Why Are Emu Eggs Green? Color, Size and Shell Facts

What makes an eggshell green?

A bird eggshell is made mostly of calcium carbonate, which is naturally white. Colors are added inside the female’s shell gland, the part of the oviduct that works a bit like a uterus, while the shell is being built. Two main pigments are involved:

• Biliverdin, a blue-green pigment related to bile, which forms when the body breaks down heme from old red blood cells. It gives eggs a blue or green ground color.
• Protoporphyrin, a reddish-brown pigment that makes brown eggs and brown speckles.

The mix and amount of these pigments, and how deep in the shell they lie, decide the final color. The same blue-green pigment colors the eggs of many songbirds, which is covered in Why are robin eggs blue?. Emu eggs carry so much of it in the outer shell that the green becomes very deep.

Why do emu eggs look almost black?

The shell of an emu egg is built in layers. The outermost layer is the darkest, a bluish green that can look black on a cloudy day or in shade. Underneath, according to the Australian Museum, are paler green and white layers. The surface is also rough and granular rather than glossy, which makes it look even darker.

These layers are why carvers love emu eggs. By scraping through the dark outer layer to the lighter ones beneath, artists can create cameo-like pictures in several tones. Engraved and mounted emu eggs became a popular Australian decorative art in the 19th century and are still made today.

Do emu eggs change color?

Yes. Fresh emu eggs are at their darkest when laid. Exposed to sunlight, the outer pigment slowly fades, so eggs become lighter over time. Eggs that never hatch and are left behind in the nest can be bleached by the sun to a pale color; the Australian Museum notes that this takes about three months.

Within a nest, the eggs are mostly kept covered by the incubating father, so they stay fairly dark until hatching. Our article Do male emus sit on the eggs? explains how the male guards them for about eight weeks.

Why are emu eggs so dark?

Nobody has a complete answer. In many birds, egg color is thought to help with camouflage, signal the female’s condition, or affect how much sunlight and heat pass through the shell. For emus, a dark egg may be harder to spot on a ground nest, especially as emus nest in the cool winter months and the eggs sit among dark leaf litter and shadow. However, the eggs are almost always covered by the male, and scientists have not settled why emu eggs are so heavily pigmented.

What is clear is that the color is typical of the species: emus everywhere lay dark green eggs, whether wild or farmed.

How big are emu eggs?

Emu eggs are among the largest eggs of any living bird. They measure on average about 13 × 9 cm (5.1 × 3.5 in) and weigh 450–650 g (1–1.4 lb). The shell is around 1 mm (0.04 in) thick.

A female lays a clutch of about 5–15 eggs, one every two to four days, usually between April and June. The yolk makes up a large share of the egg, around half its contents, which supplies the chick through the long eight-week incubation.

How do emu eggs compare with other ratite eggs?

Emus belong to the ratites, a group of flightless birds that lay some of the biggest eggs on Earth. Their eggs come in surprisingly different colors:

The ostrich lays the largest egg of any living bird, but the emu’s dark green egg is the most striking in color. For a full side-by-side look at the two birds, see emu vs ostrich, and for the bird itself, visit our emu profile.

Myths about emu eggs

Myth: emu eggs are green inside. Only the shell is colored. The yolk and white look like those of any other bird egg.

Fact: emu eggs are used for food and art. Emus are farmed in Australia, North America and elsewhere, and their eggs are sold both for eating and as shells for carving and decoration.