Its smooth, thin, white or greenish-white shell is about 120-millimetres long and 80-millimetres in diameter – six times as big as normal for a bird the kiwi’s size.  Kiwi could be expected to lay an egg about the size of a hen’s egg.  In fact, the kiwi egg is almost exactly the size of eggs produced by the now-extinct bush moa.  This has led to speculation about whether the kiwi was once a very much larger bird.

Kiwi eggs also contain the largest proportion of yolk of any bird – 65 per cent, compared to most birds’ 35 – 40 per cent.  This means a bounty of nourishment for the newly hatched chick, which can feed off the yolk for the first week of its life.

Huge Effort to Produce a Huge Egg

Producing such a mammoth nutritious egg is a tremendous feat for the female kiwi, and she must eat three times as much as usual.  It takes 30 days to form the egg.

The egg makes up 15 - 20 per cent of her body mass and her pregnant belly bulges so much it touches the ground.  The female has to walk with her legs wide apart to accommodate it. Sometimes a female will soak her belly in cold water when heavy with egg - to soothe the inflamed stretched skin and temporarily relieve the weight.

Most Clutches are One Egg

In most varieties of kiwi, typical clutch size is one egg.  This is usually laid two-to-three weeks after mating.  Just before it is laid, the huge egg almost fills the female’s body, leaving little room for food in her stomach. Female kiwi therefore fast for two or three days before laying.

	Although enormous, the egg is laid quickly and, in some species, the female’s work is then done. She leaves the burrow and the male takes over incubating the egg.
Southern Tokoeka Kiwi Egg

If she is to lay another egg, this will already have begun to develop inside her, and will be laid about 25 days after the first egg.  It is rare, but not unknown, for a third egg to be produced, especially if one of the first eggs is lost. The most prolific egg producer is the Brown Kiwi which will often lay two-to-three clutches each year.

A female kiwi can lay up to 100 eggs in her lifetime.

Next: The male incubates the egg