The Common Swift and Nest Boxes – 2026 update
This is part of a series of notes and observations on Swifts and our attempt to persuade a pair to adopt one of our nest boxes. It is also the context for describing the amazing and complex behaviour of these wonderful birds. The more we learn about them the more fascinating they become.
Although they are sometimes referred to as the European Swift (Apus apus) they spend relatively little time in Europe. They arrive here between the end of April and beginning of June and depart as early as the beginning of August, heading for their wintering grounds across Central Africa.
And when they are here we don’t necessarily see that much of them. They fly high and fast, and when weather conditions are poor they can easily depart to feed up to a 100km away from where they are nesting.
They are at their most prominent when the juveniles arrive in early June, and form noisy groups that scream with excitement as they fly at speed, especially during evening time. These groups of juveniles contain birds from one to four years old. The older juveniles will be on the lookout for mates and a suitable nesting site for the following year.
They nest in small colonies and will be attracted to existing nesting sites with breeding adults – hence the importance of using a swift caller when trying to encourage the first pair to adopt a box.
The Story So Far – 2023 to 2025
Three boxes went up in 2023. A camera went into each in the hope of seeing something of the nesting behaviour of these extraordinary birds. To attract them to the boxes we set up a small directional speaker on an adjacent window sill to project a recording of the territorial / defensive call of the Swift towards the box – see Part 2: Nest Boxes and the Attraction of Swifts:
The result was plenty of Swifts, but all ignored the boxes. One possibility was that the call wasn’t sufficiently directed to a box, and so in 2025 we fitted a camera and small speaker inside a new box and added this to the row of three.
We started the internal caller in mid-April 2025 and continued to use the directional speaker on the windowsill. Although we saw less Swift activity during the summer than in previous years we finally got the result we were after, a number of juvenile Swifts entered the box, including a pair that returned regularly for several days.
The layout of the new box and the behaviour of the Swifts in relation to the internal caller is described and explained (as far as we are able!) in The Common Swift and Nest Boxes – 2025 update:
A cold dry April and early May, and no views of Swifts until the 20th when we began to have regular views of ones and twos flying high and feeding.
On the 20th we saw the start of an exceptionally warm dry spell, with temperatures well into the twenties.
On the 25th we had our first view of a pair of Swifts flying low in the proximity of the boxes. On the same day at 4.00pm two entered the box and stayed until after 4.00am … a 12 hour stint.
For the next five days they maintained this schedule of about 12 hours in the box and 12 hours out, although on the 26th and 29th they also returned during the day for an hour and a half.
Our assumption is that these birds are the pair that explored the box in 2025. They entered the box quickly. There was nothing tentative and exploratory about their behaviour, as we saw from them last year. Also, as yet we haven’t seen or heard the screaming parties of unmated birds that usually arrive in the UK in early June.These come well after the established pairs have returned to claim their nesting sites from the previous year – they are nest-site faithful year on year, and will defend their site against prospecting youngsters.
It is wonderful see their intimately entwined bodies on the nesting pad. Rarely still for more than a few minutes, they are constantly preening themselves and each other. Sleep as we understand is fleeting, but of course this is for birds that sleep on the wing when they are not at the nest. There is still so much to learn and understand about these birds.
see The Intimacy of Nesting Swifts:
DIARY
Because of building work on the house we didn’t switch on callers until the 21st May. But we hadn’t seen much activity before then, certainly not compared with the previous two years. There is one caller on the window sill adjacent to the boxes, and one in one in the boxes.
Arrival
On the 22nd May we saw five Swifts circling low. On the 24th two came close to the box at 11.00am. At 4.00pm two entered the box and stayed until a time between 4.00 and 6.00am in the morning. We assumed these were the same two birds that visited the box last year. They showed no hesitation in entering the box, and settled very quickly.
The following day they arrived at 11.00 stayed for an hour and then returned at 7.45pm and stayed all night. This became the pattern for the next few days. During this time, they brought in a small piece of string and a feather, which was their token nest building behaviour.
The First Egg
On 1st June, seven days after they arrived, they remained in the box later than usual. The male made occasional forays to the entrance and back. The female stayed on the nest pad until 10.30am, when we saw an egg. Neither bird seemed to take any notice of it, and both left at 11.00am. For the next 24 hours the egg remained to the side of the nest pad, and then it disappeared out of camera view.
The Second Egg
On the 4th June both Swifts remained in the box until about 11.00am. When they left a second egg was on the side of the nest pad. This eventually ended up wedged between the pad and the corner of the box. It remained there until the 7th June. On that day both birds left the box early. At 8.00pm one returned. It started nibbling and depositing saliva around the edge of the pad. It then turned, picked up the egg, which fitted easily into its wide gape and disappeared off camera with it. I checked under the box. No egg had been thrown out, and so we assume it is laying at the front of the box with the first.
The Third Egg
Between the 8th and 20th of June, our weather veered from normal to extreme in terms of temperature, at times reaching 38C. During this time the birds were spending much of the day out of the box, leaving between 7.00 and 8.00 in the morning and returning around 8.00 in the evening, with occasional short visits to the box during the day. They had also started to bring in white feathers, sometimes two or three in a day which one of them would stick to the edge of the nest pad.
On the 20th they remained in the box later than usual, and sure enough a third egg was laid. This time the birds’ behaviour was markedly different, or at least the behaviour of the female. For 48 hours we saw her clearly incubating the egg. She stayed in the box for all of this time, and would gently tuck the egg under her. We thought this was the beginning of a proper incubating process. (This was also a day of record-breaking heat.)
The male returned in the evening and spent the night in the box tucked along side her.
On the 23rd however, things changed. At 7.00am we saw one bird in the box sitting tight on the nest. The other bird, presumably the male, was in and out a couple of time. At 1.00pm we saw one of the birds manoeuvring on the pad and inadvertently threatening egg that had been pushed to the edge of the pad. Inevitably it went off the pad and disappeared from view. From its behaviour we assumed it was the male bird that had taken over from the female, but we have no evidence for this. From 2.30 to 5.30 one bird sat on the nest as though there was an egg. It then left the box. Both returned around 9.00pm and stayed the night.
Nest Building
Up to this point, the nest was extremely rudimentary. The feathers that had been brought were tucked along the back edge of the pad, between the pad and the wall of the box. It was only after the loss of the third egg that they began to take feather collection seriously.
Feathers were now being brought in and stuck round the edge of the pad, and were overlapping into the centre of the pad. By the end of June the pad was beginning to look like a nest that could contain eggs.
By its very nature, the construction of a Swift nest is a time-consuming affair. We have watched many different bird species building nests. Most find a source of material and go back and forth constructing deep or intricate nests, some so intricate that it is amazing how such complex behaviour can be inherited through their genes.
The Swifts however have to find their material as it floats in the air, there is no source for them to aim for. Their skills seem very basic, essentially saliva glue and a feather. But there is no doubt that this instinctual behaviour needs to be triggered.
Our two Swifts are young birds. They arrived, and their instinctual breeding behaviour was not synchronised. Two weeks of bonding, then the eggs, which were lost, and now the intensive nest building behaviour. They will continue this until they depart sometime from mid-July. Hopefully both will survive the journey to and from Central Africa. If so, they are almost certain to return to this nest site. They will find the nest, repair it as necessary, lay eggs and rear young!
Diary to be continued …..
NOTES
1. Egg Laying and Incubation:
- Swifts sometimes abandon the first clutch of eggs;
- They tend to lay between 8.00 and 11.00 am;
- They can leave eggs unattended for long periods, up to several days, without affecting the development of chick, or even delaying it.
2. Screaming Parties:
The highlight of the 14th June was when we saw our first group of juveniles of this year. Two Swifts circled the house, flying low and close to the nest boxes while our two were still inside. We later saw a group of five, although our box was empty and so the group may have included our birds. This was the first sightings of any Swifts other than ours since early May.