How did kiwi birds become flightless?

Kiwi have not yet died out. There are five recognised species, two of which are endangered.

There are several threats to the kiwi, which could result in this defenceless bird dying out in the future. Habitat loss and imported animals are the biggest threats. As is often the case, the introduced species have thrived, creating a threat to the native species which have less highly developed protective and defensive adaptations, having enjoyed a secure environment for thousands of years.

The kiwis' homeland, native forests and scrubs in New Zealand, are disappearing at an alarming rate due to clearing of forests for farming and agriculture, forest fires and introduction of imported animals. Due to the inability to fly, this makes kiwis vulnerable to their predators, which are usually land animals.

Not only is the loss of habitat a threat to the kiwis' food sources, but results in this small and defenceless bird having fewer places to hide from its many predators. Imported animals such as possums, livestock and deer eat trees, plant and seedlings, contributing to the clearing of forests, making it easier for mammalian and avian predators to access the habitat to prey on them.

The biggest threat to the kiwi comes from dogs and cats and other imported pets including the stoat, of all things. Being a small, flightless bird, the kiwi's defenses are extremely limited. Loss of habitat is also endangering the kiwi, not only as a threat to its food sources, but as the kiwi has fewer places to hide from its many predators. Prior to Europeans coming to New Zealand, the kiwi enjoyed a healthy population.