One reason is that until the arrival of humans a thousand years ago, there were no large land predators in New Zealand.
They need big, open grassy areas with access to water for protection against land predators.
Most penguins live on islands, shielded from land predators.
This is probably because penguins have no land predators in Antarctica or the nearby offshore islands.
No other extant land predator routinely takes on prey this large on their own.
The rails' life is made further hazardous by two introduced land predators, the Norway rat and the red fox.
There is still no clear explanation for exactly why these animals grew so much larger than the land predators that came before and after them.
The fishermonkeys were quick to rush into the water at the first hint of land predators.
For protection from land predators, the plains zebra retreats into open areas with good visibility at night.
The largest land predator in the world is the Bengal tiger.