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Feathers are the key to a bird s success, and 150 million years ago when they evolved from the dinosaurs, birds took to the air. But some have abandoned flight in a bid to take over the Earth as well. To survive, these flightless birds either have to be large enough to defend themselves, such as ostriches and emus, or to live on isolated islands where mammals cannot get at them. David Attenborough says that those birds living on the famous Galapagos Islands have no natural enemies there, so some birds don t bother to fly like cormorants with their stubby, useless wings. The immense island of New Zealand is paradise for flightless birds. The arrival of humans a mere 1,500 years ago was bad news for the birds, but even so, New Zealand gives us a rare glimpse of what the world would have been like if the birds had won the battle with the early mammals and now ruled the Earth.