Understanding Eggs: How mechanical engineering helped a leading zoologist to crack an egg shaped question.

Research from a leading zoologist at the Department of Animal and Plant Sciences that also involved input from Mechanical Engineering academics was featured in a nature documentary with Sir David Attenborough.

Professor Tim Birkhead with Sir David Attenborough with a selection of eggsProfessor Tim Birkhead, a Fellow of the Royal Society and lecturer of Behavioural Ecology at the University of Sheffield, appeared on the ninth episode of the BBC’s Natural World series. The documentary explored how eggs are made, why they are the shape they are and why eggs are used in reproduction despite millions of years of evolution.

Drawing on research from Professor Birkhead’s book ‘The Most Perfect Thing: Inside (and Outside) a Bird's Egg’, the programme followed the story of how the egg is made and fertilised, as well as how the chick develops and hatches.

And input from University of Sheffield mechanical engineers, Professor Patrick Fairclough and Professor Roger Lewis, also supported Professor Birkhead’s research into why eggs are the shape they are – and in particular for cliff dwelling species such as the guillemot.

“A bird's egg is an external, free-standing incubation system’” explains Professor Birkhead. “It works for birds breeding at the poles and on the equator; for birds incubating on wet, soggy nests and birds breeding in arid deserts and at different altitudes.

“The guillemot egg shape has, for years, been recognised as the most extreme. It’s more pointed than any other species and that’s been a puzzle for a long time.”

The 3D printed eggs that were used as part of the researchWhilst investigating its pyriform (pointed) shape, Professor Birkhead approached Professors Fairclough and Lewis to undertake research exploring the way the egg rolled and whether this motion was a key factor in the shape evolution.

“We were delighted to collaborate with Professor Birkhead and colleagues from Animal and Plant Sciences to better understand why guillemot eggs are the shape they are,” explains Professor Lewis, who alongside Professor Fairclough are acknowledged in The Most Perfect Thing book.

“Our part in the puzzle involved designing a ramp that allowed us to experiment with different egg shapes and how they rolled. We used a high speed camera and image analysis to look at the relationship between egg shape and motion, exploring whether the shape evolved to avoid eggs falling from the narrow ledges they’re laid on.

“The eggs we used were additively manufactured by the Centre for Advanced Additive Manufacturing (AdAM) at the University of Sheffield too, so it was a really interesting collaboration across the departments.”

However, through his research, Professor Birkhead discovered that traditional explanations for the pointed shape – such as to avoid falling - are incorrect. Instead he suggests that the pointed shape helps keep the large end of the egg, where the chick's head lies, free from dirt on the often filthy ledges where guillemots breed.

Professor Birkhead said his experience of working with Sir David was extraordinary.

“It was a real privilege to work with him. He was charming, knowledgeable and above all, modest. The fact that in an earlier interview (in BBC-Wildlife) he referred to my book The Most Perfect Thing — on which the programme is based — as 'magnificent' is the greatest praise a zoologist could ever hope for.”

You can read more about the programme and Professor Birkhead’s involvement at www.sheffield.ac.uk/news