Birds such as wagtails, brown shrikes, pintails, ruddy shelducks, garganey birds, shovellors, mallards, herring gulls are not seen throughout the year because they have come from some parts of the globe for a certain period of time.
These birds are what we called migratory birds. The best place to see such migratory birds are certain wetland or riverine areas. The most striking feature of the migratory birds is that they come in flocks in enormous numbers and often swarmed the areas they visited.
Most of the migratory birds in India come from very far off places in the northern part of the globe, such as the palaerctic regions, across the high mountain ranges of the great Himalayas. Majority of the migratory birds coming to India are ducks, geese and cranes. Migratory ducks fly in an enchanting V-formation; maybe they have to save as much energy as they can because they have to travel a long distance during their migration