Question

Migratory routes of birds with description.

Answer 1

Explanation:

All birds do not migrate, but all species are subject to periodical movements of vary­ing extent. The birds which live in northern part of the hemisphere have greatest migra­tory power.

Migration may be:

(i) Latitudinal,

(ii) Longitudinal,

(iii) Altitudinal or Vertical,

(iv) Partial,

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(v) Total,

(vi) Vagrant or Irregular,

(vii) Seasonal,

(viii) Diurnal and

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(ix) Noctur­nal.

(i) Latitudinal migration:

The latitudinal migration usually means the movement from north to south, and vice versa. Most birds live in the land masses of the northern temperate and subarctic zones where they get facilities for nesting and feeding during summer. They move towards south during winter.

An opposite but lesser movement also occurs in the southern hemisphere when the seasons are changed. Cuckoo breeds in India and spends the summer at South-east Africa and thus covers a distance of about 7250 km.

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Some tropical birds migrate during rainy season to the outer tropics to breed and return to the central tropics in dry season. Many marine birds also make considerable migra­tion. Puffinus (Great shearwater) breeds on small islands and migrates as far as Greenland in May and returns after few months.

It covers a distance of 1300 km. Penguins migrate by swimming and cover a considerable distance of few hundred miles. Sterna paradisaea (Arctic tern) breeds in the northern temperate region and migrates to the Antarctic zone along the Atlantic. It was observed that Sterna covers a distance of 22 500 km during migration!

(ii) Longitudinal migration:

The longitudinal migration occurs when the birds migrate from east to west and vice- versa. Starlings (Sturnus vulgaris), a resident of east Europe and west Asia migrate towards the Atlantic coast. California gulls, a resident and breed in Utah, migrate westward to winter in the Pacific coast.

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(iii) Altitudinal migration:

The altitudinal migration occurs in moun­tainous regions. Many birds inhabiting the mountain peaks migrate to low lands during winter. Golden plover (Pluvialis) starts from Arctic tundra and goes up to the plains of Argentina covering a distance of 11 250 km (Fig. 9.54).

Birds migrate either in flocks or in pairs. Swallows and storks migrate a distance of 9650 km from northern Europe to South Africa. Ruff breeds at Siberia and travels to Great Britain, Africa, India and Ceylon thus travelling a distance of 9650 kilometers.

(iv) Partial migration:

All the members of a group of birds do not take part in migration. Only several members of a group take part in migration. Blue Jays of Canada and northern part of United States travel southwards to blend with the sedentary populations of the Southern States of U.S.A. Coots and spoon bills (Platalea) of our country may be example of partial migration.

(v) Total migration:

When all the members of a species take part in the migration, it is called total migration.

(vi) Vagrant or irregular migration:

When some of the birds disperse to a short or long distance for safety and food, it is called vagrant or irregular migration. Herons may be the example of vagrant or irregular migration. Other examples are black stork (Ciconia nigra), Glossy ibis (Plegadis falcinellus), spotted eagle (Aquila clanga), and bee eater (Merops apiaster).

(vii) Daily migration:

Some birds make daily journey from their nests by the influence of environmental factors such as temperature, light, and humidity also. Examples are crows, herons and starlings.

(viii) Seasonal migration:

Some birds migrates at different seasons of the year for food or breeding, called seasonal migration, e.g., cuckoos, swifts, swallows etc. They migrate from the south to the north during summer. These birds are called summer visitors. Again there are some birds like snow bunting, red wing, shore lark, grey plover etc. which migrate from north to south during winter. They are called winter visitors.

Nocturnal and Diurnal Flight:

(i) Diurnal migration:

Many larger birds like crows, robins, swal­lows, hawks, jays, blue birds, pelicans, cranes, geese, etc. migrate during daytime for food.

These birds are called diurnal birds and gene­rally migrate in flocks.

(ii) Nocturnal birds:

Some small-sized birds of passerine groups like sparrows, warblers, etc. migrate in darkness, called nocturnal birds. The darkness of the night gives them protection from their enemies.