Bird eggs may be shaped by the way their mother flies

By Sam Wong

Eggs is eggs, but some are round while others are long and pointy – and now we finally know why. It’s all to do with birds’ flying ability, according to a new study.

There are many explanations for the variety of birds’ egg shapes. Take the idea that cliff-dwelling birds lay conical eggs that roll in a tight circle so they don’t fall off the cliff; or that clutch size dictates what shape of egg would make incubation more efficient.

To learn more, Mary Caswell Stoddard of Princeton University and colleagues analysed the shape almost 50,000 eggs from around 1400 species in museum collections. They quantified their shapes according to two measurements: the ellipticity, or length relative to width and the asymmetry, whether one end was pointier and the other rounder.

While elliptical eggs can be symmetrical or asymmetrical, spherical asymmetric eggs – like the shape of a hot air balloon – don’t seem to exist in nature.

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