Kiwi’s habits and physical characteristics make them unbird-like in many ways. Sometimes they are referred to as an honorary mammal.
They build burrows like a badger, and sleep standing up.
The kiwi’s body temperature is lower than most birds, which range from 39ºC – 42ºC. The kiwi is more like a mammal, with a temperature between 37ºC and 38ºC.
The kiwi’s powerful muscular legs are heavy and marrow-filled, like a mammal, with skin as tough as shoe-leather. They make up a third of the bird’s weight. The skeletons of most birds are light and filled with air sacs to enable flight.
The eye sockets of most birds are separated by a plate, but in kiwi they are divided by large nasal cavities – just like most mammals.
While most birds depend on sight, the kiwi relies on a highly developed sense of smell and touch.
The kiwi’s sense of hearing is also well developed. Its ear openings are large and visible, and it will cock its head to direct its ear toward soft or distant noises.
Unlike most birds, which have one ovary, a female kiwi has two – like a mammal. If she produces more than one egg in a clutch, ovulation occurs in alternate ovaries.
The chick emerges from its enormous egg as a mini adult, fully feathered and able to feed itself – which is very unusual for a bird.
And finally, a kiwi’s plumage is shaggy and hair-like, and it has cat-like whiskers on its face and around the base of its beak. These super-sensitive way-finding whiskers are likely to have evolved to help the bird feel its way through the dark.