Swifts flying around the Museum tower

Flight and fight

By Chris Jarvis, Education Officer

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.

The body of a dead swift found during the weekly survey of the colony of birds in the Museum tower

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.

Swifts flying around the Museum tower
Swifts circle the tower prospecting for potential nest sites, screaming and banging to check which are occupied and which are vacant. Image: Gordon Bowdery

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.

Cover of 2018 edition of Swifts in a Tower by David Lack
Cover of the 2018 edition of Swifts in a Tower by David Lack

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.

Meanwhile keep an eye on our nest box; you never know what drama may play out next…

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.

Eggs in the tower

By Chris Jarvis, Education Officer

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 swifts circle the Museum tower looking for suitable nesting sites

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

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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.

Chris Jarvis cleaning the nest box in the Museum Tower Room

A swift return

Chris Jarvis cleaning the nest box in the Museum Tower Room

by Chris Jarvis, Education Officer

‘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.

Video courtesy Oxford Swift City

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.

Chris cleaning the swifts’ nest boxes with a feather duster

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 80 nest boxes has to be carefully cleaned before the swifts return from Africa

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

Still waking refreshed, our summer’s

Still all to come —

Excavating amber

First amber excavation in the El Soplao outcrop, Cantabria, N Spain in 2008. Credit IGME-UB.

By Dr Ricardo Perez-De-La Fuente, Research Fellow

Amber, or fossilised plant resin, is a unique material to learn about the history of life on Earth. Its incredible preservation and ability to capture life “in action” are well known thanks to the Jurassic Park saga, but fewer people know where amber is found, what it looks like in the field, and how it is gathered.

Cretaceous amber, about 130 to 70 million years old, is the oldest amber that provides abundant fossils, specifically insects and spiders. Ecosystems drastically changed during this period due to global greenhouse conditions and the diversification of flowering plants, among other factors. Amber from that time has been discovered in Lebanon, Spain, France, Myanmar, eastern United States, Canada, and northern Russia.

My research team and I carry out regular amber excavations in northern Spain, working in teams of six to ten people. The outcrops that we excavate are often located next to roads and highways because amber is typically uncovered during roadworks. Excavations take place during the summer or fall to try and minimise the risk of rain, and we usually embark on one field trip each year.

The goal is to recover as much amber as possible – usually a few kilograms – from the muddy and sandy sediments. These materials were transported downstream tens of million of years ago by heavy rain and river swellings from the forests where the resin was produced, before being finally deposited in near-shore areas.

Manual extraction of amber. Credit IGME-UB
Manual extraction of amber in the El Soplao outcrop, Cantabria, northern Spain in 2008. Credit: IGME/UB.

I find amber excavations quite romantic. In the field, amber has a dull appearance that makes it difficult to distinguish from rocks or woody remains. This is due to an opaque crust resulting from oxidation in the sediments and other processes.

This outer layer makes detecting potential fossils inside the amber highly unlikely while the excavation is ongoing. So, in the field we just gather as many amber pieces as possible, and hope for the best.

Only when amber is polished – or shows broken surfaces – does its distinct yellowish to reddish shine emerge, and any possible fossils within become evident. Some ambers are highly fossiliferous, while others are very poor in fossils.

Amber can be gathered by hand using regular tools such as hammers. However, the most efficient method to extract amber from soft sediments is with concrete mixers! This rather unsophisticated piece of equipment provides the best way to recover medium quantities of amber in the field.

We charge water and amber-bearing sediments into the mixer, and after stirring for a while amber floats to the top because it is less dense than muddy water. Then, the surface of the water containing the amber is poured into sieves, which separates even the tiniest pieces.

Amber pieces recovered in a sieve after washing
Amber pieces recovered in a sieve after having been “washed” from their sediment. First amber excavation in the La Manjoya outcrop, Asturias, northern Spain in 2017.

After fieldwork, many hours will be spent looking for fossils within the amber and preparing them. Gathering raw amber is just the first part of a process in unearthing the secrets held within – fragments of encapsulated time.

Top image: First amber excavation in the El Soplao outcrop, Cantabria, N Spain in 2008. Credit: IGME/UB.

Uncovering ancient threads

By Dr. Frankie Dunn, Research Fellow

Some of the very oldest complex, macroscopic communities on Earth appear in the fossil record about 570 million years ago and record the presence of a group of organisms – the rangeomorphs – with an unfamiliar body plan that, at their ultimate extinction, was lost from life’s repertoire.

Rangeomorphs are characterised by a strange frondose branching anatomy, where large primary branches host smaller branches which themselves host smaller branches again. This arrangement appears to maximise the surface-area to volume ratio of the organism, rather like a lung or a gill would today.

The smallest known rangeomorphs are less than a centimetre in length, but they grew huge and the largest records indicate they could stand more than two metres tall. There is no evidence to suggest that rangeomorphs were able to move around, rather, they lived stuck to the sea floor in the deep ocean, far below the reach of light.

Despite this strange set of characters, there is growing consensus that rangeomorphs likely represent very ancient records of animal life. However, they lived at such a remote time in Earth’s history that they do not possess any direct living descendants. Given all this, it may not be a surprise to hear that we know relatively little about how these organisms made their living and came to dominate the ancient seafloors.

Fig A
The UNESCO world heritage site Mistaken Point in Newfoundland, Canada, is one of the sites on which we find exceptionally preserved rangeomorph fossils. Photo: Alex Liu.

In order to better understand them, my co-author Alex Liu and I travelled to Newfoundland, Canada to explore the rocks which host these remarkable fossils and over the past few years we have made an unexpected discovery. We found that fine filamentous threads connect rangeomorph fronds of the same species, in some cases over many meters, though they are typically between two and 40 centimetres long.

N3
An undescribed rangeomorph fossil with filamentous connections at the base of the frond. We find that this species of rangeomorph can be connected to each other over meters! Photo: Alex Liu. 

It is possible that these filaments were involved in clonal reproduction, like strawberry plants today, but they may have had additional functions such as sharing nutrients or providing stability in strong ocean currents.

The discovery of the filaments means that we have to reconsider how we define an individual rangeomorph, and may help us understand how rangeomorphs (seemingly) rapidly colonised deep-sea environments. Either way, some reassessment of the palaeobiology of these unique organisms is certainly required!

More information:

  • Read the full research paper here.

 

Top image: Beothukis plumosa, a rangeomorph from Newfoundland showing the intricate branching anatomy of rangeomorphs. Photo: Alex Liu.

Diving into deep time

Our current First Animals exhibition is extending its run until 1 September, and to mark the extension our Research Fellow Imran Rahman takes a look at how animal life in the ancient oceans was brought to life in our Cambrian Diver interactive installation.

One of the biggest challenges in developing the First Animals exhibition lay in visualising rare fossil specimens as ‘living’ organisms, transforming them from two-dimensional imprints in the rock into three-dimensional animated computer models.

Many of the specimens on display in First Animals were collected from sites of exceptionally well-preserved fossils called Lagerstätten. These deposits preserve the remains of soft-bodied organisms that are almost never seen in the fossil record; things such as comb jellies and worms, as well as soft tissues such as eyes, gills and muscles. Even so, most of these fossils are flattened and two-dimensional, which makes it very difficult to reconstruct what they looked like in life.

Vetulicola cuneata from the Chengjiang fossil site had a large body with triangular openings on either side and a segmented tail. Its three-dimensional shape is uncertain.

To help exhibition visitors visualise the animals in a living environment we worked closely with Martin Lisec and his team at Mighty Fossils to create a set of detailed computer models of a key set of animals. We have worked with Martin before on the video of a Jurassic sea inhabited by plesiosaurs and other marine animals for our Out of the Deep display. That was very successful, but our idea for First Animals was even more ambitious: to create a unique interactive installation called the Cambrian Diver.

The material focused on the Chengjiang animals from the Cambrian of Yunnan province, China, which provides the most complete record of an early Cambrian marine community, from approximately 518 million years ago. Using fossil evidence of the organisms thought to have lived at the time we selected 12 species that were representative of the diversity of the Chengjiang biota.

The first phase was collecting as many materials as possible to be able to create 3D models. As usual, we started with rough models, where we set basic dimensions, shapes and proportions of body parts. Once approved, we moved to very detailed models for the animations, artworks and textures for less detailed models to be used within the interactive application. – Martin Lisec, Mighty Fossils

Images showing a preliminary 3-D model of the lobopodian Onychodictyon ferox in multiple views, with annotations in yellow highlighting changes suggested by Museum researchers.

To provide two-dimensional templates for Mighty Fossils to work from we scoured the scientific literature for the most recent accurate reconstructions available for each of the species.

The predatory arthropod Amplectobelua symbrachiata is a good example. We drew heavily upon a 2017 paper by Dr Peiyun Cong and colleagues, which included a very detailed reconstruction of the head region. This reconstruction shows that the underside of the head of Amplectobelua consisted of a rod-shaped plate, a mouth made up of two rows of plates, and three pairs of flaps with spiny appendages, all details that are included in our 3D model.

Scientific reconstruction (left) and our 3D model (right) of the arthropod Amplectobelua symbrachiata. Left-hand image modified from Cong et al. (2017).

Colour and texture were another consideration. To inform these we looked at living species that are thought to have similar modes of life today. For Amplectobelua, a free-swimming predator, we examined the colouration of modern marine predators such as sharks. Many sharks have countershading, with a darker upper side of the body and a lighter underside, which acts as camouflage, hiding them from potential prey.

We reconstructed our Amplectobelua model with similar countershading camouflage, with blue and red colouration inspired by the peacock mantis shrimp, a brightly coloured predatory arthropod that lives in the Indian and Pacific oceans.

3-D model of Amplectobelua in angled upper (top) and lower (bottom) views, showing countershading.

The next vital step was establishing how the animals moved and interacted with one another. This is a major challenge because in many cases there are no modern equivalents for these extinct early animals. For Amplectobelua we inferred that the flaps on the sides of the body were used for swimming, with the tail fan helping to stabilize the animal as it moved through the water. This agrees with previous interpretations of swimming in closely related animals such as Anomalocaris.

The models were built and textured by Mighty Fossils using the 3D gaming engine Unity. The video below is an accelerated sequence showing how the elements of the model are layered together.

The finished, animated and annotated Amplectobelua model is shown below, and can be zoomed and rotated. All the models generated by Mighty Fossils for the First Animals exhibition are gathered in a collection on our Sketchfab page.

Once animated models of all 12 species were created we placed them in a realistic marine environment. Study of the rocks preserving the Chengjiang fossils suggests these animals lived in a relatively shallow, well-lit sea, perhaps 50 metres deep and characterised by a flat, muddy seafloor. A continuous shower of organic particles is thought to have filled the water column, as in modern oceans.

Reconstruction of the Cambrian seafloor with ‘marine snow’

Based on present-day marine ecosystems, we infer that the number of immobile suspension feeders would have been much greater than the number of predators. As a result, we included multiple individuals of the suspension feeders Cotyledion, Saetaspongia and Xianguangia, which were tightly grouped together, but only a small number of the active predators Amplectobelua and Onychodictyon.

This scene is now populated with animals, including two predators: Amplectobelua (swimming) and Onychodictyon (centre)

The final step involved setting up a camera and user interface to allow visitors to discover the various animals in our interactive environment. For this we worked with creative digital consultancy Fish in a Bottle to identify eight locations, each focused on a different animal.

As the video above shows, users can navigate between locations by touching an icon on the screen, and when the Cambrian Diver sub arrives at a location information about the animal, its mode of life and its closest living relatives is presented on-screen. A physical joystick allows users a 360-degree rotation to look around the scene, and explore the ancient watery world.

This project was significantly bigger than the Out of the Deep work we had done previously with the Museum, mainly because of the complicated approval procedure needed for 20 individual 3D models. Along with three large illustrations, two animations and the interactive application this was a big workload! Fortunately, we managed to finish the whole project on time for the opening of the exhibition. – Martin Lisec