Cracking The Egg Mystery Of Fast Flying Birds

New research is indicating birds' eggs are a major factor in determining high flyers. For instance, based on a Sandpiper’s egg resembling a teardrop, a hummingbird’s looking similar to a jellybean and a owl’s like a golf ball, these characteristics provide clues as to how fast these birds can fly.

Extracting the data

According to Princeton University evolutionary biologist Mary Stoddard the shape of a bird’s egg depends on how much its species flies.

Stoddard's research team devised a computer program, called Eggxtractor for the purpose of selecting eggs based on their measurements in length, width, and shape. Out of 50,000 eggs, she and her colleagues used that data to determine how much each individual egg deviated from a perfect sphere. In other words, their intent was to distinguish those that were pointy and/or elongated. Some eggs are both pointy and elongated, some are one but not the other, and some are neither. But it was found that there were no eggs short and pointy.

New Theory

“There was an obscure hypothesis that egg shape could be related to flight ability that no one had paid any attention to,” Stoddard noted in her research.

Good flyers like sandpipers and murres tend to lay eggs that are more elongated and more asymmetrical—a bit like the shape of a Zeppelin—likely because lots of time in the air requires lightweight, compact bodies. Meanwhile, birds that spend little or no time in the air, like tropical pittas and trogons, have more spherical eggs.

So what connects flight to egg shape? This research indicated birds want to pack as many nutrients as possible into their eggs. But, in order to fly, they must maintain sleek bodies — meaning their eggs can’t be too wide or round.

Research & Bird Evolution

Stoddard noted a couple of distinguishing factors. For one, understanding egg shape “could be of value to the egg industry,” she says, perhaps by helping it create more durable eggs.

However, for her just solving the puzzle of egg diversity is a reward in and of itself. “Eggs aren’t just a favorite breakfast food,” she explains. A specialized egg, like that of modern birds, made it possible for developing young to survive on land, she notes, and thus allowed our land vertebrate ancestors to leave the seas about 360 million years ago. “They kick-started a revolution.”

Ultimately, this study shows “we can challenge old assumptions,” Stoddard said. ”In something as familiar and common as a bird egg, we are still discovering new truths.”

Mary Caswell Stoddard
Mary Caswell Stoddard heads up new research on egg shapes