Simplify the following text for a Grade 7 native English-speaking person.
Original: Haast 's Eagle ( Harpagornis moorei ) was a species of massive eagles that once lived on the South Island of New Zealand .
Simplified: The Haast 's Eagle ( Harpagornis moorei ) was the largest eagle ever to have lived and is the only eagle in the world ever to have been top predator of its ecosystem . It lived on the South Island of New Zealand .