The common guillemot is a bird with decidedly uncommon eggs. They're shaped in such a way that when they roll, they do so not in a long, wide arc but a tight, uniform circle. But why would an egg do such a thing?
Guillemots are seabirds, and they tend to congregate on the ledges of cliffs overlooking the ocean. The view is spectacular, but it's a pretty precarious place for a newly laid clutch of baby birds. Guillemots don't even build nests, and their breeding colonies are notoriously crowded – what's to keep an egg from getting knocked around and rolling over the edge of the nearest precipice? Answer: A shape that causes it to veer, in a narrow gyre, away from the edge and out of harm's way.
A crowded guillemot colony on the UK's Farne Islands | Photo Credit: gabrisigno.
It's reasonable to assume that the guillemot egg's shape is a rather elegant product of natural selection, and that the birds are perhaps descended from a cliff-dwelling ancestor with inferiorly shaped eggs. Those ancestors whose eggs were more conical in shape – and therefore more prone to rolling circularly – had their genes passed on in their surviving offspring. Those ancestors whose eggs were more spherical in shape may have literally watched their genetic legacy roll away, only to be dashed sad and yolky on the rocks below their cliffside roosts.
Not to harp on about this group of birds, specifically (the eggs of most birds tend to make for fascinating examples of natural selection – they vary tremendously in size, shape and color, and are incredibly adaptive), but the guillemot egg's shape is not its only remarkable feature. Guillemots nest in large groups, and the markings on each female's eggs are markedly distinct. This makes it easier for females to identify unhatched offspring as their own. (At left: some variegated guillemot eggs. Photo credit: Steven Portugal.)
Researchers also recently discovered that guillemot egg shells are composed of cone-like nanostructures that make them more hydrophobic than the eggs of most other birds. This water-repelling characteristic lends the eggs a "self-cleaning" quality. Water that falls on an egg's surface will bead and roll away, taking salt (deposited by the ocean breeze), feces (deposited by the birds) and dirt away with it. Free of these impurities, the an egg's shell can more effectively mediate the exchange of oxygen and carbon dioxide between the embryo and the outside world.
All-in-all, the guillemot's is one accommodating ovum.
Top animation via our favorite repository of nature gifs, Head Like and Orange.
[Via It's Okay to be Smart]