Question

what is the scientific reason behind bird's migration

Answer 1

Geese winging their way south in wrinkled V-shaped flocks is perhaps the classic picture of migration—the annual, large-scale movement of birds between their breeding (summer) homes and their nonbreeding (winter) grounds. But geese are far from our only migratory birds.

Answer 2

Geese winging their way south in wrinkled V-shaped flocks is perhaps the classic picture of migration—the annual, large-scale movement of birds between their breeding (summer) homes and their nonbreeding (winter) grounds. But geese are far from our only migratory birds.