The primary aim of migration is to take advantage of the longer days of the northern summer for breeding and to feed their young and to avoid harsh winters. The extended daylight hours allow diurnal birds to produce larger clutches of eggs than those of non-migratory species that remain in the tropics all the year round. As the days shorten in autumn, the birds return to warmer regions where the available food supply is more. During northern winters there is little food and cold temperatures, whereas in south, there is more food and less cold.
Between 1500 and 4000 species of birds are known to migrate. In India and South Asia, out of over 2000 species and sub-species, about 350 are migrants. It is estimated that over 100 species of migratory birds fly into India, either in search of food or to escape severe winter of their native habitat. In the Indian subcontinent the majority of migratory birds are winter migrants.
The first naturalist to write about migration was Aristotle, who studied pelicans, turtle doves, swallows, quail, swans and geese as migrants and observed that all migrating birds fatten themselves up before migrating. Every year, during autumn and early winter, birds travel from there breeding grounds in the northern regions of Asia, Europe and America to the southern lands of Asia, Africa and South America. They make the return journey again during spring and early summer.
Birds of prey, Swallows and Crows migrate in daytime, whereas thrushes, warblers, cuckoos, woodpeckers and most songbirds migrate by night. Large birds fly faster than small birds. Ducks and geese maintain an average speed of 64-80 km/h, while hawks and ravens fly at 35-45 km/h. Most birds migrate at an altitude of 3,000 feet or less but cranes and geese migrate at altitudes of 15,000-21,000 feet.
Before migration birds eat more food and store it as fat for their long journey. Some migrants almost double their body weights by storing fat before migration. The ruby-throated hummingbird weighs only 4.8 grams and can use stored fat to fuel a non-stop, 24-hour flight across a 600 mile stretch of open sea from the U.S. Gulf coast to the Yucatan Peninsula of Mexico.
The Arctic Tern(Sterna paradisaea) is a sea bird that breeds in Arctic and sub-Arctic regions of Europe, Asia, and North America in marshes, tundra lakes and shorelines. The species is strongly migratory, seeing two summers each year as it migrates from its northern breeding grounds to the oceans around Antarctica and back, covering a distance of about 38,000 km each year that take 90 days each side. This is the longest regular migration by any known animal.
The arctic tern flies as well as glides through the air, performing almost all of its tasks in the air. Arctic Terns are mainly grey, with red beak and feet, white forehead, a black-nape and crown and white cheeks. It is one of the most aggressive birds that fiercely defend its nests and young. Arctic terns leave the Arctic Circle and head eastwards across the Atlantic Ocean, flying down the west coasts of Europe and Africa.
In spring they fly north back to the Arctic, following the east coasts of South and North America. Considering an Arctic tern lives up to 30 years, a single bird may travel more than 650,000 miles in its lifetime. The young stay in the southern hemisphere until they are about two years old and will then migrate back to their birthplace. One Arctic Tern, ringed as a chick on the Farne Islands off the British east coast, reached Melbourne, Australia in just three months from fledging, a sea journey of over 22,000 km. The arctic tern may hold the record for longest migration distance since it flies about 35,000 km each year travelling between its arctic breeding ground and non-breeding area in the Antarctic.
Pied Crested Cuckoo (Clamator jacobinus) migrates to large areas in northern India in monsoon and has often been called the harbinger of monsoon or “rain visitor” from Africa. They move across the Arabian Sea and Indian Ocean to reach India in May or June. Some believe that the bird uses monsoon winds to assist its flight during this migration. It breeds during June-August and leaves the subcontinent in September/October for Africa.
The Common Cuckoo (Cuculus canorus) is a widespread summer migrant to Europe and Asia, and winters in Africa. It is a brood parasite, which lays its eggs in the nests of other bird species, such as meadow pipits and reed warblers.
The American Golden-Plover (Pluvialis dominica) breeds in Arctic Tundra and has a long, circular migration route. In the fall it flies offshore from the East Coast of North America non-stop to South America. It leaves the breeding grounds in early summer, but juveniles usually linger until late summer or fall. Some adults arrive on the wintering grounds in southern South America before the last juveniles have left the Arctic.
On the return journey in the spring it passes primarily through the middle of North America to reach its arctic breeding grounds. The bird has one of the longest known migratory routes of over 25,000 miles, of which 2,400 miles is over ocean where it cannot stop to feed or drink.
Manx shearwater (Puffinus puffinus)nests in a small number of island colonies from the Western Islands, Iceland, in the Faroes, in northern and western Britain and Ireland, Brittany, to the Azores, Madeira and the Canaries.
They nest in burrows, laying one white egg which is only visited at night to avoid predation by large gulls. They form life-long monogamous pair-bonds. Young Manx Shearwaters go to sea at night, without their parents, and immediately head for the winter quarters off the coast of southern Brazil and Argentina. Ringing studies in Stockholm show that some of the young make this 6000–7000 mile journey in less than a fortnight.
Manx Shearwaters migrate over 11,000 km to South America in winter, using waters off southern Brazil and Argentina, so this bird has covered a minimum of 1,000,000 km on migration alone in its lifetime. Another bird ringed in 1957 and breeding on Bardsey Island off Wales was calculated by ornithologist Chris Mead to have flown over 8 million km during its life.
Penguins. After breeding most penguin species moult, relying on fat reserves to sustain them for a period of 2-5 weeks without food. After moulting, penguins can enter water to find food and migrate. All penguins, except six species that are adapted to inshore life, migrate over long distances and return to land only for the breeding season.
Satellite telemetry of Adelie penguin migration shows that these birds travel a path along the coastline of the Antarctic continent to a winter feeding ground in an area north-west of the Balleny Islands, off the Ross Ice Shelf, a distance of 5,500 km. Tracking of Humboldt penguins revealed that most stayed within a 90 km radius of the island on which they breed. Migration is also the time when penguins are most vulnerable, with annual survival estimates ranging from 75% for the Little Penguin to 95% for the Emperor penguin.
Bar-tailed Godwit (Limosa lapponica) is a large wader in the family Scolopacidae, which breeds on Arctic coasts and tundra mainly in the Old World, and winters on coasts in temperate and tropical regions of the Old World. It makes the longest known non-stop flight of any bird and also the longest journey without pausing to feed, 11,680 kilometres along a route from Alaska to New Zealand.
It was shown in 2007 to undertake the longest non-stop flight by any bird. Birds in New Zealand were tagged and tracked by satellite to the Yellow Sea in China. According to Dr. Clive Minton, the distance between these two locations is 9,575 kilometres but the actual track flown by the bird was 11,026 kilometres. This is the longest known non-stop flight of any bird. The flight took approximately 9 days. At least three other Bar-tailed Godwits also appear to have reached the Yellow Sea after non-stop flights from New Zealand.
Albatrosses. Albatrosses are roaming seabirds that live up to 60 years, spending many continuous years at sea before returning to land to breed. Young birds leave New Zealand waters and fly circumpolar through the Pacific, Indian and Atlantic Oceans before returning to New Zealand waters to breed as adults when 6-10 years old. Satellite transmitters have been put on wandering albatross and have shown that birds can travel an incredible 700 kilometres a day.
Unfortunately, they also reveal huge losses to long line fishing. The Wandering Albatross, Snowy Albatross, or White-winged Albatross, Diomedea exulans,is a large seabird, which has a circumpolar range in the Southern Ocean. Based on tracking the precise movements of 22 birds, reveals that males are most likely to circumnavigate the world, with the fastest managing a distance of 14,000 miles in 46 days – the equivalent of a steady 13mph. More than half then made amazing round-the-world journeys – the fastest in just 46 days.
As the loggers only provide two positions per day, an accurate estimate of the distance is impossible but it is likely to have been at least 14,000 miles. Using satellite telemetry scientists have learned that some parent birds fly as much as 1000 kilometres per day, covering anywhere from 2900 kilometres to an astonishing 15,000 kilometres in a single foraging flight.