Grues (Grus grus) al seu pas en migració cap al nord d'Europa, a través dels Pirineus. Al fons, Serra de Guara (2078 m.) Situada enfront de la Foia d'Osca, com a exemple dels alts cims que les aus hauran de travessar / Foto: Jacinto Alduan Palacín - http://jacintoalduan.blogspot.com.es/

Migratory birds: tireless traveler

Do you realize that some birds appear for certain time and place but suddenly, one day, dissapear again until the next year? Where do they go and why do they decide to fly though thousands of kilometres? Certainly, migration of birds is a phenomenon that has fascinated the human being from the beginning. In this post you will have an overview of the migration and discover fun and interesting facts of these wonderful birds. 

WHAT IS THE MIGRATION?

Migration is a natural phenomenon that happens in different species, but is particularly striking in birds. Requirements of essential resources (food, breeding areas,…), in several phases of their life cycle, is the main reason to start the journey to look for more favourable terms. The migration is a regular seasonal  movement that are performed by birds and coincide with the amount of a resource or different seasons, between breeding and wintering grounds.

Migration of short distance, for example when animals are moving from mountain areas at lower altitudes because of the temperature. On the other hand, migration of long distance when birds are traveling thousands of kilometres  through physical, meteorological and ecological barriers.

From Ice Age, migratory birds have evolved to fly long distances because in this way they are able to occupy different habitats and benefit from season resources in other climates. The migratory behaviour originating from an evolution because of climate changes on the Earth, and it is necessary an animal adaptation to the conditions in the new area. This behaviour was developed in species from more Northern latitudes in the Northern Hemisphere and in southern regions in the Southern Hemisphere.

WHAT TYPES OF MIGRATORY MOVEMENTS ARE THERE?

Migratory birds travel twice per year, in different seasons and times in their annual cycle. In the prenupcial (or spring) migration period birds fly from wintering to breeding areas. In the breeding areas there are enough resources to feed their offspring and safe breeding places. In the postnupcial (or winter) migration period adults and young birds fly to the wintering areas because of the weather and the high resource availability.

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Group of grus in the wintering area where weather and conditions are better than en North of Europe – Photo: Manuel Gómez Calzado

These movements have concrete patterns in each species and develop the different migratory routes, but researches have discovered the routes can be variables.

So, according to the migratory pattern there are longitudinal, altitudinal or latitudinal migrations. It could be variances in migratory behaviour between individuals, including in the same species, according to several factors us age, sex or population.

MIGRATORY ROUTES

Birds use these migratory movements through specific routes, with important features (catchment of a river, mountain ranges, coast,…) and ensure favourable conditions for the journey. Also, the rest areas are used to rest and feed in long routes.

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Migratory routes on the world – Photo: SEO-BirdLife

In the majority of birds from Europe and Asia, such us storks and vultures, spend the winter in the tropical Africa area, crossing their route the Arabian Peninsula and the Suez Canal. Migratory birds from the United States and Canada have their wintering areas in Mexico and Central America, and their routes depend of their area of origin: birds from east cross through the Gulf of Mexico or the Mississippi river basin; birds from west through the Rocky Mountains and Mexico Mountains, and finally, birds from Pacific used the cost or the open sea.

However, the routes can be different and depend of the distribution of birds; for example a bird species from Eurasia that pervaded North America. Their relatives used to spend the winter in Africa, so the population from North America cross Canada, the North Atlantic and Europe to spend the winter in Africa.

Researches show the routes are not so fixed us we though, and they can change according to the requirements of the species and environmental conditions over time. Also, there are fluctuations between different groups in the same species.

HOW DOES MIGRATION HAPPEN?

Human beings have always tried to answer the question ‘how is it possible birds fly so far?’. Several researches shows birds use a mix of mechanisms to migrate: the
Earth’s magnetic field, positions of the Sun, Moon and stars, polarized and ultraviolet light, recognising geographical features, reflected sound waves, taste and smell.

A research showed the migratory birds have proteins on their retina that is like a light-sensitive compass. When it is lightened with sunset light, the CPF molecule reacts and forms other compound that is sensitive to the magnitude and direction of a weak magnetic field. Two electrons rotate in opposite direction because of this chemical reaction, and the bird finds the north and south direction.

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A group of proteins that birds use during the migration – Photo: http://concienciangela.blogspot.com.es/

For some birds, such us the mayority of passerine birds, migration is an innate and individual process and they have special mechanisms to find the right way. In other cases, when birds fly in group, the migratory behaviour is developed through social learning because young birds travel with adults. Birds born of parents with different migratory routes used to choose a middle migratory route.

DISCOVERING SOME CURIOUS FACTS

The bird that travel father is the Arctic tern (Sterna paradisaea) from the Arctic, its breeding area in summer, to Antarctic to find food in winter. This distance is about 80000 km per year, and this species has developed the ability to sleep with a hemisphere off and another on flying directly.

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Arctic stern (Sterna parasidaea) and its migration – Photo: Birdlife

 

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In a research about Alpine swift (Tachymarptis melba), it was showed that this species can stand on the air for 6 months in their migration to Africa. The most interesting is that all vital processes are being on the air.

The migratory bird that flies higher is the common crane (Grus grus) and they can fly over the Himalaya mountain each year carried by the thermal currents. Breeding areas of this species are in the north of Europe and Centre and Northwest of Asia, also there are some groups in southeastern Europe and close to the Caspian and Black Seas. The wintering areas are in Spain, Portugal, north and east of Africa, south of France and south Asia.

REFERENCES

  • “Birds Migratory flyways influence the phylogeography of the invasive brine shrimp Artemia frasciscana in its native American range” – Joaquín Muñoz, Franciasco Amat, Andy J. Green, Jordi Figuerola and Africa Gómez
  • Effect of climate on the migration behavior of the common buzzard Buteo buteo – Martin, Beatriz; Onrubia, Alejandro; Ferrer, Miguel – 2014, Climate Research 60: 187 – 197 (2014)
  • Regional Forest Fragmentation and the Nesting Success of Migratory Birds – Robinson, Scott K.; Thompson III, Frank R.; Donovan, Therese M.; Whitehead, Donald R.; Faaborg, John; – Scientific Journal (JRNL) – 1995

 

 

 

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