The first of all the birds was the archeopterix lived about 140 million years ago, it was an animal that looked very much like a reptile, in fact their ancestors were reptiles just as these archeopterix had teeth and a long and bony tail. But it had feathers instead of scales, for this reason the scientists consider it a bird, the wings of the archeopterix were just like the wings of the birds of today, that is, bones inside and feathers on the outside.
But the arqueopterix could not fly very well, it did not shake its wings with force, it is more likely that it used them to plan.
A bird is every animal that has feathers, all birds have two legs and two wings except bats, they are the only animals with bones that can fly. The present birds do not have teeth, nevertheless they have a hard and elongated mouth that is called beak and serves to catch and eat its prey. All the female birds lay eggs and almost all build nests to hatch their eggs in them.
Birds, like people, are warm-blooded animals; The temperature of your body remains stable no matter how cold or how hot it is.
At present there are some 9000 kinds of birds, they can be found almost everywhere, except at the North Pole and the South Pole. The feathers serve to make the bird warm when it is cold, the bird inflates the feathers and under it a layer of hot air remains, the fluffy feathers make a blanket and keep your body warm. When it's hot, the bird does the opposite; crushes the feathers against the body to dissipate the heat.
The feathers also serve to fly, when it is flying, the bird uses the outermost feathers of the wings to propel itself. The feathers of the wings and tail serve to maintain balance, to change direction and to brake. The bright colors of the plumage serve the male to find a mate, the colors become even more vivid during the pairing season. Then he flies or parades in front of a female unfolding his beautiful plumage, sometimes sings and dances to attract attention.
Some male birds build eye-catching nests to attract the attention of the females and thus be able to procreate, the birds do not learn to build nests, they do it instinctively, every kind of bird is born knowing how to build their nest. Many build them in the shape of a cup, with grass and small branches.
The cardinals and the thrushes make this kind of nest, there are swallows that make them with clay balls, sticking you are on the walls of the mountains on the roofs of the houses. Some birds, like the turtle do their nest in a tree or rock hole, cover the bottom of the hole with grass, feathers and thigh. Certain weaver birds build stems and twigs true "apartments" very complicated, these nests can be 3 meters high and house up to 100 birds or more.
Translated from my post https://steemit.com/busy/@ceciliatorres/birds