Author: More than a Dodo

Swifts flying around the Museum tower

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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.

Robin

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The dawn chorus

By Chris Jarvis, Education Officer

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.

Robin
The Robin (Erithacus rubecula), Britain’s national bird, is one of the many voices contributing to the dawn chorus. Image: Scott Billings

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.

A verdant scene at Harcourt Arboretum

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…

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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.

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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.

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Through the looking glass

With our Life, As We Know It redisplay project now underway, our Senior Archives and Library Assistant Danielle Czerkaszyn takes a behind-the-scenes look at how we captured the contents of the current displays for the Museum’s archive.

The archive here holds a unique collection of natural history books, journals and documents covering a wide range of subjects related to the Museum’s collections and research. It also contains papers and objects on the history of the building, providing an institutional memory of Oxford’s ‘University Museum’ since its foundation in 1860.

From an archive perspective it was really important to document the current layout of the cases, their specimens and text before they were removed from the court to make way for the new showcases in the first phase of our redisplay work.

The museum in late 2019

The displays as we know them – with exhibitions on the Oxfordshire dinosaurs, Alice in Wonderland, the Oxford Dodo, and more – were last changed in 2000. For the last 20 years visitors to the Museum would remember their first time being wowed by the Megalosaurus jaw – the world’s first scientifically-described dinosaur – or charmed by the Dodo made famous in Lewis Carroll’s Alice Adventures in Wonderland.

Although after 20 years it is time for a change, the stories and information in the displays are too good to be forgotten. So before anything was removed we began to build the archive for the future.

A display of the fossilised remains of Megalosaurus
The previous display on Megalosaurus: The First Dinosaur

The best way to capture all the information of the displays was through high resolution photography, but this was not as straightforward as we hoped.

The first two obstacles to good photographs are pretty obvious to anyone looking at the cases: glass causes huge amounts of glare; and each case has a big dividing line down the centre where the two sliding glass doors meet, cutting what should be a lovely seamless image into two halves.

To avoid glare and the solve the problem of the dividing line, our photographer Scott opened each individual side of the case, photographed two or three images of the display, and then stitched the separate photos together using Photoshop.

Each case was photographed in two or three segments
The segments were then stitched back together and adjusted for exposure and colour balance to create the final image

Another obstacle to taking good photographs of the displays came from the Museum itself. Some of our larger display furniture, such as the glass case for the Atlantic Bluefin Tuna or the huge T. rex plinth – got in the way of a nice straight shot. Because these items are so large and heavy they were impossible to move, so we had to improvise and do our best.

Capturing the displays before the current cases were removed allowed us to keep an archival record of their contents

Thankfully, we managed to get shots of all 24 displays before they were removed and so a record of each case now rests with the Museum’s archive. If anyone wants to know what the display cases in the court looked like from 2000 to 2020, they will now be able to look back at the images in the archive and recall the magic of the Oxford Dodo exhibit that perhaps first made them fall in love with the Museum.

Our new displays are now in development, and will include some beautiful presentations of the diversity of life, looking at the importance and fragility of biodiversity and human impact on the environment. These new exhibits will show how the biological processes of evolution combine with the geological processes of our dynamic Earth to give rise to the immense, interconnected variety of the natural world.

We look forward to telling you more about that here as the project progresses.

The Life, As We Know It redisplay project is supported by a generous grant from FCC Communities Foundation.

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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.