Swifts diary

The colony of swifts that nests in the Museum tower has been the subject of a research study since May 1947. It is one of the longest continuous studies of a single bird species in the world, and has contributed much to our knowledge of the swift.


2 May 2023

The swifts are early this year. We normally see the swifts arriving between the 5th and 8th May but this year there were two birds sitting in boxes today. This could indicate a good start to the season.


8 May 2023

The weather has not been particularly warm or dry but the swifts seem to have settled in quite quickly. Today there were 8 birds sitting and evidence of a further 8 nests with signs of nest refurbishment, fresh feathers and droppings, nest building and cleaning.


15 May 2023

This was a cold clear day with no rain. There are 22 active nests with 13 eggs visible. Only 2 adults and 1 pair were sitting in the boxes and the tower was unusually quiet. It is possible that the swifts are out feeding somewhere and will return soon.


22 May 2023

Another cool overcast day but much more activity with swifts screaming around the tower and birds in the boxes responding. There were nine adults sitting and another nine pairs in the boxes. Inspection of the boxes revealed at least 23 eggs which, when added to the eggs known to be there last week, gives a total of at least 32 eggs and signs of activity in about 37 of the boxes.

Birds are still arriving and we expect the counts to grow next week. The critical time that determines whether the breeding season will be successful, average, or poor is the weather during the last week of May and the first week of June. We shall see what happens!


28 May 2023

Today was bright but with a bitterly cold east wind, very little swift activity was to be seen around the tower; just an odd lonely swift making a half-hearted call.

Inside the tower it was also very quiet – worryingly so – but nest checks still needed to be carried out. It was pleasing to find out that most of the boxes were occupied. There are 38 boxes either occupied or showing signs of activity. Of these, 28 were occupied by pairs, many with eggs, and another seven boxes had incubating adults sitting on the nest. It was notable that all the boxes on the east side of the tower which were occupied held a pair of birds snuggled tightly together. Lone adults were mainly on the west side.

It was not all good news in the colony, however. Six boxes which had appeared to be active now seem abandoned. These may be inexperienced birds practicing nest construction. One of these nests did have a single egg in it last week — this egg has disappeared. Another nest holds a single cold egg. It may be that the birds will return and complete the clutch, but we shall have to wait until next week and see what happens.


5 June 2023

Another cool Monday morning with a cold wind blowing; there was very little flying activity around the tower and hardly any sound to be heard from the colony.  

Inside was a cause for concern; 7 of the 47 previously-occupied nests had had their eggs ejected or been deserted. Of these 7, 4 nests had eggs ejected (8 in total) and 3 had been deserted entirely. Occupants of 5 other nests either had not laid eggs yet or were delaying until the warmer weather arrives. This leaves 35 active nests containing eggs.  

All is not bad news though; there were 32 adults sitting tight and a pair sitting in another box. In addition, 2 new boxes held warm eggs so we still have 35 active nests.

With birds sitting tight and incubating it is not possible to make an accurate egg count as swifts are prone to desert if disturbed this early in the breeding cycle. However, from a combination of what we have seen so far it is possible to be sure that a minimum of 55 eggs are being incubated and theoretically there is potential for between 70 and 100 eggs to be the actual total if each bird is sitting or either 2 or 3 eggs which is the normal clutch size. We do have one bird which has laid 4 eggs, this is unusual although last year she laid 4 as well but only 3 hatched.

Eggs should start to hatch during the next 2 weeks and it will then be possible to get an accurate count.  

12 June 2023

After a weekend of extreme thunderstorms and temperatures of 30 degrees C, the colony was very active today with many birds on the wing and screaming around the tower. Inside, it is hotter still and there is lots of activity. We now have 41 active nests with our first young, visible eggs, or birds sitting. Overall, 29 young were visible, many of these recently hatched and naked and blind. There are also twelve already covered with their first visible downy feathers. Ten further eggs were visible, but in 19 boxes the adults were sitting tight, covering whatever young or eggs that lay beneath them. If each of these sitting birds has the average clutch of three eggs, and all these, plus the 10 other eggs observed, hatch and the young fledge, we could expect a maximum of 96 new swifts fledging this year. Much depends on the weather and the supply of insects, as well as the experience and parenting skills of the adults. Four eggs had been kicked out of the nest this morning and were gently replaced. As a tenet of natural selection, it is worth remembering that not all young survive and so 96 fledglings would be truly remarkable and a very successful year.

19 June 2023

After another very hot week of thunderstorms there was some relief today as temperatures dropped slightly and a welcome fresh breeze cooled the nest boxes. 42 boxes were active with 39 adults sitting tight on eggs or young, making counting them a little tricky. By using the previous weeks' data, adding in observations from today, and counting discarded eggshells as a guide to what the adults might be concealing, it looks as if there are at least 21 eggs still being incubated and around 36 young either visible or underneath an adult. The young counted last week are developing quickly and, looking at the earliest to hatch, it is hard to imagine how they ever fitted into such small eggs!


26 June 2023

The hot dry conditions continue although the wind is still strong. There are swifts flying around the tower and calling. Inside the nesting colony the sound of chicks contentedly making a winnowing sound can be heard. There are now 43 active nests and 37 of these have at least one adult present.

A total of 79 young can be seen plus 9 or more eggs still to hatch. These are minimum figures as there are adults sitting tight and this makes it difficult to see what they are covering without disturbing them — it is not worth the risk of causing birds to desert as whatever they are covering will become clear in time as young grow larger.

The age spread of chicks is interesting: some are just hatching, while today five fully-grown chicks were ringed and, of course, there are adults who still have eggs.


3 July 2023

This week there has been a change in the weather; a cold wind is blowing and it's damp with showers. All is not doom and gloom, however, as we have 44 active nests and at least 86 chicks in the tower. Of the 44 nests, 4 are second attempts, so we still have 9 eggs — although some hatched during past week and others have been laid.

Two adults from previous years have been identified from their rings and another adult has been ringed. A further 29 chicks have reached a size where they can be ringed. This is a mixed blessing because, although it is good to see the chicks growing so well, it is sad to think that they will soon start to depart for the winter in Africa and we will see very few of them again. About one in a hundred youngsters ever return to the tower, although the adults return every year.


10 July 2023

The weather was much milder today. A few adults were noted around the tower but little screaming was heard. Inside the colony, a few young could be heard winnowing, as well as the occasional thump of an adult returning to the box with food. This is always followed by a noisy free-for-all as each youngster attempts to get fed first.

The sad news is that one chick has died. On the other hand, we now have 90 healthy chicks at various stages of growth, from newly hatched little pink lumps through to fully developed large chicks which can only be told apart from the adults by the silvery edges of the flight feathers.

One chick that was ringed on 3 July has set off for Africa already. It is always bittersweet when birds start to fledge. On the one hand, it is another successful chick setting off to seek its fortune but, on the other hand, it heralds the season starting to come to a close with the birds soon to be gone and the tower becoming silent until the next summer.

On a happier note, the hatchlings will be with us for another 6 to 7 weeks so there is still plenty to look forward to!


17 July 2023

The weather this past weekend was interesting, to say the least. Strong winds and heavy rain led to a cold, miserable three days for the swifts. This has been reflected in the colony. All of the young which hatched during the past week died of cold and/or starvation, nine chicks in total.  

Happier news is that 26 chicks fledged and are on the way to warmer climes around the south of Spain. This leaves 36 active nests containing 69 young and one nest with two warm eggs. Some of these chicks are large and ready to fledge, whilst others are only about two weeks old. 

We were visited today by Hannah Bourne-Taylor, the author of Fledgling, who is currently campaigning for the inclusion of ‘swift bricks’ in new build housing. She has brought her case to Parliament and has several senior MPs backing her cause.  

Few birds were flying around the tower, but the forecast weather this week is warmer with occasional light showers and this is weather the swifts seem to enjoy, with lots of flying insects to feed to the young. A food ball which was regurgitated by one of the adults seemed to contain a lot of small pollen beetles and weevils, as well as small plant bugs. This mixture seems to be a favoured food for the young, as food balls from previous years have shown.


24 July 2023

The cold wet weather continues but young swifts are fledging and heading off to warmer weather on their way to spend the winter in Africa.

We still have 24 active nests containing a total of 43 chicks but so far at least 38 have left. To date, 79 chicks have ben ringed and a further 9 remain unringed as we only put the ring on about a week before the young are ready to leave the nest.

The camera has been moved as the nest it was monitoring is empty due to the young fledging. It has now been put onto a box with other young birds and will be moved again to a nest with even younger birds next week.


31 July 2023

A silent melancholy hangs over the tower today with just an occasional swift call. Many of the chicks have fledged and the adults are also departing. We still have 11 nests active with 18 live chicks waiting to depart when the time is right.

Once again, the cold wet weather has taken its toll and today 2 more dead chicks were found. The wet and windy conditions have made foraging difficult for the adults and the cold has also affected the remaining youngsters.

Nature is not all butterflies and fluffy bunnies so we have to accept that not all chicks will make it. On the happier side, we have already sent almost 60 healthy chicks off to Africa and have nearly 20 more to go so it has been a very successful breeding season despite the casualties caused by the weather. Let us hope the weather is a bit warmer and drier in the coming weeks to give the remaining young a chance to fledge.


7 August 2023

Today is cloudy with a light breeze; it's mild and dry so should provide plenty of insects for the swifts. In the tower colony there is little sound, just an occasional clunk as an adult arrives with food for the few remaining chicks. This is followed by scuffling and wittering as the young beg for food.

There are 11 chicks still in the 9 active nests and they are quite large now. I expect many of them will leave in the next few days. The camera has been moved again but I suspect the chick will fledge soon.

Once again hatching has been successful with only about a dozen eggs failing or thrown out. But survival of young, especially from late hatchings, has been poor due to the cold wet days in July. All is not lost though as a record number of swifts have survived.


14 August 2023

In a word, Monday was wet. The miserable weather was the reason that there was very little activity or sound from the tower and it was a concern what might be found in the colony.

Thankfully there were still 5 occupied nests with just 6 fledglings remaining. Most of these are well grown and almost ready to leave but there is also one smaller chick that will need another week or tow before it is big enough to leave the nest.

There is a forecast of warm dry weather for the next week so it is looking hopeful that all will survive to take the long journey to Africa.


21 August 2023

Only 2 chicks remain!

One of these looks as if it is getting ready to leave during the week. Warm weather and a good feed is all it will need to encourage it to go. 

The other chick has now been ringed and should leave during the next 10 to 14 days – we shall see!


29 August 2023

Climbing the tower today was a quiet and slightly mournful experience as only one bird remains, diligently exercising by doing push-ups on its wings to build up its flight muscles and reach its optimum flight weight. The adults have long since departed and this lone bird will be off to follow them in the next few days, launching itself from the safety of the nest box and flying nonstop on its 7000 mile journey to southern Africa before returning to England next May. Flying up to 300 miles a day, eating and sleeping on the wing, it won't land again for at least the next three years when it will be mature enough to start its own nest. Although ringed, we may never see this individual again as only around 1 in 100 birds ringed as a juvenile ever return to the same site they fledged from. Next week will therefore probably be the last Swift's Diary entry for 2023 and it looks like it has been a good year overall. Make sure you check in to see the final numbers of chicks successfully raised and fledged from the tower!

4 September 2023

It’s over for another year; the last chick fledged during the weekend and is now off to Africa on a journey that will take it south along the Atlantic coasts of France, Spain and Portugal, then across the Mediterranean Sea and across the Sahara Desert into West Africa. The second leg of its journey will be eastwards to the Congo rainforests and the Great Rift Valley where it will spend the winter before heading west again to start the long flight north to Europe.  

The summer of 2023 has been a good one for our swift colony. There were 114 eggs laid, of which 101 hatched. All was looking good until the cold wet weather in July which caused the deaths of a dozen newly hatched youngsters due to the cold and the lack of insect food.  

On a more positive note there were 57 nesting attempts of which 44 were successful and 86 young fledged, this is the biggest total since 2008 so certainly worth celebrating. (Mine’s a Gin & Tonic). This has happened mainly due to the warm June weather and is particularly welcome in view of the construction work which has been happening here, but which did not seem to be close enough or loud enough to cause concern to the breeding birds in the colony. It was also good that they did not have to contend with a Sparrowhawk this year.


The average numbers of young swifts ringed each year over the last 50 years are:


1963–72: 36.7


1973–82: 70.4


1983–92: 100.0


1993–2002: 99.2


2003–12: 81.1