The list of New Zealand birds by water is endless. Each bird has a part in the ecosystem and they have different levels on the food chain.
So each animal or life form is different from each other and the environment lives in a balanced fashion. If it is in a place where there are no introduced species that threaten some of the species.
If say for instance you live in a country Where there are no original cats or stoats, and you have birds that nest and live on the ground. The cats thrive and those birds will die because they have no defence.
This has happened to New Zealand and the very reason why many bird species are now extinct and some are an endangered species.
Some of these are around the world but happen to live in New Zealand and if they were introduced, became part and part of New Zealand today.