Emu Eggs Are Dark Green: The Pigment That Colors Them and Why

Emu eggs are a deep, dark green color, so saturated in fresh specimens as to appear nearly black. The color is produced by biliverdin, an endogenous bile pigment derived from the breakdown of heme during red blood cell recycling. Biliverdin is also the pigment responsible for the green component of bruise discoloration in humans: when subcutaneous hemoglobin breaks down, it converts through biliverdin (green) to bilirubin (yellow) before being reabsorbed or cleared. The emu eggshell applies this same molecule as a structural component during shell formation, producing a coloration that is not a surface coating but integrated into the outer layer of the calcium carbonate shell matrix. ## Biliverdin as an Eggshell Pigment Biliverdin and its reduced form bilirubin are the two principal pigments responsible for the non-white colors in bird eggs. Biliverdin produces greens and blues; bilirubin produces reds, browns, and yellows. The speckled and spotted patterns on many songbird eggs result from precise deposition of these pigments in the uterine shell gland during the rotation of the egg as the shell is formed. An egg that spins consistently in one direction while a pigment-secreting gland contacts it produces a streaked pattern; intermittent contact produces spots. In the emu, biliverdin deposition is dense and uniform rather than patterned, producing the deep green ground color. The intensity of the pigmentation varies across the incubation period: the shell fades from nearly black when freshly laid toward a more olive or brownish-green as the incubation proceeds and the outermost pigment layer degrades under UV exposure. This fading has been used by researchers as a rough indicator of incubation stage in field studies. ## Emu Egg Biology and Incubation Emu eggs are the second largest eggs in the world by weight after ostrich eggs, averaging around 600 to 700 grams, and measuring approximately 13 cm in length. A single female emu lays 5 to 15 eggs per season in a shallow ground nest. As with many ratites, incubation is handled exclusively by the male. The male emu sits on the clutch for approximately 55 days, during which he barely eats or drinks, losing up to a third of his body weight. He turns the eggs several times per day. The dark color of the egg may provide some camouflage benefit in the dim light of dawn and dusk when ground predators are most active, though the large size of the egg limits the effectiveness of coloration as a concealment strategy. More likely, the pigmentation intensity reflects the pigment load available from bile metabolism during shell formation rather than a strong adaptive signal. ## Emu Eggs in Human Use Emu eggs are commercially available in Australia and in specialty markets internationally, where emus are farmed primarily for oil, meat, and leather. The shell's thickness (approximately 1 mm, denser than chicken eggshell) and the striking color have made emu eggs popular substrates for decorative carving, a craft tradition in both indigenous Australian communities and contemporary artisan markets. Carved emu eggshells reveal a pale green or cream interior layer beneath the dark outer surface, allowing for two-tone relief work that cannot be achieved with the shells of most other bird species.