Education: birds
Our feathered friends descended from dinosaurs are more than just pretty faces. Let’s learn more about them
BIRDS are two-legged warm-blooded vertebrates, which means they’re animals with spines. They’re also the only animals with feathers. All birds have wings, but a few species such as the ostrich can’t fly at all. Something that makes birds quite cool is that they’re descended from dinosaurs!
FROM PREHISTORIC TIMES
Birds belong to the Aves biological class and are found almost everywhere on Earth. They emerged during the Jurassic period (210-140 million years ago), evolving from dinosaurs of the suborder Theropoda (“animal feet”) and the clade (group of organisms) Maniraptora (“hand grabbers”).
These prehistoric birds had the characteristics of both birds and reptiles, such as teeth to tear off meat, and wings ending in talons. Today birds don’t have teeth. They do have a tongue but unlike the human tongue it contains a bone. Something else birds have in common with reptiles is they lay eggs.
FEEDING HABITS
Birds are constantly foraging. Like their dinosaur ancestors, some are meat-eaters – think of eagles and owls, for example – while birds such as the blue heron eat fish. But most birds feed on insects.
Some birds are plant-eaters and prefer fruit, such as the oriole and toucan, or grain, such as the weaver. The hummingbird is another plant-eater but favours nectar. Other birds such as the Indian myna are omnivores (plant- and meat-eaters).
Birds use their excellent vision to find food. Their beaks and claws are also adapted to help them access food, such as the hummingbird’s straw-like beak which helps it to suck up nectar or the woodpecker’s chisel-like beak which helps it dig into bark to find insects.
Humans benefit from the feeding habits of birds because they help to control insect infestations and pollinate flowers.
DESIGNED FOR FLYING
Birds are able to fly because they have a light skeleton and powerful muscles. Their feeding habits and cardiovascular and respiratory systems are also adapted to supply them with a lot of energy and enough oxygen. Like aircraft, birds have to negotiate four forces of flight to stay airborne – drag, thrust, lift and gravity. Apart from the shape of their wings, which provides thrust, birds also have other characteristics that help them to fly. Their streamlined body and sleek feathers reduce air resistance. Instead of heavy jaws with teeth they have a beak,
and their lightweight plumage and flexible, hollow bones also help them overcome gravity. A sturdy skeleton and enlarged breastbone allow space for the attachment of strong muscles that create thrust when the wings are flapped.
Flightless birds such as the penguin, kiwi and ostrich lost the ability to fly when they could no longer overcome the four forces. Kiwis lived on islands where they had no natural enemies so they didn’t need to fly.
In contrast, migrant birds such as the swallow can stay in the air for long periods and fly thousands of kilometres.