Before the first canoes arrived Hawaii was a kingdom of birds. Hawaii was a much different place prior to human contact. Birds and insects were the only land animals able to colonize this remote group of islands. There were no land mammals or reptiles. Under these conditions, flightless bird species evolved in the islands. The largest were "true geese" related to the Nene and Moa Nalo ("vanished fowl") related to babbling ducks. They lived all over the islands as recently as 1200-500 years ago. Now all are extinct.
It is very difficult to remove all predators from Nene habitat. Feral dogs and pigs must be hunted from large tracts of land or fenced out.