Winter in the south is also very cold. Why do migratory birds fly south in winter?

For birds, the priority is not cold, but whether there is food! When migratory birds fly south, we often feel that the north flies south, but where is the north and where is the south. Snowflakes migrate from the Arctic Circle to the Northeast for wintering, white-waisted crested finches migrate from the Northeast to North China for wintering, cranes migrate from the Northeast to the Yangtze River Basin for wintering, ostriches and other bird migration wintering in South China and Indochina Peninsula, snipes migrate to Australia, and Amur falcons and common dew swallows migrate to southern Africa. Is it cold in winter in Northeast China? There are also many winter migratory birds. Birds look for wintering places, mainly to see food. Therefore, those who eat fruits and grass seeds tend to overwinter in the north, while those who eat insects tend to overwinter in the south. If there is enough food in this area, many birds will not migrate. The best example is the red-crowned crane in Hokkaido, Japan, which has stopped migrating because of artificial breeding. Someone asked, since there is enough food in tropical and subtropical areas, why do birds fly back to the north to breed? That's because the northern summer has long sunshine hours and more hunting time, which is conducive to better reproduction and brooding. In fact, migration and reproduction are also closely related. In order to adapt to flight, the gonads of birds generally develop seasonally (it is random to fly like chickens), and the gonads of migratory birds generally mature after migration, and then reproduce in estrus ..... The advantage of this trait is that: in evolution, migration eliminates those "not so good" genes and improves the genetic quality of the population, which is beneficial in evolution. Behavior: In the animal kingdom, for example, some birds often begin to pair when they overwinter collectively. More importantly, winter migration is to transfer fertile individuals to places suitable for breeding in the next spring, in other words, to create advantages in time and space for breeding in the next year. In low latitudes, spring comes earlier, breeding can start earlier, brooding time is more abundant, and food is more abundant. Imagine that when the breeding of migratory birds in the south has been carried out for more than half, some high-latitude areas are still too cold, and the advantages are immediately reflected. Of course, flying back to the north takes time and sacrifices some individuals. However, this is another natural selection ... bird migration can be called bird habit. They are passed down from generation to generation, that is, the impulse to migrate is an innate instinct. Birds can get hints of migration from their own kind or from their keen senses. Every migration season, we can know that birds are always unstable, and they should be bound by a routine. Through observation, we can know that they are displayed by caged birds who don't know that there is winter and have never traveled. We can know that the migration of birds is brought by their talent, not "experience". The migration of birds can be called the habit of birds. They are passed down from generation to generation, that is, the impulse to migrate is an innate instinct. Birds can get hints of migration from their own kind or from their keen senses. Every migration season, we can know that birds are always unstable, and they are bound by a routine. Through observation, we can know that they are displayed by caged birds who don't know that there is winter and have never traveled. We can know that the migration of birds is brought by their talents, not classics.