Birds: Masters of the Sky

Birds are warm-blooded animals covered in feathers. Like us, they have a backbone and breathe air with lungs. All birds share the same basic body plan: two wings, two legs, and a beak instead of teeth. But here is a surprise — not all birds can fly! Penguins use their wings to "fly" underwater, and ostriches cannot fly at all, instead running across open plains at up to 70 kilometres per hour.

Flight is hard work, so birds have bodies built to be light and strong. Many of their bones are hollow, filled with air instead of being solid, which makes the whole bird lighter without making it weak. Powerful chest muscles flap the wings, and a streamlined shape helps them slice through the air. This is why a bird the size of a cat can lift itself off the ground while a cat cannot.

A bird's beak is a brilliant tool, perfectly shaped for the food it eats. A long, curved beak is great for sipping nectar from deep inside flowers. A strong, hooked beak tears meat. A flat, wide beak scoops fish or filters tiny food from water. And a short, cone-shaped beak is just right for cracking open tough seeds.

Many birds build nests to keep their eggs and chicks safe and warm. Nests can be neatly woven from grass and twigs, scraped into the ground, glued to a cliff face with mud, or even hidden in a hole in a tree. Some birds skip the nest altogether — the emperor penguin balances its single egg on its feet and covers it with a warm flap of belly skin through the freezing Antarctic winter.