Bird migration7

The word ‘migration’ comes from a Latin word ‘migrare’ which means ‘to travel’.
It is defined as ‘the periodic movement of birds from one place to another to
obtain the advantages of the favourable conditions’
The birds which undergo migration are called ‘migratory birds’ and which will not
undergo migration are called as ‘resident birds’.
Migration means two way journeys
 Journey from home to new place
Back journey from new places to home.

I.KINDS OF AVIAN MIGRATION
1) Latitudinal migration:
From north to south and vice versa e.g.: American golden plover
(Pluvialis), Siberian birds
2) Longitudinal migration:
From east to west
E.g.: Patagonian plover-Falkland island and south Patagonian in sept
and oct for breeding

3). Altitudinal/vertical migration:
movement of birds to high mountains in summer and to low valleys in the winter
E.g.: common wood rock ,Bush chat, Scolopex, Rusticola
4) Partial migrations:
All the birds in a group are not migrating at once. Some will remain at native. Eg : blue
birds ,blue jays of Canada and northern US
5) Erratic migrations/irregular/wandering migration:
migration in all direction in search of food and to avoid enemies e.g.: great blue
herons, cuckoos, warblers, thrushes

6). Seasonal migration:
i) Summer visitors:
some birds visit certain places only in summer and leave in autumn eg:
swifts, swallows, nightingales and cuckoos
ii) Winter visitors:
some birds visit certain places only in autumn and leave in spring to
north e.g.: field fare, snow bunting and red wing
iii) Birds of passage:
some birds stay temporarily in some places on their way of migration e.g.:
snipes and pipers

Besides these some birds also show the following migrations too..They are
A).Climatic migrations:
migrations due to climatic changes that occur daily or
seasonally eg: north- south migration
B).Alimental migration:
migrations that occur due to food and water shortages
C).Gametic migrations:
migrations that aim to occupy some places to carryout reproduction

II. MODES OF MIGRATION
1. Time of migratory flights:
Birds may migrate during day or night. Depending on the time they are
i) Diurnal migrants:
some fly during day time and take rest during night. These birds travel in
flocks e.g.: Robins, Hawks, Cranes, Loons, Pelicans etc..
ii) Nocturnal migrants:
some fly during night time and take rest during day.

2) Range of migrations:
It varies from one/few miles to thousands of miles in different groups but
constant for a particular group.
Himalayan patridges-1 or 2 miles
Chickadees travel about 8000 feet
Golden plovers, sand pipers, boblinks and swallows cover 6000-9000 from
arctic to grassy plains of Argentina
Arctic tern migrates about 11000 miles from the coast of Labrador to
Antarctica.

3) Altitude of flight:
 some birds fly close to the earth.
Routine migration occurs within 3000 feet of the earth.
Small birds have been reported to fly at 5000-14000 feet
altitudes.
Certain avian species even cross the Andes and the
Himalayas at an altitude of 20000 feet or even more

4).Velocity of flight during migration
Cranes, carrions, crows and finches flight with a speed of 30 miles /hr.
Maximum speed recorded of some Indian swift is 176 miles/hr
Birds usually travel 5-6 hours a day, take rest and continue their journey.

5)ROUTES OF MIGRATION:
i. Coastal routes:
Migratory birds usually follow definite routes and is common for going and
returning.
marine birds follow sea routes.
Land birds are known to cross as much as 400 miles of ocean in a single stroke
Large number of migrants follow coastal routes such as
East Atlantic coast line, West Atlantic coastline,
East pacific coast line , west pacific coast line
East indies coast line

ii. River valley routes:
while migrating from planes to hills and from hills to planes migratory birds
cross rivers and river valleys fall in the way.
iii. Mountain ranges:
Very rarely they cross mountain ranges.
the river valleys , which enable them to recognize and remember the routes
and entrances to the countries.

III.ORDER OF MIGRATION
The birds follow a definite order during migration.
Generally adults or old birds start first and the young follow them.
This urge of migration seems to be dependent on the maturity of gonads.
In the return journey young birds start and the adults follow them .
In the migratory order the adult males will be at the forefront ,next comes the
females then young ones and the wounded birds at the end of the flock

IV.PROBLEMS OF MIGRATION
Problem of way finding or navigation:
How the birds are able to find their way?
Land marks :
Experience
Earth’s magnetic field:
YEAGLER & MIDDENDROFT suggested the internal ear reacts to
this
Celestial bodies:
MATTHEUS &SAVER pointed out that the celestial bodies
like sun ,stars help the birds to decide the direction
Home instinct:

V. Causes for avian migration s:
1.Environmental stimuli:
scarcity of food ,decrease of day light
increased cold ,stormy weather, increased pressure etc..
2.Gonadal stimuli:
3.Thyroid hypothesis
4.Antipituitary hormone
5.Metabolic hypothesis

VI.Disadvantages of avian migration
 Migration is expensive in terms of food and energy requirements
 It is dangerous in terms of predation and exposure to climatic
factors. Every year millions of birds die during migration
 Cold weather , snow storms , hurricanes, strong current of wind,
fog, man made light houses , big buildings, television towers are
some of the factors create great problems

VII.ADVANTAGES OF AVIAN MIGRATION
 Survival value
 Better climate
 Longer day light
 Plenty of food
 Increased space for breeding and nesting

VIII.PHYSIOLOGY OF MIGRATION:
 Before migration fat deposition occur for future need of food
reserves And water requirement.
Prior to migration the fat has a physiological advantage over
glycogen as it produce more energy per unit weight and is also
produce more water to cope with high rate of metabolism and
breeding.

Bird migration7

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