Birds migrate to avoid cold winter and in search of enough food supply. They migrate in summer to avoid the heat and in search of proper nesting sites. Birds migrate from northern regions to the southern regions in autumn and early winter. They undertake their return journey during spring and early summer. Bird migration is a seasonal activity. They migrate in flocks happily in a V-shaped formation. They fly at a moderate speed ranging from 48km48km per hour to about 64km64km per hour. They generally fly at a height of under 900900 meters. They brave the dangers of being swept away by storms, being shot or captured. On the whole, bird migration is full of mysteries!