It Wouldn’t be Easter without Eggs – Tim Birkhead explains the Science behind a Bird’s Egg

Tim Birkhead, The Most Perfect Thing: Inside (and Outside) a Bird’s Egg

When I started to write about birds’ eggs I wondered whether anyone had established which of the different shapes was most common. Obviously when we talk about something being egg shaped we are usually thinking of a hen’s egg, which is ‘oval’, but with an obvious blunt and pointed end and whose greatest width lies closer to the blunt end. To my surprise nobody seems to have quantified egg shape across all families of birds. Part of the difficulty, of course, is coming up with a simple index of shape. Researchers have devised several complicated ways of describing egg designs but there is no single number that captures the full range of shapes. For this reason most books dealing with egg shape simply show – as I do here – a set of outlines or silhouettes illustrating the different types that exist.

One thing we do know is that as well as being characteristic for a particular species, shape is also fairly characteristic for particular families of birds, too. Owls, for example, typically lay spherical eggs;

egg image1

Different shapes of birds’ eggs. From left to right: Ross’s turaco (spherical), ruff (pyriform), hummingbird (oblong oval or elliptical), crowned sandgrouse (oblong oval or elliptical), African thrush (oval), Slavonian grebe (bi-conical or long subelliptical), alpine swift (ellipitical ovate or long oval). Redrawn from Thomson, 1964.

waders (shorebirds) lay pyriform eggs; sandgrouse produce oval or elliptical eggs; and grebes produce biconical eggs.  As a biologist, two questions come to mind. How are eggs of different shapes made, and why are they the shape they are? The first question is about the mechanics of making an egg; the second concerns the adaptive significance of different egg shapes.

egg image2
Thinking about how a female bird produces eggs of a particular shape, my natural inclination was to imagine that the shape was determined by the shell: shape and shell created together. The truth is more bizarre. The contours of a bird’s egg are governed by its membranes, the parchment-like layer inside the shell – as my eggin- vinegar experiment suggested – rather than by the shell itself. Once you know that the membrane determines the shape it isn’t too difficult to imagine the process.

In an ingenious X-ray study of egg formation conducted in the late 1940s, John Bradfield could see that the shape of the hen’s egg was determined before the shell had even started to form, prior to entering the shell gland. Instead, he could see that the egg’s shape was established in the isthmus, the region of the oviduct immediately anterior to the shell gland, where the shell membrane around the egg is created. He noticed, too, that the part of the isthmus adjacent to the shell gland is ‘more contractile and more like a sphincter’ than the other end adjacent to the magnum, suggesting that: ‘Since the egg greatly distends the narrow isthmus [region of the oviduct], it is to be expected that the caudal [tail] end of the egg, situated in the more contractile part of the isthmus, will become more pointed than the cranial [head] end.’ He adds, however, that this suggestion is far from proved ‘and the problem remains without a clear-cut solution.

At the end of the egg-shape spectrum opposite to the guillemot are certain owls, tinamous and bustards that lay almost spherical eggs. How is that done? Does the isthmus in these birds lack the sphincter that Bradfield saw in the hen? Or does the egg turn continuously as the membrane is laid down so that the sphincter applies a uniform pressure all over the egg? We don’t know.

In humans the maximum size of a baby at birth is determined by the size of the ‘birth canal – that is, the internal diameter of the pelvic girdle. Our present ability to perform caesarian operations removes this constraint, but prior to the twentieth century and the routine use of caesarian section, babies who were too big – or whose heads were too big – failed to be delivered successfully, got stuck and died, usually along with the mother. Strong selection indeed. Because the bones that form the human cranium are still not fused at birth there is some flexibility (literally), permitting the skull to adopt a different shape during birth and allowing some relatively big-headed babies to be born.

Read more in Tim Birkhead’s The Most Perfect Thing: Inside (and Outside) a Bird’s Egg

9781408851258

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It Wouldn’t be Easter without Eggs – Tim Birkhead explains the Science behind a Bird’s Egg

Tim Birkehad, The Most Perfect Thing: Inside (and Outside) a Bird’s Egg

When I started to write about birds’ eggs I wondered whether anyone had established which of the different shapes was most common. Obviously when we talk about something being egg shaped we are usually thinking of a hen’s egg, which is ‘oval’, but with an obvious blunt and pointed end and whose greatest width lies closer to the blunt end. To my surprise nobody seems to have quantified egg shape across all families of birds. Part of the difficulty, of course, is coming up with a simple index of shape. Researchers have devised several complicated ways of describing egg designs but there is no single number that captures the full range of shapes. For this reason most books dealing with egg shape simply show – as I do here – a set of outlines or silhouettes illustrating the different types that exist.

One thing we do know is that as well as being characteristic for a particular species, shape is also fairly characteristic for particular families of birds, too. Owls, for example, typically lay spherical eggs;

egg image1

Different shapes of birds’ eggs. From left to right: Ross’s turaco (spherical), ruff (pyriform), hummingbird (oblong oval or elliptical), crowned sandgrouse (oblong oval or elliptical), African thrush (oval), Slavonian grebe (bi-conical or long subelliptical), alpine swift (ellipitical ovate or long oval). Redrawn from Thomson, 1964.

waders (shorebirds) lay pyriform eggs; sandgrouse produce oval or elliptical eggs; and grebes produce biconical eggs.  As a biologist, two questions come to mind. How are eggs of different shapes made, and why are they the shape they are? The first question is about the mechanics of making an egg; the second concerns the adaptive significance of different egg shapes.

egg image2
Thinking about how a female bird produces eggs of a particular shape, my natural inclination was to imagine that the shape was determined by the shell: shape and shell created together. The truth is more bizarre. The contours of a bird’s egg are governed by its membranes, the parchment-like layer inside the shell – as my eggin- vinegar experiment suggested – rather than by the shell itself. Once you know that the membrane determines the shape it isn’t too difficult to imagine the process.

In an ingenious X-ray study of egg formation conducted in the late 1940s, John Bradfield could see that the shape of the hen’s egg was determined before the shell had even started to form, prior to entering the shell gland. Instead, he could see that the egg’s shape was established in the isthmus, the region of the oviduct immediately anterior to the shell gland, where the shell membrane around the egg is created. He noticed, too, that the part of the isthmus adjacent to the shell gland is ‘more contractile and more like a sphincter’ than the other end adjacent to the magnum, suggesting that: ‘Since the egg greatly distends the narrow isthmus [region of the oviduct], it is to be expected that the caudal [tail] end of the egg, situated in the more contractile part of the isthmus, will become more pointed than the cranial [head] end.’ He adds, however, that this suggestion is far from proved ‘and the problem remains without a clear-cut solution.

At the end of the egg-shape spectrum opposite to the guillemot are certain owls, tinamous and bustards that lay almost spherical eggs. How is that done? Does the isthmus in these birds lack the sphincter that Bradfield saw in the hen? Or does the egg turn continuously as the membrane is laid down so that the sphincter applies a uniform pressure all over the egg? We don’t know.

In humans the maximum size of a baby at birth is determined by the size of the ‘birth canal – that is, the internal diameter of the pelvic girdle. Our present ability to perform caesarian operations removes this constraint, but prior to the twentieth century and the routine use of caesarian section, babies who were too big – or whose heads were too big – failed to be delivered successfully, got stuck and died, usually along with the mother. Strong selection indeed. Because the bones that form the human cranium are still not fused at birth there is some flexibility (literally), permitting the skull to adopt a different shape during birth and allowing some relatively big-headed babies to be born.

Read more in Tim Birkehad’s The Most Perfect Thing: Inside (and Outside) a Bird’s Egg

9781408851258

How to get Creative with Herrings

This month, we’re celebrating one of nature’s real unsugn heroes – the Herring.

Scots like to smoke or salt them. The Dutch love them raw. Swedes look on with relish as they open bulging, foul-smelling cans to find them curdling within. Jamaicans prefer them with a dash of chilli pepper. Germans and the English enjoy their taste best when accompanied by pickle’s bite and brine.

Throughout the long centuries men have fished around their coastlines and beyond, the herring has done much to shape both human taste and history. Men have co-operated and come into conflict over its shoals, setting out in boats to catch them, straying, too, from their home ports to bring full nets to shore. Women have also often been at the centre of the industry, gutting and salting the catch when the annual harvest had taken place, knitting, too, the garments fishermen wore to protect them from the ocean’s chill.

In his book, Herring Tales,  Donald S. Murray has stitched together tales of the fish that was of central importance to the lives of our ancestors, noting how both it – and those involved in their capture – were celebrated in the art, literature, craft, music and folklore of life in northern Europe.

Donald contemplates the possibility of restoring the silver darlings of legend to these shores. And to help spark some imagination, he provides some engenious examples of how we can make them live on via the box they arrive in!

A Wheel Barrow

wheel barrow

A Go-Cart

cart

A Baby Cot

cot

A Bike Carrier

Dog Carrier

A Milk Box

milk box

Celebrate the Herring this month with Herring Tales – and join Donald on his campaign to restore this versatile little creature back to former glory!

9781472912169

British Wildlife Blog has a New Home!

We are delighted to announce our new partnership with Bloomsbury Publishing – the UK’s number one publisher of Natural History. Both Bloomsbury and British Wildlife would like to invite you to join our new community hub at the Bloomsbury Wildlife Blog. Stay up to date with the latest Natural History news from our authors and editors here.

You can also join in the conversation on the Bloomsbury Wildlife Twitter feed at @chiffchat. Please do follow us for updates from British Wildlife and Bloomsbury.

British Wildlife Publishing & Bloomsbury – An Announcement

Hello,

A very happy new year to you all. Before returning to normal service with posts about all aspects of British natural history and wildlife, we have a brief announcement to make about the ownership of British Wildlife Publishing.

This is that the company has been acquired, as part of Osprey Publishing, by the very illustrious Bloomsbury Publishing. We can’t tell you very much more than that currently, as all manner of details are still being worked out, but since Bloomsbury is well known for its very estimable natural history publishing you should be confident that we – and the books and magazines – are in safe, knowledgeable and above all careful hands.

Other than that, all that remains is to say please continue to watch this space for more posts about what we’re all REALLY interested in: the wildlife of these beautiful islands.

All the very best for 2015,

British Wildlife Publishing

Dr Nigel Holmes 1949 – 2014

Many of you will already know that Nigel Holmes passed away last month. Nigel was an indispensable pillar of river conservation and restoration, a vital mentor and valued friend to many, a renowned author, and a devoted husband and father. He is sorely missed by all who knew him.

We share with you a lovely picture of Nigel taken by his colleague and friend Dr Paul Raven (with whom he co-authored Rivers), and Peter Marren’s full obituary, which can be read in The Independent at the link below.

60 Poland 2007ii

http://www.independent.co.uk/news/people/news/doctor-nigel-holmes-ecologist-who-led-efforts-to-restore-degraded-rivers-and-formulated-a-scientific-classification-used-across-europe-9836624.html

25 Years of Conservation in Britain – Peter Marren, August 2014

What makes Britain punch above its weight in biodiversity terms is not superior protection but geography …’ 

Last week, we featured on this blog Simon Barnes’ look at the next 25 years of British conservation. This week we offer another extract from the magazine, this time from Peter Marren’s August piece on the last 25 years.

Perhaps the greatest contrast between 1989 and today, however, is to be found not in the state of nature but in human perception. We are better informed about our world than we were then. Children learn all about environmental responsibility at school, even if they do not learn much about nature. Today everyone knows about climate change whether or not they choose to believe it (the wildlife believes it; that is why our more mobile species are moving farther north year by year). Many people have acquired an environmental conscience. They recycle glass and plastic, and insulate the house, and perhaps buy organic produce and fair-trade goods. They see trees as planet-saving, and they support windfarms and fuss about carbon footprints and air miles. ‘Green’ policies now permeate society and are upheld to different degrees by all political parties. One of the benefits of this new-found earth-consciousness is that farmers and landowners are willing to be a little kinder to the land; they plant hedges and preserve copses, and some try to reduce their dependency on poisons and chemicals. Local authorities routinely plant wild flowers on verges and in other public spaces. Every little helps.

One of the outcomes of the ‘big green swing’ has been the growth in membership of wildlife bodies, aided by successful television series such as Springwatch. Since 1989 the RSPB has doubled its membership to over a million, a measure of just how popular birdwatching has become. The county wildlife trusts, too, have a healthy membership of around 800,000. Even a relatively small charity such as Butterfly Conservation now has about 400 members for every native species of butterfly. The trusts have also got richer, not only through increased membership but also from Heritage Lottery grants and other windfalls such as tax credits and legacies. They can afford to do more than they used to. As a career opportunity, nature offers much more today than it did in 1989, whether in broadcasting and filming, wildlife holidays, consultancies and charities or in one of the government agencies.

State institutions with some responsibility for the natural environment have also grown in power and influence. The Environment Agency came into being in 1995, charged with keeping our beaches and rivers clean and healthy and reducing floods. The Broads, the New Forest and the South Downs have been designated as National Parks, along with, in Scotland, Loch Lomond and the Cairngorms. What, in 1989, was still the Nature Conservancy Council became three country agencies that by degrees took on other roles – land access and then farm income support – with a budget to match. They may lack political influence, but at least they have enough resources to operate the various official schemes to help wildlife – stewardship agreements, voluntary agreements on SSSIs and so on.

Perhaps the most interesting new idea since 1989 is that of rewilding. It began, in effect, with the highly successful reintroduction of the Red Kite into England and Scotland, followed by releases of White-tailed Eagles Haliaeetus albicilla, Great Bustards Otis tarda and Eurasian Cranes Grus grus into parts of their former range. In Scotland, the Eurasian Beaver Castor fiber has been semi-released on a trial basis; other animals have escaped from captivity and are surviving on the run. A few places have experimented with semi-wild beasts such as Konik ponies and water buffalo Bubalus as (in the jargon) ‘management tools’. There have also been attempts to create larger areas out of isolated habitats, most notably the Great Fen Project, in East Anglia, by restoring intervening land to wetland and wood. In Scotland, especially, there have been attempts to restore open hillsides with forest. All this has come together into a developing philosophy of ‘rewilding’ barren landscapes, partly for conservation reasons but also to satisfy a vaguely felt desire for wilder places with wild animals to match. It could even pave the way for the restoration of long-lost big beasts: Eurasian Lynx Lynx lynx, Eurasian Elk Alces alces, European Bison Bison bonasus, even Wolves Canis lupus. It may happen, but it probably won’t.

Nature conservation in a densely populated, intensively farmed island like Britain is never going to be easy. With 383 people per square kilometre, England has three times the EU average population density. Moreover, there are, mainly through immigration, two million more of us than there were in 1989. The Continental model of creating National Parks in wild and remote places does not work here, mainly because England, at least, has so few such places. Our National Parks are normal countryside that just happens to be prettier than the places outside. There are planning constraints, slightly better resources and perhaps more rights of way, but that is about all. With the possible exceptions of the Broads and the New Forest, our Parks do not add significantly to the conservation of wildlife. Our British alternative, the SSSI, is a collection of often small, isolated ‘islands’ amid lifeless crops and suburban sprawl. What makes Britain punch above its weight in biodiversity terms is not superior protection but geography: our long coastline and our complex rocks, ranging from pre-Cambrian to post-glacial gravel, produce some of the most variable small-scale scenery in Europe. But we are also a cool, wet, everlastingly green island. Mosses and lichens do well in our damp Atlantic climate. In every other major terrestrial group except birds, however, we are impoverished compared with our nearest Continental neighbours.

Successful conservation is all the more difficult because there are pervasive things which we are unable to do much about. One of them is increased soil fertility, especially along roadsides and watercourses. A big increase in nitrogen from fertiliser and traffic emissions has shifted the balance of plant competition in favour of bulky, shading, fast-growing species such as Cow Parsley Anthriscus sylvestris, Hogweed Heracleum sphondylium, nettles and coarse grasses. Their spread comes at the expense of smaller plants that are thereby deprived of heat and light, as well as space. Increased fertility is probably linked to the increase in scrub in natural grassland and heaths and the spread of Tor-grass Brachypodium pinnatum on downland. Its most noticeable effect is fewer flowers (and hence less colour), less diversity and all that that implies for dependent invertebrates and food-webs. The failure to do anything about such observable changes in the soil is one of the more significant failures of conservation.

To the increased competition between native species must be added competition from introduced species. The globalisation of trade has vastly increased the number of ‘escaped’ plants, animals and invertebrates – you have only to look at the size of recent county floras to appreciate the scale of it. In some ways this is an exciting development, increasing the dynamic of nature and introducing a host of colourful and, mostly, harmless species to the urban landscape. The downside, however, is that a few of them become too successful, compete with native species and sometimes outcompete them. Everyone knows about the impact of American Mink Neovison vison, Grey Squirrel Sciurus carolinensis and Ruddy Duck Oxyura jamaicensis on native animals. More fundamental damage may be caused by humbler creatures such as the Harlequin Ladybird Harmonia axyridis or accidentally imported flatworms from far-away New Zealand. Aquatic habitats are particularly vulnerable to species we could well do without, such as Signal Crayfish Pacifastacus leniusculus, various ‘killer shrimps’ and garden-pond throw-outs such as the pernicious New Zealand Pigmyweed Crassula helmsii. Most serious of all, we are introducing diseases that attack trees. Ash dieback is only the latest in a catalogue of new pathogens whose arrival and spread we seem powerless to prevent.

Then there is the weather. Climate change was a recent concern back in 1989. It is now, of course, at the forefront of the political agenda worldwide. In Britain every year seems to throw up new records, and the recent trend is for milder, wetter, less predictable seasons. If such places as the Somerset Levels continue to flood for months on end, farming there will become impossible. The gainer, potentially, will be nature. The same would be true if river catchments were afforested, or at least if they were afforested in the right way. But for now such gains are theoretical. Shifting seasons and bad summers create instability that throws the natural systems of the world into chaos. Climate change as we have experienced it in Britain so far is, on balance, not good for wildlife.

This is an excerpt; the full, much longer version of this article was published in August’s edition of British Wildlife magazine. Subscribe or order back-issues here: www.britishwildlife.com

Order Peter Marren’s book Mushrooms (British Wildlife Collection 1) here.

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'The most important and informative publication on wildlife of our times' – The Independent. This blog is a member of The UK & Ireland Natural History Bloggers group: www.uknhb.blogspot.com