The joy of summer to some is signalled by the return of the Common Swift. In groups, swirling above our heads, their calls known as ‘screaming parties’ can often be heard from late spring. High over the rooftops, these masters of the sky can remain unnoticeable, unless you witness their majestic acrobatics and top speeds of up to 69 mph. For enthusiasts, once seen, never unseen. With their curved wings and forked tail, these brown birds are summer visitors to the UK.
The Common Swift (Apus apus), however, is now not so common in the UK. Numbers are plummeting and they have been placed on the UK’s Red List of Birds of Conservation Concern. It is reported that for every ten swifts flying across our skies in 1995, there were only about three by 2022, and numbers continue to fall.*
The Master at Darwin College at the University of Cambridge, Dr Mike Rands, spoke about these magnificent and enigmatic birds as they nest at the David Attenborough Building and other buildings around the University, and what is being done to help encourage their return to Cambridge.
Common Swifts nesting at the University of Cambridge in the Old Schools Buildings in the city centre
The Master of Darwin talks about the habits of the Common Swift
“May is my favourite time of year, early May, especially because that’s when swifts arrive here in the UK, and you can see them swirling above Darwin College, and many other parts of the University and in the wider Cambridge area,” he said. “Swifts are amazing birds. They spend almost all their life on the wing, sleeping, eating and even mating, and only landing when they come to nest, here, in nest boxes usually.”
Dr Mike Rands, also the Founding Director of the University of Cambridge’s Cambridge Conservation Initiative at the David Attenborough Building, and former Chief Executive of BirdLife International, explained more about the life and behaviours of this small brown migratory bird.
“In the winter, they are flying around in Africa, south of the Sahara, feeding on insects, and astoundingly, on their migration they travel 14,000 miles between here and Africa, moving at very high speeds. They can cover roughly 600 miles in one day. Absolutely amazing birds.”
Dr Rands spoke on the swift’s eating and drinking habits, some of which are hard to study due to the birds being airborne most of the time: “The Common Swift feeds on aerial insects, mainly flying insects, but remarkably quite a lot of those spiders that you see on threads in the air are also part of their diet. And they need and eat up to 20,000 insects a day. Extraordinary, that’s how they survive.”
He explained that swifts are most likely to be seen in the mornings and early evenings if it is a hot day, “as with the heat, the swifts will rise higher in the sky to feed, as do the insects. So your best chance to see them is when the temperatures come down or when they are swooping into their nests.” He said that when they drink, “they simply come dipping down to ponds or lakes or rivers and scoop up the water. So, they do not land at all, except to breed.”
The Common Swift is a bird about which less is known perhaps than other garden birds, but an interesting fact for swift enthusiasts, Dr Rands explained, is that: “The birds also have a flightless parasite, the swift lousefly (Crataerina pallida) which look quite ugly. You will see them in the nests. They appear to have evolved their flat shape so that they may cling on to Swifts when the birds fly at speed.”
Swifts also mate on the wing and only use the nest to lay eggs and rear their chicks. And once the chicks are fledged, Dr Rands explained, “they spend up to three years on the wing before they actually return to a nest site, which is usually very close to where they were born.”
Common Swift on the wing
The Master of Darwin talks about the nesting challenges for the Common Swift
Dr Rands said swifts urgently need our help: “Unfortunately, swift populations in the UK, and indeed, around the world, have declined significantly. We think it’s about a 70% decline since 2015. That’s really steep.” He said the main reason for that “is probably a lack of nest sites, but also insect numbers have declined enormously, and that may have affected them, and I’m afraid climate change may be having an impact.”
Historically, swifts used to nest in buildings, and even in cliffs and caves. “But now nest sites are at a real shortage,” Dr Rands explained, adding, “In order to address that problem across the UK, people are now putting in artificial nest sites. In some parts of the country, including in Scotland, it’s actually now a legal requirement that when a new building is created, a swift box or a swift brick is put into the building. So that’s providing artificial nest sites, but they work very well.”
“One of the things that the University of Cambridge is doing to try to help recover the swift population is to put nest boxes on buildings around the University to compensate for the fact that natural nest sites have disappeared as a result of new modern buildings,” Dr Rands said.
Common Swift nest boxes on the buildings at Darwin College, University of Cambridge
Common Swift nest boxes at the David Attenborough Building
Dr Rands pointed to the work at the David Attenborough Building by way of example. While Executive Director of the Cambridge Conservation Initiative, Dr Rands was responsible, along with a group of colleagues and the help of Dick Newell from Action for Swifts, for putting up the first swift boxes on the outside of the building’s tower in 2020. The boxes had to have special tunnelled designs that extend out from the tower to give swifts access. To attract swifts initially, swift calls were played over speakers which could be heard as far as Pembroke Street below. The method worked.
Dr Mike Rands, standing beside the first nest boxes put up in 2020 at the David Attenborough Building, University of Cambridge
The scheme at the David Attenborough Building, which just celebrated its tenth anniversary, and which has swift motifs on many of its internal doors, has since expanded to 20 Swift nest boxes, with 24 nesting chambers. The first pair nested successfully in 2021, rearing two chicks. Each year, more pairs take up residence. Some have live cameras on the nest. Dr Rands said, “You can actually watch the birds laying their eggs, their chicks hatching and being fed by the adults, and even their lousefly parasites.”
Common Swift nest boxes high up on the David Attenborough Building tower at the University of Cambridge
Common Swift nest boxes and the natural and historic nesting sites around the University and Colleges
Swift colonies can be found elsewhere at the University. At the North-West Cambridge development at Eddington, for example, the biodiversity team has installed more than 200 bird boxes on site and a number of those are for swifts. Each year swift call sounds are playing on site to encourage them to use more of the boxes. This year, swifts have been seen using boxes, with swifts regularly being seen feeding over the site each summer.
Swifts are also this year at the Old Schools, Trinity Lane, where they were spotted nesting in the building bricks above Cobble Court. A number of Cambridge Colleges also have their own colonies and action plans to encourage the swifts to nest.
Dr Rands talks about his own College, Darwin, and action they are taking to provide nest sites. “It is fantastic to see them back here now, above Darwin College. I’m particularly pleased this year, because three years ago we put some nest boxes up and we are playing tapes of the calls, which we know attracts the birds in, but it usually takes a year or two for them to establish a colony. And I think, touch wood, we have actually got birds nesting in one of our nest boxes for the first time this year. So we will watch this space with great excitement.”
Common Swift in flight high in a blue sky
Dr Rands spoke about what swifts mean to him. “Personally, I really love swifts. I think they’re such remarkable birds. And in the evenings, you can hear them swirling round, especially soon after the young have hatched, screaming it’s called. I don’t think screaming is quite the right language for it. I think it’s a much more attractive sound than that. I think they’re very special and a remarkable reminder of how wonderful the natural world is and how important it is for our own well-being.”
