The kiwi has some of the characteristics of mammals, making it unique among birds. In the first place, the kiwi is covered with a wiry material that resembles hair rather than feathers. Also, unlike other birds, its skin resembles that of mammals in that it is leather-like and tough to penetrate. The kiwi has claws similar to a cat's and its bones are heavy like a mammal's, not light and porous like a bird's. Another interesting fact is that the kiwi has nostrils for breathing at the end of its beak.
Kiwis lay enormous eggs that are about six times as large as normal for birds their size. During her gestation time, the female kiwi eats three times more than usual and her belly becomes so large that it touches the ground. Despite the large size of the egg, they are usually laid quickly, and after they are laid the male takes over. He will incubate the egg and protect it until it has hatched. Kiwi eggs contain much more yolk than those of any other bird. Chicks are born with a large external yolk sac that they use to nourish themselves for the first 10 days of life by absorbing it through their navels.
When kiwis hatch they are like small adult birds. While most other birds emerge with a coat of down and closed eyes, kiwis are completely feathered and their eyes are open. At birth, they have soft beaks that are not strong enough for eating. However, this is not a problem because the parent birds do not feed their newborn chicks. By the time the chicks are no longer nourished by their yolk sacs, their beaks are strong enough to manage food. Kiwis grow very gradually and do not actually leave their parents to make their own homes until they are approximately four years old.
As soon as a kiwi is old enough, it will first establish its own territory. It finds a secluded place on the ground and then creates a burrow in which to live. The burrow is hollowed out of the ground. The kiwi does not build a nest like other birds. Because the kiwi is nocturnal, it will sleep in the burrow throughout the day and then leave it to search for food at night.