Gillian Gibb: Why can't some birds fly?

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].

Many birds have independently lost the ability to fly, trading wings for survival advantages on the ground. Species like the cassowary and kiwi thrive by saving energy and adapting their bodies with dense bones and small wings. While flight helps escape predators, it also demands a huge energy budget and restricts size. On islands without predators, birds often become flightless within a few generations but remain vulnerable when new threats arrive.