Avian eggs vary enormously in size, shape, and shell thickness across different species. Determining which bird lays the “biggest” egg depends entirely on the metric used: sheer physical volume or size relative to the mother’s body mass. This variation reflects the diverse evolutionary strategies birds have developed to protect and nourish their developing offspring.
The Absolute Winner: Biggest Egg Size
The largest egg laid by any bird living today belongs to the Ostrich (Struthio camelus), which is fitting for the world’s largest bird. An average Ostrich egg measures about 15 centimeters (5.9 inches) in length and 13 centimeters (5.1 inches) in width. These massive eggs weigh approximately 1.4 kilograms (3 pounds), making them the heaviest avian eggs on the planet.
One Ostrich egg holds the volume equivalent to roughly 20 standard chicken eggs. The shell itself is exceptionally thick, often measuring around 2.56 millimeters, which is necessary to withstand the weight of the incubating adults. This size ensures the developing chick has a substantial food reserve to support its rapid growth before hatching.
The Proportional Champion: Biggest Egg Relative to Body Size
While the Ostrich egg is the largest in absolute terms, it is one of the smallest relative to the size of the parent bird. The true champion for reproductive effort is the Kiwi, a flightless bird native to New Zealand. The female Kiwi lays an egg that is disproportionately enormous compared to her own body.
The Kiwi egg can constitute up to 20 to 25 percent of the female’s body weight just before it is laid. For a bird weighing only about 1.7 kilograms, an egg weighing over 400 grams is an extraordinary biological feat. This places an immense physiological demand on the mother. This massive egg size provides the chick with an unusually large yolk sac, allowing the hatchling to emerge fully feathered and highly independent.
Comparing Extremes: The Smallest Bird Egg
At the opposite end of the size spectrum is the smallest known avian egg, produced by the Bee Hummingbird (Mellisuga helenae). This tiny bird, native to Cuba, holds the record for the smallest bird species in the world. Its reproductive output is equally diminutive.
The Bee Hummingbird egg is about the size of a coffee bean, measuring 12.5 by 8.5 millimeters. It weighs as little as 0.05 grams, making it almost impossible to spot in the wild. This microscopic egg highlights the vast range of size variation in the avian world, contrasting sharply with the Ostrich’s output.
Extinct Giants and Historical Context
To find the largest egg in history, we must look to the fossil record and the extinct Elephant Bird (Aepyornis maximus) of Madagascar. This gigantic, flightless bird, which went extinct around the 17th century, produced eggs that dwarf those of the modern Ostrich.
Elephant Bird eggs are the largest known eggs of any vertebrate. These prehistoric specimens had a volume that could reach between 5.6 and 13 liters. They measured up to 40 centimeters (16 inches) in length and 25 centimeters (9.8 inches) in width. A single Elephant Bird egg was roughly seven times the volume of an Ostrich egg.