2. Birds are streamlined (spindle-shaped) and most of them fly.
3. The pectoral muscles of birds are developed; Short rectum, large appetite and fast digestion, that is, the digestive system is developed, which helps to lose weight; The heart has two atria and two ventricles, and its heartbeat is fast.
The temperature of this bird is constant. In addition to the lungs, the respiratory organs also have airbags protruding from the lung wall to help the lungs breathe twice.
5. Birds are oviparous and have a high body temperature, usually 42℃. Birds have developed keel-like processes on their sternum.
Extended data
Living habits of birds:
1. Birds eat all kinds of food, including nectar, seeds, insects, fish, carrion or other birds. Most birds move during the day, and some birds (such as owls) move at night or at dusk. Many birds migrate long distances to find the best habitat (such as Arctic terns), and some birds spend most of their time at sea (such as albatrosses).
2. Flying Most birds can fly, and a few flat-breasted birds can't fly, especially the birds living on the island, which basically lose their flying ability. Birds that can't fly include penguins, ostriches, kiwis (a wingless bird from New Zealand) and extinct dodos. When humans or other mammals invade their habitats, these flightless birds, such as the great auk and the fear birds, will be more likely to become extinct.
Every spring and autumn, birds fly in groups in the sky, covering the sun. This seasonal phenomenon of changing habitats in different seasons, or moving from nesting sites to wintering sites, or returning from wintering sites to nesting sites is called bird migration. Every spring, birds begin a series of activities, such as courtship, reproduction, nesting, hatching and brooding.
References:
Baidu Encyclopedia-Birds-Morphological Characteristics
Baidu Encyclopedia-Birds-Living Habits