Avian eggs exhibit a remarkable spectrum of colors and patterns, though most people are familiar only with the common white or brown shells found in grocery stores. The natural world holds exceptions, including some of the largest eggs produced by any bird species. These unusual eggs possess a deep, intense pigmentation that leads them to be described as black. This deep coloration is tied to the unique life history of the bird that produces it.
The Bird That Lays Large Black Eggs
The bird most accurately fitting the description of one that lays a large, black egg is the Emu, the second-largest living bird native to Australia. Its eggs are not truly jet black, but rather an incredibly deep, dark green that often appears near-ebony to the human eye. An Emu egg is substantial, weighing between 500 and 700 grams, which is roughly equivalent to a dozen average chicken eggs.
The Emu eggshell is notable for its robust, granular texture and multi-layered composition. The outer layer is the darkest, a striking emerald or jade color. Emu reproductive behavior is distinct: the female lays her clutch of five to fifteen eggs and then leaves the male to perform all parental duties. The male Emu incubates the eggs for about 56 days, relying on the egg’s cryptic coloration to camouflage the nest.
A closely related candidate is the Cassowary, a solitary, flightless bird found in the tropical forests of New Guinea and Australia. Cassowary eggs are also very large and dark, typically a vivid, deep green or pale green-blue. The male Cassowary takes on the full responsibility of incubating the three to eight eggs per clutch and rearing the chicks for up to nine months. Both the Emu and Cassowary eggs are among the largest avian eggs, and their dark hue is a shared trait among these ratites.
How the Dark Shell Gets Its Color
The intense, dark coloration of the Emu and Cassowary eggshells results from the concentration of specific pigments deposited during the egg’s formation within the female’s oviduct. The primary pigment responsible for this deep hue is biliverdin, a green bile pigment derived from the breakdown of red blood cell heme. This substance is integrated into the calcium carbonate matrix of the shell as it calcifies.
Biliverdin is also the pigment that gives the eggs of robins and some other songbirds their blue or blue-green color. In the Emu, however, the pigment is deposited in a much higher concentration throughout the entire thickness of the outer shell layer, creating a dark, almost black finish. The color is not merely a superficial coating but is chemically bonded within the structure of the shell itself.
This process begins in the shell gland, or uterus, where the egg spends the final hours of its development. The continuous secretion of biliverdin ensures that the dark color is uniform and deeply saturated. This high pigment load is a defining feature of these large ratite eggs, distinguishing them from the lighter green or blue eggs of other species.
Distinguishing Large Black Eggs from Dark Eggs
The uniqueness of the Emu egg lies in the combination of its enormous size and its intense, near-black pigmentation. While the Emu egg is dark green, other birds lay eggs that might be mistakenly described as black, but they lack the same scale or color intensity. For example, some chicken breeds, such as the Marans, are prized for laying eggs with a very deep, rich chocolate brown shell.
These dark brown Marans eggs owe their color to a different pigment, protoporphyrin, and are significantly smaller than the Emu egg. Certain Cayuga ducks occasionally lay eggs that appear black, particularly at the beginning of the laying season. This black appearance is often due to a superficial dark film or “bloom” that can be washed off, revealing a lighter shell color underneath.
The Emu and Cassowary eggs are distinct because their size is measured in hundreds of grams and their dark color is a permanent, structural component of the shell, not a temporary coating. This combination of being both physically large and possessing a uniformly dark, structural pigmentation is what makes them the natural answer to the search for the bird that lays a large black egg.