(Reproduced from The Eider – December 2020) Annette Anderton
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Arrivals
After a successful year in 2019 with two pairs of Swifts breeding and another pair prospecting for a nesting site, I was looking forward to the return of our Swifts in 2020. Our roof was in need of repairs so we had arranged for the work to be done in April before the Swifts arrived. At the end of March the scaffolding was erected (Fig. 1) and then two days later the whole of the country was in ‘lockdown’ due to coronavirus!
I was horrified as I had read that scaffolding can inhibit Swifts from entering their nesting sites ( Concern For Swifts, 2002) and knowing that Swifts are protected under the Wildlife and Countryside Act (1981), which makes it illegal to knowingly destroy or disturb the nest site during the nesting season, it was with some concern that I waited for the Swifts to return.
Luckily, the Swifts had not been told about the travel restrictions and on 5th May I spotted my first Swift of the year circling over our house. Then, on the 7th May at 7.30 am, there was the familiar sound of screaming as two Swifts flew towards and across the front (SE side) of the house. This continued until about 9.30 am but I was upset to observe that they regularly veered away as soon as they reached the scaffolding. However, at about 9.45 am they flew through the scaffolding and started ‘banging’ one of the boxes and at about 11.45 am they entered this box and spent the whole afternoon in and out of the box and, to my relief, seemed not to be at all concerned by the scaffolding (Fig. 2).
The date of arrival of the first of our Swifts was one day earlier than that observed last year (dates of arrival in Kilmichael Glassary have ranged from 1st-9th May between 2017 and 2019 (Anderton, 2020)). Swifts were first observed in Oxford in 2020 on 27th April (range from 4th-7th May, 2017-2019) and in Bristol on 23rd April (range from 20th April-1st May, 2017-2019) (Anderton, 2020).
Interestingly, in 2018 Lack discussed the fact that from 2014-2017 the first Swifts arrived at the Tower in Oxford on the 4th or 5th May which was an average of 9 days later than arrival times, ranging from 24th-29th April, between 2007-2013 (Lack, A. 2018). He suggests that deteriorating weather conditions over this period of time may have had an effect but also points out that various activities at the Tower may also have had an impact. It will be interesting to see if their earlier arrival (27th April) in 2020 is repeated in 2021.
Our two Swifts arrived two days apart which is in line with the observation by Lack (1956) that
breeding pairs separate in the autumn and re-join in the Spring. In a four-year study Lack (1956) reported that in over three-quarters of the pairs the two individuals returned on different days (range 1-21 days).
Most of the time for the next couple of weeks I only saw two Swifts entering and leaving the box and sometimes ‘banging’ the box, the house wall and window behind it and parts of the scaffolding. Occasionally a third Swift would join them.
Then, on the 21st May, five Swifts started circling over the house and flying and screaming around it, and two Swifts entered the hole under the eaves of the NE gable-end of the house where Swifts had bred successfully in 2019.
Meanwhile, in the box on the front of the house which the non-breeders occupied last year (Anderton 2020) and in which a Great Tit had roosted all winter, there had been frantic activity with a pair of Great Tits building a substantial nest in one day(!) on the 26th April with nestlings starting to hatch on the 19th May. We were watching this nest with some concern and hoping that the Tits wouldn’t be evicted by the returning Swifts. But, to our delight, the Great Tit nestlings fledged on the 8th June and then on the 22nd June a male and a female House Sparrow came into this box and started rearranging the nesting material. As there seemed to be no sign of the non-breeders arriving, I assumed that the next family emerging from the box would be Sparrows.
However, on the 4th July, without any dramatic encounters, a single Swift appeared in this box and on the 8th July was joined by a second Swift. This pair made very desultory attempts to add a few bits of grass and feathers to the nesting material but spent most of their time feeding, preening and sleeping. So, it would appear that this was our pair of non-breeders back again as non-breeders seem to return later in the season than the breeding Swifts (Lack 1956).
Both breeding pairs of Swifts were successful in raising their chicks. Details of this will be reported in the spring edition of ‘The Eider’. But events at the end of the season proved to be interesting so I shall now discuss this in more detail.
Departures
On the 5th August, as the light faded, the older of the two nestlings in the front of house box, which was fitted with a camera, spent a lot of time peering out of the nest entrance (Fig. 3). Then, at 9.38 pm, it tipped down into the entrance and dropped out immediately and I was able to see it make its first flight. The second nestling remained in the box being fed by its parents until the 8th August when it also fledged at dusk. It had a number of abortive visits to the nest entrance where it tilted forward into the hole but then scrambled back, breathing heavily, and then did some wing exercises. Finally, it tipped forward into the nest entrance but, unlike its sibling, it didn’t leave immediately but seemed to be attempting to hold onto the box as if it had changed its mind, and I could see its wing feathers poking up inside through the hole as if it was trying to hang on. But at 9.59 pm it disappeared from view. Its exit was similar to one reported by Bromhall (1980) which “left at last … but not without a final moment of panic … it tipped forward …too far to turn back …with most of its body outside it clung upside down by one foot, a wing tip braced across the entrance … after a few seconds it let go and plummeted into space.”
Our nestlings fledged at dusk whereas Lack (1956) and Bromhall (1980) both reported that most nestlings in Oxford fledged early in the morning. Perhaps our nestlings left under the cover of dusk/dark to avoid the attentions of the pair of buzzards frequently seen circling over our house in daylight hours?
Once the nestlings had fledged their parents continued to occupy the box, regularly returning each night. Reading the reports from Oxford and Bristol I noted that in both cases it appeared that the statement that “it’s all over” may have referred to the departure of the final nestling (O.U.M.N.H 2020 /Glanville 2020). In fact, on the 7th August 2020 Glanville stated that “There are still 6 adults here … but now that the last chick has just gone I expect them to leave today”, but there is then no mention as to when these adults actually did leave.
Lack (1956) commented that the parents normally remained after their broods have left. The number of days they stayed was affected by the weather over the summer. Thus, after wet summers, they would stay for an average of between 8-11 days (but one pair stayed for 26 days). However, in fine summers the average was 2-3 days after their brood fledged. He suggested that they stayed so that they could feed and rest and put on fat to act as a reserve on their long journey south. This fits in with the fact that Swifts leave later after bad summers when food would have been less plentiful both for them and the nestlings they were feeding.
Bromhall (1980) also drew attention to the fact that in Oxford the quality of the food available to them decreased at the end of the season. So, meals sampled in July and early August contained very few beetles (Coleoptera) whereas in one sample obtained at the end of August, out of 348 insects, 106 were beetles. Coleoptera means ‘sheath wings’, and most of their weight is made up of indigestible chitin. However, in Scotland, particularly in Argyll (!), there are vast populations of midges right into the early Autumn. Could it be that, although they are normally found close to the ground, they may possibly be carried up in air currents to the height at which Swifts collect their food and provide more nutritious food later in the season?
It was noticeable in Kilmichael Glassary that when their chicks fledged both of the parents in the box with the camera looked a bit out of condition. Their feathers lacked the sleekness of earlier in the year. But it was worrying that one bird also looked particularly slow in its movements around the box. From when the second nestling left, both parents spent their days coming in and out of the box, staying out for longer when the weather was good but regularly returning to the box and/or remaining in the box when it was raining (Anderton 2020). When in the box there was a lot of mutual preening and wing exercises. During August there were frequent screaming parties of between 5-12 birds.
On the 29th August (high pressure over UK, a dry and sunny day with NW winds) both Swifts left at 7.58 am but only one returned that night. Compared with its mate this bird was still in poor condition and I noticed that on the first couple of nights after its mate left it was very restless and during the day it came in and out of the box many times. Similar activity was recorded by Lack (1956).
The weather deteriorated over the next few days and the remaining bird could not get out to feed so much. When in the box it spent a lot of time preening itself and regularly did wing exercises (Fig. 4). Most of the time its presence was now much less obvious as it slipped in and out of the box in silence, so without a camera in the box it would be easy to think that it had left.
We were in the garden at dusk on the evening of 3rd September, not having seen any other Swifts since 29th August, when at least 3, and probably 5, Swifts circled round high over our house. I couldn’t definitely confirm that there were 5 as we were trying to finish laying some concrete and I didn’t have my binoculars with me! Then, at about 7 am on 4th September, I saw 2 Swifts flying in an easterly direction up the Glen. Were these Swifts from further north passing over our house as they migrated south, or were they birds from the local area that had been roosting in their nest sites building up their fat reserves prior to migration?
Throughout the next week the weather was wet a lot of the time, but there were some spells of warm sunshine, and the single Swift came in and out of the box frequently and did a lot of wing exercises. Its plumage was now much sleeker and it was moving around the box with as much ease as Swifts ever do.
On the 9th September the weather improved, it was lightly overcast and there were NW winds. The Swift left at 8.49 am and didn’t return, so hopefully was safely on its way to Africa. Lack (1956) observed that, on average, a quarter of the pairs of Swifts left on the same day, half left within one day of each other, but the difference in departure date could be as much as 14 days. For the Kilmichael Glassary pair the difference was 11 days, but it should be noted that the last adult Swift left 32 days after its younger fledgling. In Oxford most departures also occurred in the morning and the date of departure was significantly affected by weather conditions (Lack 1956).
The non-breeders also stopped roosting in their box on separate days. On the 7th August at 6.38 am both birds left the box but that night only one bird returned. This bird returned to the box every night until the 13th August, when having left the box at 6.41 am it didn’t return that night. Over this period of time there were regular screaming parties of between 5 and 12 Swifts, so it is possible that the first non-breeder to leave the box spent the subsequent nights roosting aerially prior to departing for Africa but this is difficult to prove, and it may have left to fly south immediately.
Non-breeding Swifts are known to roost aerially in breeding areas, it is referred to as the ‘Vespers flight’. Lack (1956) observed mass ascents of Swifts at twilight and Bromhall (1980) reported that observations by First World War pilots and subsequent radar studies had shown that Swifts fly up to as high as 2500 m at dusk and come down at dawn. A detailed study of Swifts fitted with micro data loggers by Hedenstrom et al. (2016) confirmed this.
The departure of our last Common Swift on the 9th September may seem late but it should be noted that in 2016 the last Common Swift left Bristol on the 9th September and in 2019 the last one left the Oxford Tower on 14th September. Single Swifts were observed over Balnahard Bay, Colonsay on the 3rd September 2020 (David Jardine, personal communication) and Machrihanish, Kintyre on 22nd October (by Caroline and Bill Anderson, Jim Dickson, personal communication).
Also, sadly, on 23rd October 2020 a dead first year Common Swift was found in a garden in Ardrishaig (by Alan Dykes, bird dead for approx. 2-3 days, Jim Dickson, personal communication). It is possible that this was a late migrant (local or from further north) that got caught out by one of the very bad rainstorms in October, as it has been reported that migratory Swifts caught out by cold and/or wet weather, with no nest places to shelter in and no flying insects to eat may cling to any structure (house wall/window frame/tree) to rest and try to get protection from the cold and wet. Sadly, many of these Swifts die of starvation and/or hypothermia.
In a very interesting study of migration patterns of European Common Swifts, Akesson et al. (2020) found that birds breeding to the south, in Spain and Italy, migrated approximately one month earlier (range 3rd July-8th August) than the most northern population in Swedish Lapland (range 7th August-9th September) and the southern breeding Swifts were therefore able to secure the most favourable wintering areas furthest to the south in Africa. This phenomenon, known as chain migration, is very rare in migrating birds, the usual pattern being leapfrog migration where northern breeding birds winter furthest to the south. And if we think that our Swifts have a long way to go when they migrate to Africa, an average of 7800 km for UK Swifts (Akesson et al. 2020), then spare a thought for the ‘pekinensis’ race of the Common Swift (Apus apus) which travels more than 13,000 km from Beijing to spend the winter in Southern Africa (British Birds 2015).
Finally, reports of late sightings of Common Swifts should always be treated with caution as in autumn Pallid Swifts can be driven up into the UK from the Mediterranean by strong southerly airflows e.g. in early November 2018 the passage of ex-Hurricane Oscar resulted in an influx of at least 30 Pallid Swift, 6 Common Swift and one Little Swift to Britain (BTO 2020). Differentiating between Pallid and Common Swifts is dependent on very subtle differences in plumage, not easily observed with a fleeting view of the bird in flight (Jim Dickson, personal communication).
But, it is also important to stress that in late summer and autumn it is still worth looking out for Common Swifts that may be roosting locally and going out daily to feed to prepare themselves for their long flight to Africa.
References
Akesson, S. et al. (2020) Evolution of chain migration in an aerial insectivorous bird, the Common Swift Apus apus. Evolution 2020: 1-15 https//doi.org/10.5061/dryad.cz8w9gjlw
Anderton, A. (2020) Living with Swifts. Eider 132: 14-17.
British Birds (2015) Mystery of ‘pekinensis’ Swift migration revealed. British Birds 108(6); News and Comment.
Bromhall, D. (1980) Devil Birds: The Life of the Swift. Hutchinson, London.
BTO (2018) Birdtrack, Influx of Pallid Swifts https://www.bto.org/our-science/projects/birdtrack/2018-influx-pallid-swifts
Concern for Swifts (Scotland) (2002)
https://concernforswifts.com/advicenote.html
Glanville, M. (2019) Bristol Swifts 2020 Blog.
Hedenstrom, A. et al. (2016) Annual 10-month Aerial Life Phase in the Common Swift Apus apus. Current Biology 26: 3066-3070.
Lack, D. (1956) Swifts in a Tower. Methuen, London, UK, (reprinted in 1973, Chapman and Hall, London, UK).
Lack, D. (2018) Swifts in a Tower. Unicorn, London (full reprint of the text of the 1956 edition with new photographs and an additional chapter by Andrew Lack updating the work carried out between 1956 and 2018).
O.U.M.N.H. (2020) Swifts Diary, Oxford University Museum of Natural History, https://www.oumnh.ox.ac.uk/swifts-diary
Wildlife and Countryside act (1981) https://www.legislation.gov.uk/ukpga/1981/69/contents