Bird migration, Types of birds, Advantage and disadvantage of birds, their cause

1. Shri Shankaracharya Mahavidyalaya, Junwani , Bhilai
Bird Migration
Dr. Sonia Bajaj
(Head of Department)

2. Bird Migration
The word “migration” has come from the Latin word migrara which means going from
one place to another. Many birds have the inherent quality to move from one place to
another to obtain the advantages of the favorable condition.
Bird migration is a two-way journey from breeding or resting place to feeding or nesting
place and vice versa. It is a periodic, regular, to and fro movement. Birds are the
greatest migrants.
migration means two-way journeys—onward journey from the ‘home’ to the ‘new’
places and back journey from the ‘new’ places to the ‘home’. This movement occurs
during the particular period of the year and the birds usually follow the same route.
There is a sort of ‘internal biological clock’ which regulates the phenomenon.
Definition:
According to L. Thomson (1926), bird migration may be described as “changes of habitat
periodically recurring and alternating in direction, which tend to secure optimum
environmental conditions at all times”.
Bird migration is a more or less regular, extensive movements between their breeding
regions and their wintering regions.

3. Types of Bird Migration
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,
(v) Total,
(vi) Vagrant or Irregular,
(vii) Seasonal,
(viii) Diurnal and
(ix) Nocturnal.

4. (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.
Ex- Cuckoo breeds in India and spends the summer at South-east Africa and thus covers
a distance of about 7250 km.
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.

5. (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.
(iii) Altitudinal migration
The altitudinal migration occurs in mountainous regions. Many birds inhabiting the
mountain peaks migrate to low lands during winter. Birds migrate either in flocks or in pairs.
Swallows and storks migrate a distance of 9650 km from northern Europe to South Africa.
Golden plover(American),Ruff breeds at Siberia and travels to Great Britain, Africa, India and
Ceylon thus travelling a distance of 9650 kilometers.

6. (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.

7. (vi) Vagrant(aavaara) 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.
Herons, black strok (Ciconia nigra),Spotted eagle( Aquila clanga).
(vii) Daily migration
Some birds make daily journey from their nests by the influence of environmental factors
such as temperature, light, and humidity also.
Crows, herons and starlings.

8. (viii) Seasonal migration
Some birds migrate at different seasons of the year for food or breeding, called seasonal
migration.
cuckoos, swifts & swallows
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.
(i) Diurnal (Daily) migration-Many larger birds like crows, sparrow, 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.

9. Characteristics of migration
1. Speed-During migration most of the birds fly at their normal speeds which varies
for different bird’s .the crows and cranes etc. fly at a speed of about 50 kilometer
per hour. The ducks fly at 65 to 75 kilometer per hour. The speed of migration also
depends on the direction and speed of the wind.
2. Migratory birds often fly at night .the day flying birds fly at such a height that they
are not easily seen.
3. Ordinarily birds fly at a height above below 1000metres.
4. The ducks and crane fly in definite rows.
5. During migration, the bird rest in the way for one or two hours.
6. The migratory birds fly every year along same route and after reaching their
destination return to their old habitats. Sometime, they even find out their old nests.

10. Causes of Migration
1. Gonadal changes-It is widely accepted that the impulse to migrate in birds is possibly
instinctive and the migration towards the breeding grounds is associated with gonadal
changes.
2. Environmental stimuli-the sunlight and air act as stimulants for migration. The deficiency
of food, short day, reduction of the heat in sunlight increase in cold and stormy weather etc.
also stimulate the bird to fly towards the safe and suitable environments.
3. Metabolic aspects-Due to the change in the metabolic activities the accumulation of facts
starts which induce the migration.
4. Thyroid hypothesis -the hormones secreted by the thyroid regulate the metabolism
therefore it also controls the migration.
5. pituitary hormone-This hormone regulate migration and tendency for migration.

11. Significance of Migration
Advantages of Bird Migration
1. The birds get suitable place for breeding.
2. As a result of migration, the birds escape cold and stormy weather for excessive heat.
3. The birds get abundant food supply in the place of migration.
4. As a result of arrival at one place from cold place, the birds get longer day time to
search their food.

12. Disadvantages of Bird Migration
1. Many young’s are not, able to reach the destination because they die during
the course of the continuous and tiresome journey.
2. Sudden changes in the climate such as storms and hurricanes, strong current of
wind, many migratory birds get killed.
3. Sometimes man-made high tours, telegraph wires and light houses cause the
death of migratory birds.
4. Man they are responsible for the death of the migrants. They shoot at these
poor birds just for their own leisure and amusement.
5. Small and helpless birds are destroyed by their enemies.

13. References-
Modern text book – R.L.Kotpal
Jantu Vigyan- S.M. sexsena
Jantu Vigyan- Dr.H.N. Baijal