In New Zealand birds thrived in the complete absence of predatory mammals. New Zealand became a place where birds could experiment with different kinds of behaviour, shape and size - a process scientists call 'adaptive radiation'. Birds used this freedom to occupy niches that elsewhere were filled by mammals.

Kiwi, like badgers and shrews of the Northern Hemisphere, left their burrows at night to sniff out insects and other food on the forest floor. Because of its behaviour and a number of physical features, including whiskers, 'hairiness', scent glands and nostrils for sniffing out food, the kiwi has been called the bird world's 'honorary mammal'.