Plus

Plus

Fly away
By K.G.H. Munidasa
Bird migration is a natural phenomenon that takes place about twice a year, in autumn and spring. In the Northern Hemisphere birds leave their nesting grounds near the Arctic regions or in the temperate zone with the advent of autumn (September to November) and move south. The following spring (March to May) they commence their northward flight along regular routes to reoccupy the territories they vacated six months ago.

Although east to west migrations may sometimes be observed, the general direction of flight is from north to south. Various theories have been put forward to explain bird migration. But it is accepted that it is connected to food. Birds are compelled to leave their habitats in the winter and fly south to the tropics where food is in abundance at all times. They return to their home territories when conditions are favourable.

There are roughly over 30,000 species and sub-species of birds, and nearly half of them migrate regularly. The migrant birds have two habitats - one to nest and breed and the other to rest and feed. These habitats are often thousands of miles apart in different climatic belts and continents. Yet twice a year they travel between them, either alone, in scattered parties, or in massive flocks. They fly by day as well as by night, over land masses and open seas, across lofty mountains and deep valleys or wide deserts, converging onto accustomed routes favoured by multitudes of migrants before them.

It is believed that day-flying birds are guided by the angle the sun takes at the appropriate seasons to maintain their bearings, while the night-fliers are guided by the constellations of stars and other heavenly bodies.

Tropical Africa is by far the most popular winter resort of numerous migratory birds from Europe and Asia. Large numbers of birds from Central Asia fly regularly to Africa to escape the rigours of winter. While many birds fly to Africa from the Far East, a few from Alaska and Siberia annually travel 7,000 miles up and down between their winter and summer quarters.

The swallow covers 12,000 miles twice a year between North and South America or Europe and South Africa. The Eastern Golden Plover from its nesting grounds in the Arctic regions migrates to Nova Scotia and then south across the Atlantic Ocean over a distance of 1,500 miles to the West Indies and then on to the southern parts of South America. Other golden plovers cross the Pacific to the Hawaiian Islands, South Pacific Islands and to Australia.

The longest known migratory journey of all is undertaken by the Arctic Tern, which for the Arctic winter flies south across the globe to the Antarctic summer and back, covering a distance of 22,000 miles.

It was believed that on migration birds flew at stupendous heights. Although some birds are capable of ascending to higher altitudes it is now known that migratory birds generally fly at heights under 1,300 ft, and still lower over the sea where there are no obstacles. However, when crossing mountain passes they ascend greater heights. For instance, members of an Everest expedition once saw crows and mountain finches (sparrow family) at 23,000 ft and griffon vultures between 20,000 ft and 23,000 ft, while ghoughs (crow family) followed the climbers up to a height of 27,000 ft.

As to the cruising speed of various migrants, scientists have been able to arrive at estimates with the help of radar and speed indicators. Fast-flying species such as ducks and geese maintain a cruising speed of 50-60 m.p.h. under favourable weather. The following are some of the flights on record: coot 160 miles, stork 120 miles (6 hours) woodcock (snipe) 150 to 300 miles, golden plover 2,000 miles and Lathan's snipe 3,000 miles.

Back to Plus