Advanced Bird Nerdery

With the exception, perhaps, of the most dedicated vegan, all of us have cracked open an egg at some point in our lives: to scramble for breakfast, to make an egg drop soup, or, for those more reckless in our diet, to whip up a rich creme brûlée. Yet how many of us have ever paused to wonder about the complex mechanisms that go into the creation of the egg itself?

A 19th-century abolitionist named Thomas Wentworth Higginson once said, “If required on pain of death to name instantly the most perfect thing in the universe, I should risk my fate on a bird’s egg.” Author Tim Birkhead, a fellow of the Royal Society of London and teacher of animal behavior and science history, embraces this point of view and takes the reader on a journey of discovery about the mighty egg. He starts the odyssey from the outside, exploring the shapes of bird eggs and the hows and whys of color. He moves next to the albumen, which you know as the egg white, but which Birkhead knows as the major line of defense against dangerous microbes that could threaten the life of the embryo inside. Finally he discusses the yolk and explores the processes of laying, incubating, and hatching.

This book is fascinating. I hear you saying, “Sure, Kim, but aren’t you a self-proclaimed bird nerd?” Fair enough, but there is so much that I hadn’t considered about bird eggs before. For example, the utter perfection of the egg shell as protective armor for the chick inside. It has to be “strong enough to withstand the full weight of an incubating parent, but weak enough to allow the chick to eventually break free.” Have you ever considered how a baby bird breathes inside the egg? Unlike mammals, a baby bird isn’t connected to mom; it exists in a self-contained environment. Pores in the shell allow the baby to breathe; but here’s the amazing part: because gases behave differently under pressure, and loss of gases is reduced at higher altitudes, eggs laid at higher altitudes have fewer, smaller pores. This is true among birds of the same species and even the same individual birds as they move to different altitudes (this was demonstrated by a study done with chickens who were moved to different altitudes). Somehow, the bird’s body knows to adjust the number of pores depending on atmospheric pressure.

Being primarily familiar with chicken eggs, you may not realize the wide array of shapes, sizes, and colors eggs come in. I’ve always been interested in the cone-shaped eggs of murres and guillemots. For years I’ve been telling people that the cone shape prevents the eggs from falling off the cliffs where murres and guillemots nest, because the shape compels the eggs to roll in a tight arc. Not so fast, says Birkhead. Having spent years studying guillemots, he points out that the arc in which the egg rolls is still wider than the narrow cliffs on which those birds nest, and he’s seen witnessed enough startled guillemots to have seen plenty of eggs roll to their destruction. So what’s the point of the cone shape? Birkhead has his own hypothesis, and while I don’t want to spoil it for you, I will tell you it has to do with bird poop, of which you can find copious amounts in guillemot colonies.

Birkhead dedicates two chapters to egg coloration, addressing both the why and the how. In these chapters, I learned one of my new favorite words. Oocyan is the substance that gives many bird eggs their blue coloration and the moniker I’m going to select the next time I have to come up with a unique user name. In these chapters, he also contemplates the curious ability that guillemots have to produce a wide variety of different colors and patterns. (Birkhead is a guillemot expert; thus, they figure into many of his examples.) Chicken eggs are white and American robin eggs are blue, so why do guillemots produce such variety? Again, based on his research, he surmises it has to do with their lifestyle as colony nesters. It seems that guillemot moms learn the unique color and pattern of their eggs after laying, and so are able to distinguish their own eggs from their neighbors’.

To tantalize you further, consider these wonderful tidbits:

• Unlike a mammalian ovum, which locks out all subsequent visitors once fertilization by a single sperm occurs, a bird ovum can be penetrated by multiple sperm. In fact, it even seems that bird ova require multiple sperm for fertilization to occur.
• Some female birds store the male sperm, to be released when she is ready. This comes in handy for birds that are frequently apart, such as albatrosses
• Which end comes first, the blunt or the sharp end? In most cases, the sharper end travels down the oviduct first, then rotates 180 degrees, or “flips,” so that the blunt end emerges first.

I like Birkhead’s style of curious questioning. In a way, he encourages all his readers to become scientists. He describes his process when he contemplates a new problem, starting with “why this” or “why that.”  He writes, “For me, asking questions isn’t enough on its own; I need to go one or several steps further. Why this? becomes perhaps this. That is, I’ve formulated an hypothesis, a statement of what I imagine might be the explanation.”

The Most Perfect Thing is an excellent read for the curious minded. You’ll never look at an omelet the same way again.