Come winter seasons, and we see a lot of unusual birds in our surrounding areas. Birds such as wagtails, brown shrikes, pintails, ruddy shelducks, garganey birds, shovellors, mallards, herring gulls are not seen throughout the year because they have come from some parts of the globe for a certain period of time.

These birds are what we called migratory birds. The best place to see such migratory birds are certain wetland or riverine areas. The most striking feature of the migratory birds is that they come in flocks in enormous numbers and often swarmed the areas they visited.

Most of the migratory birds in India come from very far off places in the northern part of the globe, such as the palaerctic regions, across the high mountain ranges of the great Himalayas. Majority of the migratory birds coming to India are ducks, geese and cranes. Migratory ducks fly in an enchanting V-formation; maybe they have to save as much energy as they can because they have to travel a long distance during their migration.

Human beings are always inspired by many behaviors of the birds. The idea just to emulate a flying bird results in the invention of flying machines. Many behaviors of our feathered friends are well studied and well understood and many remain yet to be unraveled.

Bird migration is still a mystery to the scientists.

Questions such as 'Why do birds migrate?' and 'How do birds migrate?' still evade exact explanations. The phenomenon of migration is mostly or always directed from north to south. This idea led some to believe that bird migration is an inheritance of acquired characters.

During Ice age, about 2 billion years ago, the northern hemisphere of the earth was just inhabitable and many birds of the areas migrated towards south in search of more hospitable habitats. Such characters remained acquired and inherited even after the end of Ice age, and bird migrations continue till today.

Birds used many environmental cues for its migration for they have to know 'where to migrate', 'when to migrate' and 'how to migrate'. Photoperiod tells birds when to migrate. Birds start preparation for migration at certain period of particular day length (for example, 8 hours 15minute L).

Just before migration bird usually starts deposition of fats in their body. When this fat deposition reaches certain level, the birds begin to feel restlessness (which is called Zugunrunhe in biological term) and start migrating. The body fats provide energy during the migration. Many migrating ducks fly in an enchanting V-formation, which has a good aerodynamic interpretation or significance in the sense that the ducks by flying in this formation save a lot of energy.

Birds used certain flyway zones for its migration, for example, Indus Valley flyway zone and the Brahmaputra river valley flyway zone in the Indian subcontinent. But some birds fly directly across the high Himalayan Mountains.

Thus it seems that there is no imperation that birds would use one route though the Indus Valley flyway zone is one of the most popular routes among migratory birds coming to India.

In India, bird migration has been studied by the BNHS (Bombay Natural History Society) intermittently since 1980's. So far 4 lakhs birds have been ringed or banded; but the recovery rate was very low (only 1%) and no conclusion on the migration of birds in India can be inferred. Most data on the migration of birds in India comes from many developed countries such as Japan, European countries, the USA, etc.

Recently, one black kite Milvus migrans lineatus ringed in Mongolia in its nest on July 18 2001, by Michael Stubbe from the University of Halle, Germany was captured live near Loktak Lake in Manipur on October 22, 2001. This is perhaps the first concrete evidence of migration of black kite from Mongolia to India and provides the information that black kite is a winter visitor in Manipur, NE India.

Millions of birds annually travel between their nesting sites in the northern hemisphere and their wintering ground in the southern hemisphere. The most amazing aspect of this bird migration is the bird's return to its location faithfully with pinpoint accuracy.

How do they manage to do this? Most birds have remarkable memories and are good at "pattern recognition". Migratory birds usually fly using the position of stars, the sun, and star patterns. Birds also, of course, use landmarks, such as rivers, mountains ranges, coastlines seen during previous journeys as path guides.

But the most important environmental cue the bird used during its migration is the earth's magnetic field. Birds can measure the angle between the magnetic lines that surround the earth and the vertical direction of gravity; and take bearings from this 'magnetic dip'. The value of the magnetic dip at the nesting site is perhaps imprinted in the bird brain.

On its way back home after the winter sojourn, the bird flies in a direction which brings it closer to and ultimately exactly to this figure.

These days, people are talking about the danger of bird flu from these migratory birds, like the recent finding of some carcasses of birds such as red legged falcon in Tamenglong and Senapati districts of Manipur.

It is understandable to think that migratory birds can possibly bring the virus from very far off countries to our state because of their long distance flights. However, we must not go hysterical about these migratory birds (unnecessarily blaming the birds for carrying the virus); though we need to be alerted about the danger being caused by bird flu (because sometimes it can kill people).

Because the danger comes the moment the virus changes to one that can transmit between humans. Then the clock starts ticking. Currently, the WHO puts the danger level at 3 whereas the pandemic level (worldwide epidemic level) is 6.

It has reported from reliable sources that people have handled dead bird without getting sick. Cooking easily killed the virus. Eating cooked chicken or egg is not dangerous. The disease may be transmitted from birds to human, but the danger of infection is quite low.