Bird’s Migration: What, Why, When and where?

Approximately 10,000 species of birds are known on Earth. Slightly less than half are migratory. A total of about 4,000 species of birds migrate back and forth between their breeding and wintering grounds. About two-thirds of them travel long distances, flying up to 20,000 kilometres a year.

And there are even more impressive figures. The cuckoo, for example, moves for about eight months of the year. Swallows fly up to 1,000 kilometres a day, and storks save up to 90 per cent of their energy in gliding flight.

Annual migration

Every year during the months of September, October and part of November, millions of resident birds of the Arctic, when the winter that freezes the waters and when the snow falls abundantly that covers the entire ground, leaves them without food, so they start the flight to other geographical places in the world where they can survive.

This displacement of birds is what is known as migration and that is why they acquire the name of migratory birds. They do so by genetic instinct, triggered by a primary physiological stimulus due to the change in day length and also related to hormonal changes.

How many Bird migrate each year

It is estimated that in the world there are 20,000 million migratory birds belonging to 10,000 species of which 50 per cent migrate. Migration is primarily a Northern Hemisphere (Arctic) phenomenon. In the southern hemisphere (Antarctica), seasonal migration is less evident.

From the Arctic, they begin a flight that takes them to different continents: Europe, Asia, Africa, Australia, America and consequently to the most diverse countries: Canada, the United States, Central and South America, Italy, India, Pakistan, France, Russia, China, Indonesia, Thailand, among others. Others, in short, are distributed throughout the world depending on the species and the habitat they require.

Wherever they arrive, they remain for a period of six months, feeding well to begin the return trip to the Arctic between the months of February, March and April,  to complete the biological cycle of laying, breeding and rearing.

Why migratory birds?

Avian migration is a natural miracle. Migratory birds fly hundreds and thousands of kilometres to find the best ecological conditions and habitats to feed, reproduce, and raise their young. When conditions at breeding sites become unfavourable, it's time to fly to regions where conditions are better.

Birds often follow established migratory routes, generally north-south routes with good places to rest and recharge along the way. Several species of birds share these routes and must cope with bad weather, dehydration, hunger and predators.

There are many different migration patterns. Most birds migrate from northern breeding areas to southern wintering grounds. However, some birds breed in southern Africa and migrate to northern wintering grounds, or horizontally, to enjoy milder coastal climates in winter. Other birds reside in lowlands during the winter months and climb a mountain during the summer.

How do they know it's time to go?

In some birds, changes in environmental conditions, such as day length, cause hormonal stimulation that suggests it is "time to fly." Birds' internal biological clocks can also detect the change of season, through changes in light and possibly air temperature.

Once the birds go into migration mode, they overfeed. So they build up reserves to cope with the journeys, says Lucy Hawkes, a migration scientist at the University of Exeter in the UK who currently tracks Arctic terns.

“Somehow, the birds realize that they will soon have to migrate and start to fill up the fuel tank,” says Hawkes. Local and regional weather conditions, such as rain, wind and air temperature, can also determine when migratory birds take flight.

Do Indian birds migrate?

Yes, the species is called a "local migrant" - they fly within Indian borders. During the summers, they breed in the central and northern parts of India while migrating south in the winter.

Which country records highest number of migratory birds

The table below will give you an idea of the approximate number of species of migratory birds in each nation and territory.

Country	Number of Migratory birds species
China (mainland)	601
USA	573
Mexico	517
India	470
Argentina	448
Canada	447
Russia (Asian)	445
Brazil	395
Iran, Islamic Republic of	375
Kazakhstan	360
Colombia	360
Japan	359
Pakistan	357
Peru	355
Myanmar	354
Russia (European)	348
Nepal	344
Thailand	339
Bolivia	333
Russia (Central Asian)	329
Vietnam	328
Turkey	327
Israel	317
South Korea	316
Turkmenistan	315
Guatemala	313
Iraq	312
Costa Rica	311
Sudan	306
Spain	306
Egypt	300
Azerbaijan	300
France	299
Mongolia	298
Uzbekistan	298
Italy	296
Afghanistan	295
Chile	295
Venezuela	294
Greece	293
Syria	289
Paraguay	288
Bulgaria	287
Saudi Arabia	287
Ecuador	286
Honduras	283
North Korea	279
Romania	279
Kenya	278
Bangladesh	278

Change of routes

The biggest threat facing birds today is climate change, which is causing radical changes in their migratory behaviour, breaking natural orders carefully passed down from generation to generation for thousands of years, so it is believed that species will have to adapt, move or disappear.

Traditionally, they arrived in each nation by specific geographic routes, which are being modified, getting lost and reappearing outside their normal distribution area, even for hundreds of kilometres, due to various natural, climatic, and environmental phenomena.

Interesting facts

• Hummingbirds are the smallest migrating bird

• Migrating birds can travel VERY far

• Some birds migrate at high altitudes

• Migrating birds know where to go

• Birds prepare for migration

• Birds migrate at different times

• Wisconsin is a popular migratory destination state

• Migrating birds face many threats during their journey

• Neotropic birds are a type of migratory bird

• Birds need specific items when landing in yards after migration.

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