Why do flightless birds go extinct so often?

“Some island hotspots where flightless birds were prevalent include New Zealand, with 26 species, and Hawaii, with 23 species, all of which are now extinct.”

“Moas

The moas were the last of the giant species to vanish. A group of people known as the Māori were the first settlers of New Zealand. Between 1250 and 1350, the ancestors of the Māori hunted all of the 11 known Moa species to extinction. They used its eggshells as water carriers, while the bird’s meat and eggs would feed the village. Additionally, spears, hooks and ornaments were made by utilizing the Moa’s bones. When a species is hunted during all of its life stages, it has almost no chance of survival.”

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