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Open my wish list →A bird's egg is a safe little home where a chick grows. Here are three true things about the shell around it.
Birds' eggs have a hard shell made of calcium carbonate. Bird eggs are oval, but how long and how lopsided they are depends on the kind of bird.
SourceThe shell is not completely sealed. Tiny pores in bird eggshells let the growing chick breathe, swapping gases with the air outside.
SourceAn egg's colour comes from pigments laid down on top of the shell. One pigment gives a green or blue colour. Another gives reds and browns, as a background colour or as spots.
SourceHatching day
A hatching chick has a tiny, sharp point near the tip of its beak, on the top part. This is its egg tooth. When it is close to hatching, the chick uses it to pierce the air sac between the membrane and the shell. The air in the sac lasts a few hours, and during that time the chick hatches. It pushes its egg tooth through the shell again and again as it turns. This is called pipping. In the end it cuts away a piece at the blunt end of the egg and climbs out. Some chicks, such as megapodes, do not need an egg tooth. They crack the egg open with their legs and feet. Later, the egg tooth falls off or becomes part of the growing beak.
SourceInside the egg
Inside an egg are the yolk and the white. The yolk gives the growing young the nourishment it needs. It sits inside a thin bag called a yolk sac, which is joined to the young bird as it grows. The yolks of birds' eggs are yellow because of colourful substances called carotenoids. Around the yolk is the albumen, or egg white. It is a clear liquid layer. It also works as a store of water for the young bird. More than half of the protein in egg white is one kind, called ovalbumin.
SourceStruthio camelus
Ostrich eggs are the largest of all eggs. On average they are 15 centimetres long and weigh 1.4 kilograms. They are glossy and cream-coloured, with thick shells marked by small pits.
SourceApteryx
The kiwi of New Zealand lays one of the largest eggs for its size of any bird in the world. The male keeps the egg warm, except in the great spotted kiwi, where both parents help. It takes 63 to 92 days to hatch.
SourceMellisuga helenae
The bee hummingbird lives in Cuba. The female lays two eggs at a time, each about the size of a coffee bean. She builds a cup-shaped nest about 2.5 centimetres across and keeps the eggs warm by herself for 21 days.
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