How Big Is an Ostrich Egg? The Largest Egg of Any Living Bird

Ostrich egg size in numbers

The ostrich is the biggest bird alive, and its egg holds the record too. Typical figures for a common ostrich egg are:

Eggs vary with the size and age of the hen and the subspecies, so some are noticeably lighter or heavier than the average. Animal Diversity Web describes a typical egg as about 6 inches long, 5 inches wide and 3 pounds in weight, equal to about 24 chicken eggs.

The shell is glossy cream or ivory, with a surface covered in tiny pits. It is thick and very strong, so it protects the egg from the weight of a sitting adult and from most small predators. Still, it is porous enough to let oxygen in and carbon dioxide and water vapor out.

Why is an ostrich egg small for the size of the bird?

Although it is the biggest egg in absolute terms, an ostrich egg weighs only about 1–4% of the female’s body weight. That is the lowest egg-to-body ratio of any bird. For comparison, a kiwi egg can weigh around 15–20% of the female’s weight, one of the highest ratios of any bird. Read more in How big is a kiwi egg?.

A small egg relative to body size makes sense for ostriches. Females lay many eggs over a season, often one every other day, and an egg that is cheap to produce lets them lay large clutches. Ostriches also share nests, so one pit can hold the eggs of several hens.

How ostriches lay and care for their eggs

During the breeding season, a male scrapes a shallow nest pit in the ground, which can be up to 3 m (10 ft) across. His main partner, the “major” hen, lays her eggs there first. Other “minor” hens add their eggs too, and a communal nest may contain anywhere from 15 to 60 eggs.

Not all of them can be incubated. The major hen recognizes her own eggs and moves extras to the edge of the nest, where they are less likely to be kept warm. Usually about 20 eggs are incubated. The work is shared: the gray-brown female sits during the day, when her color blends with the ground, and the black male sits at night.

After 35–45 days, the chicks break out. A newly hatched ostrich chick is about the size of a domestic chicken and can walk and follow its parents within days.

Danger is everywhere. Jackals, hyenas, birds of prey and other animals raid the nests, and Egyptian vultures are famous for throwing stones at the thick shells to crack them. Fewer than one in ten nests survives to hatching.

Is the ostrich egg the largest egg ever?

Not quite. The ostrich egg is the largest egg of any living bird, but several extinct birds laid bigger ones.

• Elephant birds of Madagascar laid the largest bird eggs known. They were about 26–40 cm (10–16 in) long, held several liters, and the biggest are estimated to have weighed around 10 kg (22 lb).
• Giant moa of New Zealand laid eggs up to about 24 cm (9.4 in) long, with surprisingly thin shells.

Both groups died out after people arrived on their islands. Find out more in What was the biggest bird ever?.

Among living birds, the next largest eggs after the two ostriches belong to the emu and the cassowaries. Emu eggs weigh about 450–650 g (1–1.4 lb) and are a striking dark green; see Why are emu eggs green?.

Ostrich eggs and people

People have used ostrich eggs for tens of thousands of years. Shells engraved with patterns about 60,000 years ago have been found at Diepkloof Rock Shelter in South Africa. Hunter-gatherers in the Kalahari have long used empty eggs as water containers, and beads cut from the shell are among the oldest known ornaments in Africa.

Decorated ostrich eggs have also been prized in other cultures, from ancient Mesopotamia and Egypt to Eastern Christian churches, where they are still hung on the chains of oil lamps. Today most ostrich eggs in shops come from farmed birds rather than the wild.

Ostrich egg facts

Fact: an ostrich egg is strong. Its thick shell must survive the weight of an adult bird of 100 kg (220 lb) or more sitting on the nest.

Fact: the ostrich yolk is often called the largest single cell. Strictly speaking, only the yolk of an unfertilized egg is one cell, but because the ostrich lays the biggest eggs alive, its yolk is often described as the largest single cell of any living animal.