Question

what is the scientific reason behind bird's migration

Answer 1

Birds which breed in the summer in the extreme north such as the Arctic benefit from an abundance of food as plants and insect life flourish in the long daylight hours; and because few large permanent predators can survive the harsh winter. Many birdsthat breed in the Arctic simply lay their eggs on the ground

Answer 2

I think that a bird migrates because of the climatic changes in atmosphere