The largest and second-largest birds in the world are ostriches and emus. Both are flightless but capable of running at high speeds. In fact, their bodies have developed specifically for running, with legs, bodies and necks all balanced for quickly reaching top speed.
The average ostrich is both taller and heavier than the average emu. Most ostriches reach heights of 7 to 9 feet, while emus are normally between 5.5 and 6 feet tall. In addition to extra height, an ostrich has a massive body compared with that of an emu. An ostrich weighs between 220 and 350 pounds, while an emu weighs between 90 and 150 pounds. Among ostriches, males are usually larger than females; among emus the reverse is usually true, females usually larger than males. The size difference of these birds is reflected in their eggs. Ostriches lay the largest eggs in the world, averaging 3.6 pounds each. Emu eggs weigh less than half of that, averaging 1.5 pounds each.