WHICH BIRD LAYS THE BIGGEST EGG IN THE WORLD? 

Did you know that the Ostrich bird lays the biggest egg in the world, and that the myth that ostriches bury their heads in sand to avoid danger lies with the fact that ostriches keep their eggs in holes in the sand instead of nests?

The Ostrich is the biggest bird in the world and can weigh as much as 180 kilograms (kg). They also lay the biggest egg in the world, with one ostrich egg weighing about 1.4 kg which is equivalent to 24 chicken eggs. Interestingly, the ostrich egg is the smallest egg in the world in relation to their body size. The Kiwi lays the biggest egg compared to their body size.

The female common ostrich lays her fertilized eggs in a single communal nest, a simple pit, 30 to 60 cm (12–24 in) deep and 3 m (9.8 ft) wide, scraped in the ground by the male. The dominant female lays her eggs first, and when it is time to cover them for incubation she discards extra eggs from the weaker females, leaving about 20 in most cases. A female common ostrich can distinguish her own eggs from the others in a communal nest. 

Ostrich eggs, on average are 15 cm (5.9 in) long, 13 cm (5.1 in) wide, and weigh 1.4 kilograms (3.1 lb), over 20 times the weight of a chicken's egg and only 1 to 4% the size of the female. They are glossy cream-colored, with thick shells marked by small pits.

The eggs are incubated by the females by day and by the males by night. This uses the coloration of the two sexes to escape detection of the nest, as the drab female blends in with the sand, while the black male is nearly undetectable in the night. The incubation period is 35 to 45 days, which is rather short compared to other ratites. This is believed to be the case due to the high rate of predation. 

Typically, the male defends the hatchlings and teaches them to feed, although males and females cooperate in rearing chicks. Fewer than 10% of nests survive the 9 week period of laying and incubation, and of the surviving chicks, only 15% of those survive to 1 year of age.

A possible origin for the myth that ostriches bury their heads in sand to avoid danger lies with the fact that ostriches keep their eggs in holes in the sand instead of nests, and must rotate them using their beaks during incubation; digging the hole, placing the eggs, and rotating them might each be mistaken for an attempt to bury their heads in the sand.

The ostrich egg is also the strongest egg and this is to ensure that when the male and female ostriches sit on the eggs that they won’t break. A full grown man can stand on the ostrich egg and it will easily carry the weight of the person. One ostrich egg can take a pressure of up to 220 kg on the ends and 150kg on the side. Therefore, when one attempts to cook an ostrich egg it is quite a tricky proposition. To boil an ostrich egg can take up to 1.5 hours. Then after it’s cooked one has to open it. The shell of the egg is about 3 millimetres thick and one will need a saw to help “crack” it.

Sources: 

http://safariostrich.co.za/2017/09/the-biggest-egg-in-the-world/

https://en.m.wikipedia.org/wiki/Common_ostrich