Chordates, Aves Bird migration and flight adaptations

Bird migration

1. BIRD MIGRATION Dr.K.R.SHANMUGAM Department of Zoology PRR&VS Government College Vidavaluru SPSR Nellore- A.P

2. MIGRATION IN BIRDS 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.

3. I.KINDS OF AVIAN MIGRATION 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

4. 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

5. 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

6. 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

7. II. MODES OF MIGRATION 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.

8. 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.

9. 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

10. 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.

11. 5)ROUTES OF MIGRATION: 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

12. i i. 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.

13. 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

14. 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:

15. 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

16. 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

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

18. 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.

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