Birds have feathers on their bodies. They are good at flying and are of ovipara and homeothermal vertebrates. The most outstanding feature of birds is that they have feathers on their bodies; they have two wings and two feet. To have feathers is the endemic feature of birds. We can determine whether a kind of animal is a bird by observing whether they have feathers or not. Animals that have feathers must be birds. A kind of mammal, the bat, can also fly. But they are not birds because they have no feathers. Chickens and ducks, though lost their ability to fly after being raised by mankind, are still birds because they have feathers.
