John M. Marzluff extols a rich history of ornithology's debt to egg collecting.

The Most Perfect Thing: Inside (and Outside) a Bird's Egg Tim Birkhead Bloomsbury: 2016. 9781408851258 | ISBN: 978-1-4088-5125-8

Tim Birkhead has spent much of the past four decades watching birds, and in particular mucking around guano-covered ledges on which seabirds breed. His insights have revolutionized ornithologists' understanding of mate fidelity; his ability to distil complex science for the general reader, for example in Bird Sense (Bloomsbury, 2013), has revealed what it is like to be a bird. Now, with an eye on past discoveries and persistent puzzles, The Most Perfect Thing reveals what it is like to become a bird — from nascent ovum to shelled egg and beyond. Some birds evolve signature egg colours and patterns to confuse nest parasites such as the cuckoo finch. Each column shows eggs from one host species. Credit: Eleanor Caves and Claire Spottiswoode

Birkhead starts his story in the nineteenth century, on English cliffs where eccentric collectors wait anxiously for daring “climmers” to fetch unusually shaped and patterned eggs from the nests of common guillemots (Uria aalge). Especially prized was a sequence of eggs laid by the same bird throughout her life: each was identically marked with a design of splotches and scribbles. The extensive collections of early oologists, such as George Lupton, who amassed more than 1,000 guillemot eggs, fascinate Birkhead even as he laments this now illegal and inadmissible practice. He tracked down many old collections to learn more about the evolution of shape and colour. Through careful evaluation of alternative hypotheses, he dispels the common explanation that the pear shape of the guillemot's egg evolved mainly to keep it from rolling off the nest precipice. Rather, the shape probably provides legroom for the developing chick, enables the egg to tip above the faecal stew that often surrounds it, and increases surface area — improving heat transfer during incubation.

With equal thoroughness, Birkhead shows that the unusual markings — from light peppering, squiggling and blotching to completely blackened ends or dark rings around the midline — that entranced collectors enable guillemot parents to recognize their own eggs. This, however, is only part of the story of egg colour. Other species' eggs are marked to camouflage them: the Japanese quail (Coturnix japonica), for example, lays heavily mottled eggs in nest sites with matching patterns. Some eggs, such as that of the ostrich (Struthio camelus), are white to protect the developing chick from the heat of the Sun. Others are brightly coloured, as with the American robin (Turdus migratorius), whose blue eggs advertise the quality of the brooding female. Still others may be lightly pigmented to raise their internal temperatures or to increase light penetration, which can speed up chick development. This mechanism may be used to synchronize hatching within a clutch: the last eggs laid are often the lightest in colour. Through the eye of this careful evolutionary ecologist, and a series of high-quality colour plates, we come to appreciate the beauty and functionality of eggs.

Having considered the whole egg, Birkhead next describes its making. He writes clearly, with accuracy and wit, about the ovum's development in the bird's ovary and its journey through the oviduct. We learn about the microstructure of the shell — much like a rigid sieve — and how pores and cuticle adapt the egg to local atmospheric conditions, as well as repelling water, hydrophilic microbes and contaminants that can diffuse in and challenge the developing embryo. Foreign bodies that make it past the shell are dealt with in the albumen, which Birkhead describes as a “sophisticated biochemical firewall against microbes”. He then explains how the yolk provides fats and proteins manufactured in the mother's liver to the growing chick; it also furnishes the chick with crucial antioxidants, vitamins and hormones such as testosterone.

The embryo's survival may be enhanced by the odorous, oily secretions of the mother's preen gland that grease the eggs' shells during laying and incubation. In some species, such as the hoopoe (Upupa epops), this oil mixes with the copious droppings in the nest to produce a notorious 'filth', which may include beneficial bacteria that enhance hatchability. Conservation biologists working to restore rare species may find that the lack of such bacteria helps to explain why many eggs are difficult to hatch without at least a modicum of parental incubation.

Along the way, Birkhead introduces many colourful characters little known to science. Sequences of eggs collected from the 1970s to the early 2000s by John Colebrook-Robjent in Zambia were crucial to our understanding of the 'arms race' in egg coloration between nest parasites and their hosts. Birds such as cuckoo finches (Anomalospiza imberbis), for instance, sneak their eggs into the nests of others, but must continually adjust the background colour and pattern to fool the hosts — which in turn evolve unique markings to foil the parasite's disguise. Lupton's guillemot-egg collection inspired and informed current understanding of the adaptive value of egg shape. British physician Allen Thomson speculated that the yolk is built up in layers. Birkhead's ability to weave together history and science shows the human nature of research.

He has a marvellous way with words, writing of monogamous albatrosses living like “long-distance truck drivers — at home with their partner only occasionally and making the most of it when they are”. And he tantalizes with unsolved mysteries. Why, for example, does the egg of a chicken travel through the hen pointed end first until the very last minute, when it turns through 180° on the horizontal plane to be laid blunt end first?

Birkhead's historical acumen and sharp pen had me seeing eggs in a new light. He has convinced me that they are splendid, if not indeed most perfect.

Author information Affiliations John M. Marzluff is the James W. Ridgeway Professor of Wildlife Science in the School of Environmental and Forest Sciences at the University of Washington, Seattle. His latest book is Welcome to Subirdia. John M. Marzluff Authors John M. Marzluff View author publications You can also search for this author in PubMed Google Scholar Corresponding author Correspondence to John M. Marzluff.

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