Shorebirds and birds that nest on cliffs often lay eggs pointed on one end and rounded on the other, a teardrop shape when viewed from above. Some biologists think this shape allows the mother bird to cover eggs more efficiently when the pointed ends face inward, making the eggs fit together snugly. The shape also makes the eggs roll in a circle, which may be an advantage to birds nesting on flat, narrow ledges. Eggs vary in color from the pale white of tree-cavity nesters to the camouflaged speckles of species that nest on the ground. One of the great mysteries of oology is the American robin's sky blue egg, which seems an easy target for nest raiders.
Some scientists say birds' bodies are too hot for developing embryos.
Maybe live birth isn't all it's cracked up to be anyway. Eggs with shells seem to be working fine for the birds. This column is provided as a public service by the Geophysical Institute, University of Alaska Fairbanks, in cooperation with the UAF research community. Ned Rozell is a science writer at the Institute.