TED-Ed: Gillian Gibb: Why can't some birds fly?

Though the common ancestor of all modern birds could fly, many different bird species have independently lost their flight. Flight can have incredible benefits, especially for escaping predators, hunting and traveling long distances. But it also has high costs: consuming huge amounts of energy and limiting body size and weight. Gillian Gibb explores what makes birds give up the power of flight. [TED-Ed Animation by Anton Bogaty].