The remarkable life of our swifts
Nature Notes | Bob Jarman discusses the extraordinary lives of these amazing birds.
By now many of our common swifts will have left. In most years there is a main departure at the end of July and the rest leave in early to mid-August for their wintering areas in central Africa, from Angola to Mozambique.
In July and August flocks of ‘screamers’, adults and young birds, can be heard and seen over the city. A September swift is uncommon, while an October swift could even be a rare vagrant, a pallid swift, from southern Europe.
After breeding, swifts will spend the rest of the year eating, sleeping, and migrating, entirely on the wing. This is a round trip – an autumn outwards and spring return of about 12,000 miles! Research using micro-data loggers attached to the birds has shown that individuals are able to live in the air for up to 10 consecutive months, without landing.
Our local swifts arrive between the 5 and 10 May and mate, build nests from feathers and windblown grass stems, hatch and rear their young in just 12 weeks.
Our populations of common swifts are in decline. This might be due to a decrease in flying insects on which they feed but also loss of nest sites because of loft insulation, re-roofing, PVC soffits and, most recently, external wall insulation. Their sleep consists of short periods stitched together as they glide at high altitude.
Compared with other birds, swifts have a high survival rate, perhaps because predators (other than the occasional hobby or peregrine) cannot easily surprise them in the air.
Clarke Brunt has 11 swift nest boxes on his house in Milton High Street.
“Some years they are all occupied,” he said, “but not this year. Most pairs will raise two or three chicks. The best year was 2022 when they raised a total of 31. From laying their eggs it takes 19 days to hatch and the young take 42 days to fledge, so 61 days on average.”
“Most years unpaired single birds attempt to take over an established nest and a violent fight takes place,” said Clarke. “I suspect they are birds in their third or fourth year and are looking for a nesting opportunity or a future nest site when they return next year. This year a local sparrowhawk has learnt how to catch swifts entering their nest box; it wouldn’t stand a chance catching them in flight!”
Dick Newell, a local birdwatcher, is a passionate advocate of our common swifts and an inspiration behind the organisation Action for Swifts. He has been actively installing swift nest boxes in local churches, houses, and schools.
Out of 95 such boxes in Edgecombe flats, there are now more than 50 pairs of nesting swifts. Other new colonies include the east tower of the David Attenborough Building, 40 in Gunhild Way (20 of which are now occupied) and Clare College’s St Regis House in Chesterton Road.
Dick has also led one of the most remarkable observations in field ornithology that I know of. Our common swift is separated into two sub-species: Apus apus apus which breeds in Europe to eastern Russia and winters in central Africa from Angola to Mozambique, and Apus apus pekinensis which nests in central Asia as far as eastern China and winters in south-western Africa. The subspecies pekinensis can be told from apus by its paler brown colour and whiter forehead and chin!
On a visit to Cape Town, Dick noticed that the birds feeding around Table Mountain in Cape Town looked like pekinensis that he had seen nesting in the Summer Palace in Beijing. A chance meeting with Terry Townshend and his contacts with Chinese ornithologists reached an agreement to fit 31 geo-locators to swifts at their nests in Beijing. The geo-locators recorded the positions of the Beijing birds throughout their migrations.
The following year, 13 birds were retrapped, allowing recovery of the data. By analysing the precise times of dawn and dusk, locations could be calculated, and the swifts’ migration routes and wintering areas identified and mapped.
Dick was right. The Cape Town birds were the same as those nesting in Beijing, a round trip of 16,000 miles! Their route was mostly overland so they could feed. On leaving Beijing after breeding, they flew north-west over Mongolia then south-west over Iran and Arabia, and then south into east Africa, through central Africa and down to South Africa and Table Mountain.
What an extraordinary journey, and a remarkable observation!
