Some people speculate that these characteristics are a result of kiwi’s evolution in mammal-free New Zealand.  This meant it developed to fill niches filled by mammals elsewhere.

Great Sense of Smell

First, the kiwi is the only bird in the world with external nostrils at the tip of its beak. Its sense of smell is exceptional, second only to the condor, and not by very much.

It can locate food by smell alone.  This is thanks to a very well developed olfactory bulb.

 

Second, the kiwi’s sense of hearing is also well-developed. Its ear openings are large and visible, and a kiwi can often be seen cocking its head to direct its ear at soft or distant noises.

Marrow-filled Bones and Fleshy Footpads

Third, the kiwi skeleton differs from that of other birds, including other ratites. Undeveloped flight muscles give its body a cone-shape, topped with a strong neck and a small head. 

Like other ratites, the kiwi does not have a keeled sternum to hold the flight muscles, but it has gone a step further. Because it does not fly, its bones do not have to be super light.  So, instead of air sacs, the kiwi’s bones contain marrow. This makes the kiwi's legs powerful and muscular - they make up a third of its total weight.  And, unlike the other ratites, the kiwi has four toes instead of only two or three.

Its large, dinosauric feet mean it can walk almost silently, its tread muffled by fleshy footpads

 

Fourth, the kiwi’s eye sockets are not separated by a plate as most birds are.  Instead, they are divided by large nasal cavities – just like most mammals.  Kiwi eyes are small, and are built for nocturnal habits, but they can see well in daylight, and some Southern Tokoeka on Stewart Island emerge from their burrows to forage by day.

Low Blood Temperature

Fifth, kiwi’s blood temperature is much lower than most other birds which range from 39^oC - 42^oC.  The kiwi is more like a mammal, with a temperature between 37^oC and 38^oC.

Sixth, females have two functional ovaries, unlike other birds… and more like a mammal.  If a female produces more than one egg in a clutch, ovulation occurs in alternate ovaries.

Seventh, they build burrows like a badger.

Eighth, its plumage is shaggy and hair-like and it has cat-like whiskers on its face and around the base of its beak – like a mammal.