Re: Why is the shape of an egg pointed at one end and not the other?

Date: Mon Dec 7 07:35:28 1998
Posted By: Jurgen Ziesmann, MadSci Admin
Area of science: Zoology
ID: 912987899.An

Message:

Eggs come in all Shapes

Eggs are not all the same shape as the chicken eggs that we eat. Even the shape of the domestic chicken egg is different from that of its wild ancestor, the Red Junglefowl. Some birds eggs are more pointed, or pyriform and, at the other extreme, some are more rounded or spherical.

Many Factors affect Egg Shape

Egg shape is determined by the internal structure of the hen. Her oviduct, distribution of internal organs and shape of her pelvic bones all affect egg shape. The Mallard's egg at the top of this picture is subelliptical (not quite spherical). The Great Horned Owl's egg is spherical and the Red-tailed Hawk's egg, at the bottom, is elliptical.

Consequences of Shape

Aristotle once suggested that males came from more pointed eggs and females from more rounded eggs. This of course, is not true. The shape of an eggshell does affect its physical properties, however. The general spherical shape of an egg maximizes shell strength while also conserving shell materials. More rounded eggs further maximize the volume of the egg for theamount of eggshell as well as ensure heat conservation.

The Ecology of Egg Shapes

Egg shapes, over time, are often closely matched to their nest environment. Shorebirds normally lay four pointed eggs. In the nest, the eggs are oriented with their pointed ends towards the centre. This minimizes the amount of space needed to form the nest and increases the efficiency of the heat transfer from parent to egg during incubation.

Murres lay one egg on a bare nesting ledge. Their egg is very pointed. If bumped, the egg is more likely to roll in a tight arc than to roll off the cliff.

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