You may not know: The elephant bird egg is the largest bird egg in history.

The elephant bird egg is the largest egg in history, measuring 33 cm long, as large as 150 - 180 chicken eggs.

The largest egg still in existence is still that of an ostrich. The largest ostrich egg ever laid weighed 2.589kg, about the same as a small house cat. The eggs are on average 15cm long and 13cm wide, but weigh just 1.4% of the weight of the female. This is unusually low for such a large bird. By comparison, female kiwis lay eggs that weigh between 15 and 22% of their body weight.

Ostrich egg (left) placed next to elephant bird egg. (Photo: Flickr).

However, the title of the largest egg in history belongs to the elephant bird ( Aepyornis maximus ), which roamed the island of Madagascar until 1,000 years ago. They laid eggs up to 33cm long, which can contain 8.5 liters of liquid, according to the Guinness Book of World Records.

Elephant birds weigh more than 450kg, the equivalent of 3 pandas, so it's easy to see why their eggs are so huge. However, to the naked eye, the eggs are still incredibly large. In 2018, the Buffalo Museum of Science discovered a 1.5kg elephant bird egg in their collection that they had previously mistaken for a fake.

"Antiquities and specimens that have been lost or misclassified in museums for centuries have been lost or misclassified. We were amazed to rediscover this rare egg in our collection," said Kathryn Leacock, director of collections at the museum.

Impressive as they are, the eggs' enormous size (about the size of 150 to 180 chicken eggs) may have contributed to their extinction. They were too attractive to humans, as evidenced by the many eggshell fragments found around ancient human campsites, suggesting that humans stole the eggs for food. Combined with habitat change and hunting, the elephant birds died out about 1,000 years ago, and the ostrich took over the title of the largest egg.