Many of us at the Museum are inspired creatively, as well as scientifically, by the wonders of the natural world. So it is always uplifting to see that the Museum building and its collections evoke similar feelings in our visitors. However, apart from the odd, sneaked peek over the shoulder of someone busily sketching a specimen or spandrel, it is rare that we get to enjoy the results of their inspiration, which is why it was so nice to receive the poem below from Tony Owen.
Tony emailed us to say that, whilst teaching on the Summer International Programmes at Hertford College in 2018 and 2019, he often visited the Museum and became aware of the colony of swifts that annually nests in the Museum tower. Tony read about their fascinating lives, watched their progress through the breeding season on our live nest box cams and Swifts Diary, and enjoyed seeing them screaming around the tower itself.
This led to the inspiration for Tony’s poem – The Swifts. In putting pen to paper, Tony joins many other poets who have found inspiration from these amazing birds, including Ted Hughes, Anne Stevenson and Wilfred Owen.
It was very kind of Tony to share his poetry with us so we thought we would share it with you in the hope that it may inspire your own creativity from nature.
Last week’s observations of the swift nest boxes in the Museum tower highlighted the drama the colony faces in the struggle for survival. This week’s survey made that struggle even more explicit…
Clambering through the darkened spaces of the Museum tower, lit faintly by the red lights that the swifts cannot see but which help give surveyors a dim view of the ladder rungs and observation platforms, I peered briefly into each nest box to count the birds and eggs.
In one box I came across a dead bird, alone and lying on its back. Carefully bagging up the body for later investigation I continued my count while pondering the cause of its death, the sadness relieved slightly with the discovery of new eggs in other boxes and the promise of new life to come.
Screams and banging from birds prospecting for nest sites are a regular backdrop to each survey. Birds call and swoop past the boxes only inches from my ears, separated by just a few roof slates. The birds within scream back in answer. But on this occasion, half way down the tower, I became aware of particularly loud and persistent screams and banging, coming from within a box.
A quick peek inside revealed a hectic struggle between at least three swifts, wings drawn back, wrestling and rolling around, pecking and slashing at each other with their sharp claws. It was actually impossible to see if the fight involved three or four birds as the struggle filled every inch of the small box with wings, beaks, claws and feathers.
David Lack first documented these fights in his excellent book Swifts in a Tower. He proposed that they were the result of birds entering an already occupied box in the struggle to find a suitable nest site.
Sitting and anxiously listening beside the box, I recorded the fight lasting 15 minutes from the time I became aware of it. Lack documented ‘gladiatorial shows’ that lasted five and three quarter hours; they were painful to watch, he admitted, as the swifts have a surprisingly strong grip and claws capable of drawing blood, but rarely resulted in death.
When the noise died down, I gently lifted the cloth blind to take another look. Only two birds remained, both looking exhausted and fiercely gripping each other’s feet, one lying under the other. A quick flurry and the upper bird disengaged and jumped from the nest box entrance.
Lack also mentions in his book that it is usually the bird underneath in these struggles that is the winner and I was relieved when the remaining bird picked itself up and returned to the two eggs, which had somehow remained in the nest, settled on top of them and preened itself. This suggested that the nest’s original occupant had won, driving off an intruder.
The screaming and banging outside the boxes is a check for a screamed response from within. It reveals whether a box is already occupied or empty, before the bird risks entry. Presumably, the fight I witnessed was the result of a bird not hearing a response or perceiving it as coming from another box.
The drama of the fight illustrates the incredible importance of nest sites and the fidelity the swifts have to them after a year on the wing. Nest sites are at a premium and swifts are almost totally dependent on nesting in old buildings as there are so few forests with suitably old, cavity filled trees remaining.
Once a nest is occupied the owners will fight furiously to defend it and David Lack did record occasional incidents of birds fighting to the death. So perhaps this was the cause of the dead bird I had found lying on its back, but that will have to wait for a later examination.
It is important to record nest sites and, if you can, put up nest boxes. RSPB’s Oxford Swift City project, which the Museum and Oxford City Council were involved in, annually surveys and records nesting sites so that development in these areas is restricted during the breeding season and developers must include plans to protect and provide new nest sites when repairs to property or new building takes place. If you would like to help with the work of conserving one of the most dramatic annual migrants to our shores visit the RSPB site.
With the noises of the hectic morning commute temporarily silenced, it has never been a better spring to enjoy the sounds of the dawn chorus. If you are able to get out early it’s a great way to reduce some of the stresses of lockdown. But if you can’t, or would rather have a lie-in, here we bring a little of the dawn chorus to you.
The video above shows the beautiful grounds of Harcourt Arboretum, a site a few miles outside Oxford that is part of Oxford University’s Gardens, Libraries and Museums. The chirruping, tweeting soundtrack was recorded at the start of the pandemic lockdown, and is an excerpt from 50 minutes of uninterrupted dawn chorus which you can listen to in full here (recommended background while WFH!):
The enveloping sound of the dawn chorus is an ensemble piece, but who are the individual players? To hone your birdsong identification skills and practice picking out individual songs of some common British birds, Andy Gosler at the Edward Grey Institute for Ornithology has put together this beautiful resource.
So now we’re in the zone, let’s find out a little more about the dawn chorus and how it’s made.
A sense of dawn Why are so many birds singing at dawn and not at another time of day? There are several good reasons which may explain this.
At dawn, there are fewer other environmental noises cluttering the airwaves and the air density and temperature allow sound to travel further. Many migrant birds arrive in the UK overnight and early morning, and those that are ready to breed begin looking for mates and territories early in the day. So singing at this time stakes a clear claim to new arrivals and announces that the territory is already taken.
For insectivorous birds and those that use sight to find food, dawn is the least profitable time to search. Insects are more dormant in colder temperatures and food less easy to spot in dawn’s lower light levels and early morning mists. It’s a better use of time and energy to sing!
But why spring? What triggers birds to start singing? It clearly makes sense to breed at this time of year when there is a steady supply of food, as insect population growth coincides with the re-growth of the plants that feed many insects.
But the real trigger is day length. Increased light boost hormones in birds that spark incredible physiological changes. Unlike humans, birds have an amazing ability to reduce and increase the size of various organs according to their use, carefully regulating the amount of energy expended by those organs.
Shifting sounds As hormone levels increase, not only do birds’ sexual organs increase in size ready for the breeding season, but the part of their brains dedicated to sound processing and sensitivity also increases, meaning that birds’ hearing abilities fluctuate throughout the year.
Imagine not being able to recognise what people were saying or who was talking in winter, then suddenly being able to pick out every minute difference in tone, volume and timbre in spring! When you listen to the cacophony that is the dawn chorus, this is exactly what each bird is doing – recognising each individual and its territorial and breeding condition – and many birds show less acuity for this outside the breeding season.
Sound location also improves. Humans have relatively large, wide heads and this allows us to judge the direction a sound is coming from by detecting the slight differences heard by each ear. With their tiny heads, birds cannot do this when their heads are still, so they move their heads around a lot to help locate sounds.
You might be thinking that with such sensitive hearing birds would be in danger of going deaf during a raucous dawn chorus. But they have another adaptive trick up their sleeves. Inside the inner ears are tiny cilia, or hairs, that detect the vibrations of sound. In mammals, these hairs gradually diminish over time and don’t grow back, but birds have the ability regrow cilia throughout their lives!
Hidden music Birds are also able to process birdsong much more quickly and fully than we can, hearing things that our brains are just too slow to cope with. Whilst we may love the musicality of the dawn chorus, we are actually missing many of the individual notes.
Sonograms of bird songs show that where humans often hear just a couple of notes there may be several more emitted at rapid speed.
How do they do it? We sing by passing air over flaps of skin in our sound-producing organ, the larynx, a bit like blowing over a piece of grass trapped between your thumbs. But birds have separately evolved another and more impressive way of singing. They don’t just have one organ to produce song, they have two – called syrinx.
Syrinx are more like drum skins that can be tightened or loosened by muscles as sound passes over them. They can be operated independently or together enabling a single bird to sing a chord of several notes at the same time in harmony with itself!
Time to tune in to the dawn chorus and marvel at the complex, beautiful phenomenon of birdsong…
We have our first eggs! After an earlier than usual return from the warmth of Africa, followed by a cold snap of north easterly winds, our swifts have begun to lay their first clutches of eggs in the tower.
Ten eggs were counted on 14 May, some in pairs and some lying singly on nests. Birds in other nests appear to be incubating as well, sitting in pairs and screaming out at any newcomers investigating possible nesting sites.
More swifts are arriving daily and screaming parties are urgently exploring for potential nesting locations. They buzz the tower’s nesting holes at speed and bang on the entrances with their wings like naughty teenagers playing a vociferous game of ‘knock and run’!
Typically, no bird has yet elected to nest in either of the boxes fitted with webcams. But as the weather warms and more swifts take up residence every day, we’re sure you’ll be able to follow all the drama of the Swifts in the tower very soon.
The delicate art of laying
Swifts tend to lay their eggs in the mornings, usually between 8am and 11am. The small, fragile eggs are white to reflect light, an adaptation shared by most cavity-nesting birds that makes the eggs more visible to adults in the dark of the nest.
The first eggs this year appear to be quite early in the season compared with the observations by David Lack in the 1940s and 50s. At that time, when the study of the Museum’s colony began, the first eggs were recorded on average between 17 and 22 May, but sometimes none was laid until the first week of June.
Egg production and laying in swifts are very closely tied to the weather, and production seems to be triggered by the availability of food. Swifts feed exclusively on small airborne insects, which are more abundant in the warm thermals and light winds we experience on good summer days.
It takes a swift five days to produce and then lay an egg. Five days before our first eggs were laid it was sunny and warm, just before the strong, cold north easterly winds swept down over the weekend and lowered the temperature. The warmer early start to the summer seems to have triggered this early laying; whether this is a trend that is increasing as the climate changes is something we should able to answer with long-term datasets provided by studies like this.
Dealing with the weather Whatever climate change has in store for us it is becoming clear that we won’t experience repeated hot summers. The unpredictability of the British summer reigns supreme.
Swifts have evolved several wonderful adaptations to deal with the vagaries of our weather. Their eggs can be left without an adult to keep them warm for several days. There are records of eggs being left unattended for almost a week and still developing normally. Although adults usually take it in turns to feed and brood the eggs, sometimes during the day the eggs are left unattended by both birds which are then able to forage far afield for food.
Unlike many songbirds which produce one egg a day until their clutch is completed, swifts are able to space out their laying. In a clutch of two or three eggs, the second or third may be laid two or three days after the first, depending on weather conditions. The birds will also limit the size of clutches, with clutches of three eggs the average in warm weather and two eggs the average in cold weather. This helps the adults to supply all of their young with enough food.
Finally, swifts may also eject eggs and lay a second clutch. Some studies have linked this behaviour to cold weather but this has not always been the case at the Museum colony and is a further line of investigation in the ongoing studies of these most secretive of birds.
From laying to hatching usually takes about 19 days, depending on the weather. So we should be seeing our first chicks at the very beginning of June, hopefully streaming live on the Swiftcam…
Screaming parties prospecting for nest sites are a good way for you to see if you have nesting swifts nearby. Any records really help with our understanding of the current population in the UK. You can help conservation and recording for the Oxford Swift City project, or use the RSPB’s Swift Mapper for the rest of the UK.
‘Look! They’re back! Look!’ This line from Ted Hughes’ excellent poem Swifts shares the excitement generated every year by the arrival of one of the most iconic summer visitors to Britain…. and I’m pleased to announce that they’re here!
Each year at the Museum we eagerly look forward to the swifts returning from their epic migration to southern Africa and back to our tower. Here they will land for the first time in a year, to nest after a 14,000 mile journey on the wing.
Necks of Museum staff are strained as each of us develops a twitcher’s twitch, heads snapping upwards at every bird flying overhead. We all hope to be the first to see a swift returning to the buzz the tower, scoping out the possible nesting opportunities, some no doubt remembering past sites from summers gone by.
With the Museum currently closed due to the global pandemic, this year most staff will be craning their necks to the sky at home, perhaps wondering if any swifts they spot are ‘our’ Museum swifts, or some of the many others that colonise the roof spaces and nest boxes of Oxford and its surrounding towns each year.
The swifts at the Museum are part of what is probably the longest-running continuous study of any bird colony in the world, started by David Lack in 1948. Because so little is known about these protected and declining populations of birds, every bit of data matters.
Although the Museum’s Swift Warden, George Candelin, is currently unable to reach the Museum during the lockdown, we agreed that it was an essential part of our role as a conservation and research institution to continue the study that has helped us to understand what little we do know about these enigmatic visitors.
Even before the swifts arrive there is a lot to do. With George’s expert guidance, in the last week of April we climbed the winding stone staircase and then the ladders to the very top of the tower to prepare for the swifts’ arrival.
Each of the nest boxes is thoroughly cleaned and their entrance holes dusted to make sure they are free of cobwebs or other obstructions. We then replace the shallow nests used to entice nesting activity. Swifts cannot land to collect nesting material and so have to collect suitable airborne material while on the wing. Their nests are often scanty, basic affairs made of a few stray feathers and other random bits of material they have found blowing about in the wind, so they seem to appreciate a helping hand.
Each of the man-made nests comprises a shallow ring of soft feathers. This is removed from the nest box at the end of each breeding season, frozen to kill off any resident feather lice or other pests, then thawed and gently replaced.
Finally the Swift Cams are put in position and checked, ready to beam intimate shots of life in the tower directly into your home. Now you can follow the breeding season of these fascinating but hard to observe birds from the comfort of your sofa!
All this was completed just in time as, on leaving the Museum, one lucky staff member glanced upwards to see the first swift of the season glide across the sky above the tower. Perhaps a visitor travelling further north to breed, just passing through, or perhaps an early arrival feeding up and replenishing itself before starting its nesting, checking its old nest site is still there and reminding us, as Ted Hughes continued in his poem, that…
They’ve made it again,
Which means the globe’s still working, the Creation’s
This week is Swift Awareness Week and that means it’s time to celebrate our screaming summer visitors – the avian ones, that is.
Here at the Museum we eagerly await the return of these long distance migrants each May. This is not only because for many of us they herald the start of summer, but also because the swifts that nest each year in the Museum tower are part of the longest-running continuous study of any bird species in the world.
Taking the long view of these amazing birds we know that, like all birds, they evolved from a particular group of dinosaurs. Birds, in effect, are living dinosaurs. The earliest fossil swift, the ‘Scania Swift’, is around 49 million years old and shows us that by this time they had already evolved in forms that are virtually indistinguishable from today’s birds. Today, they have diversified into around 100 different species including our Common Swift (Apus apus).
Swifts have taken life on the wing to the extreme. Not only are they the fastest recorded bird in level powered flight, reaching speeds of nearly 70mph, but once launching themselves from the nest that they hatched in they may not land for the next two years of their lives!
They are so adapted to life in the air that they are capable of eating, mating and even sleeping on the wing. During sleep, it is thought that the two hemispheres of the brain take it in turns to nap as the swift slowly circles at heights of up to 30,000 feet. They do not even land to collect nesting material, instead relying on whatever feathers or pieces of plant material are floating in the air to build their nests.
During this two-year flight they will follow their food – the seasonal blooms of flying insects that appear after summer rains – on a 14,000 mile annual migration to southern Africa and back, living in perpetual summer.
Whilst for a long time scientists thought swifts were closely related to similar looking birds, swallows and martins, DNA analysis has revealed that they are the product of another amazing type of evolution – called convergent evolution – where organisms with similar lifestyles independently evolve similar traits. It turns out that whilst swifts may look like swallows, they are actually more closely related to hummingbirds; swallows, on the other hand, are more closely related to kingfishers than to swifts.
Studies show that the population of breeding swifts in the UK has roughly halved between 1995 and 2016. The causes of this decline are debated: Lack of nest sites, lack of food, and changes to global weather patterns have all been implicated. The truth is that a bird which lands only once a year is extremely difficult to study.
We hope for a successful breeding season here in the tower, but if you would like to observe them yourself you can watch the swifts on our nest cam and compare the ups and downs of their populations over the years on our website.