What do you mean the cold city birds are flying?

Birds fly in the air in two ways. One is settled birds, which live in groups all the year round or are scattered around our lives and often fly around. Sometimes, flocks of birds fly in the air, and when they fly very low, it means that the weather is bad, rainy or overcast and humid. This means that there is little oxygen in the high places in the sky, but there is enough oxygen in the low places. The settled birds fly high in the sky, which means that there is enough oxygen in the high places. This can also be a weather forecast. Another situation is migratory birds. They fly in groups when the weather is warm in spring and fly away when the weather is cold in autumn. When it is hot, they come to our north for food, and when it is cold, they fly back to the south. Birds like geese and Xiaoyan.