Scientists believe they know why birds' eggs are different shapes. Some eggs are quite round; some are kind potato-shaped; and others are longer and pointy. Two thousand years ago, the Greek philosopher Aristotle said flatter eggs had female chicks inside them and rounder eggs contained male chicks. But he was wrong. A new study Princeton University the USA suggests that the shape the egg depends how well and how fast the female bird flies. Professor Mary Stoddard said: "It has not gone unnoticed that birds have evolved to [lay eggs ] shapes that are quite diverse form - everything a spherical owl egg to a pointy sandpiper egg."
Professor Stoddard and her colleagues created a mathematical formula to map the shape different eggs. They looked almost 50,000 eggs 1,400 different bird species. The researchers put the shape, length and height the eggs a computer database. They also looked how oval the eggs were. The researchers found that the birds that laid the most-oval-shaped eggs were the best fliers. Professor Stoddard said: "We were shocked to see that one the best explanations egg shape variation was flight ability." The researchers found that hummingbirds and sandpipers laid the most-oval-shaped eggs; owls laid the roundest eggs; and sea birds laid the pointiest eggs.