just how important it is to maintain existing Swift nest sites. Increasingly, many Swifts return from their long migration to find their traditional nest site blocked up or gone entirely. This forces the birds to expend extra energy and time searching for an alternative. Nest sites can be hard for Swifts to find due to fewer spaces being available in modern and renovated buildings. Providing specially designed nest boxes or Swift bricks is becoming increasingly important, but the fitting of Swift boxes to new buildings is still not compulsory and is only encouraged by planning policy rather than required by law.
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 decline in Swift numbers is a great cause for concern and without increasing the availability of nest sites, and replacing those that are being lost, we will see further declines of this extraordinary bird in our towns and cities.”
The strong bond between Swifts and their nest site shows just how important it is to ensure they have a place to return to each year.
This year, Scotland became the first UK country to make installation of Swift bricks, bricks designed to provide an ideal space for Swifts to nest in, a legal requirement for new buildings. This will help safeguard the future of this threatened species. Despite much campaigning, the rest of the UK still falls short of this simple measure. It is clear from this new research that if Swifts continue to lose the nest sites they return to each year and not enough suitable new nest sites are made available, they will eventually be lost from our skies.
