Ornithologists now agree that there is a very good reason why birds' eggs are generally narrower at one end than the other. What is the reason?

As an egg is formed inside a bird is soft until the shell is deposited on it.  The egg will therefore tend to take the shape of the cavity inside the bird.  It is probably also squeezed into this shape.

The evolutionary reason that is often cited is that the eggs will roll in a circle and not fall out of the nest.  Indeed, birds with more exposed nest (cliffs) tend to have eggs with more narrowing than those with less exposed nests (cavities.)

I don't know if I buy this because the rolling radius for a hen's egg is pretty wide.   It seems to me that an egg would have to be pretty sharply pointed to avoid rolling too far from the nest.  But maybe the selective pressure is pretty strong.

Posted by Jer on 2013-10-29 14:52:14