The Giant Moa as a species of giant emu that roamed the forests of New Zealand. You should know that when I say giant emu, I don't just mean a bit big, these things were basically frigging dinosaurs, standing at around 12 feet tall (that's twice the size of a velociraptor, FYI). In fact, since we've started to think that dinosaurs may well have had feathers, they could have been practically indistinguishable. Oh yeah, and they used to fight gigantic eagles too. Anyway, despite their monstrous size, humans had a go at these guys too and they were wiped out by Polynesian settlers who hunted them for food. Having survived as a stable population for at least 40,000 years, humans managed to deal with them in less that 300, as they were well dead by the time European settlers turned up (and promptly set about wiping out the local Mori population). Say what you like about the human race, we certainly know how to get things done. Particularly if it involves obliterating megafauna.