Birds, those spectacular and colorful animals, have the characteristic (by the way very enviable) of flying. We have all wondered at some point how do birds manage to fly? Having wings and weighing little allows birds to take flight. The fact that they are light is the result of having a large number of hollows throughout the body: inside the bones, between the viscera, and even in the skin. These hollow sacs are filled with air and connected to the lungs.
However, birds never cease to surprise us, since among them there is a large group that year after year flies thousands of kilometers across countries and even continents, to spend the winter in warmer places and with greater availability of food, this great flight is known as migration.
What is bird migration?
The migratory phenomenon of birds has been known since ancient times and has always caused great admiration in those who have studied it or simply witnessed it. Migration is still not fully understood. Several theories have been issued to explain it, but although they have reasons to be accepted as true, they also have errors that make scientists doubt and, therefore, have been accepted with some reservations.
In general, all theories agree that the annual trip that birds make to other places, allows them to live in two different places, as long as both present more or less favorable conditions to maintain their life. For example, a region has an adequate amount of food and optimum temperature to live, but as it changes as a result of the change of season, the birds move to another site where the conditions are favorable, opposite to those that begin to prevail in the first land. In this new site, they settle until they can return to their place of origin, due to the restoration of the climate and the previous conditions.
In this way, winter migration in birds can be defined as a regular mass movement of the population from their usual summer residence to warmer places in winter. Most commonly, migration takes place in a north-south direction.
Migratory routes in North America
What paths do migratory birds follow to reach their destinations? We now know that migratory birds follow defined trajectories on their journeys known as migratory routes. Migratory routes in North America have been studied for years. The work has consisted of placing numbered hoops on the legs of migratory birds and then recording the birds that are returned by hunters, noting the type of bird, sex, age, and place where it was hunted.
By carefully and patiently collecting data such as the above, it has been possible to determine more or less precisely the migratory routes. It is now known that migratory birds follow definite routes on their journeys to and from their breeding and wintering grounds. The most important migratory flyways in North America are as follows. The Atlantic Flyway, the Mississippi Flyway, the Central Flyway, and the Pacific Flyway.
How do birds orient themselves?
Much research has been done trying to find out what mechanisms birds use to orient themselves during migration. It appears that birds use several sources of information. Some experiments have shown that certain birds are able to be guided by the position of the setting sun, the stars, the direction of winds, the direction of the earth's magnetic field, topographic reliefs, and the activity and cries of other individuals of the same species. However, migratory behavior is becoming increasingly complex and difficult to interpret.
At what speed and altitude is the migration done?
The speed of the migratory flight is usually very high, being between 60 and 110 kilometers per hour (37 and 70 miles per hour). The altitude of the flight can reach up to several thousand meters ( several thousand feet), where the temperature is below zero centigrade. Some birds make, in one go, the entire migratory flight, even if the distance is thousands of kilometers. However, the most common is that the trip is made in stages, flying only during the day and stopping during the night, or vice versa.
Birds of Lake Texcoco
In the particular case of Mexico, more than 100 species of birds migrate to the country every year. That is why Mexico is considered one of the most important wintering areas in the world for them. A striking example is the birds that arrive at the Texcoco and Xochimilco Lakes. Using the central route, year after year thousands of migratory birds from Canada, Alaska, and the United States spend the winter in these lakes.
Migratory birds settle in this area during the fall, winter, and early spring, arriving between 100,000 and 150,000 individuals per year, belonging to 98 species. There are currently protected sites on this lake where migratory species find food and shelter and where resident species breed in increasing numbers.
In 1978, within the Lake Texcoco Commission, the Department of Biotic Resources Management was created, which carried out the first formal work for the conservation of migratory and resident waterbirds. Since then, studies of local movements of migratory populations, habitat studies, feeding habits, and population censuses, among others, have been carried out. Another achievement is the eradication of all hunting in the Federal Zone. Among the migratory groups that arrive at Lake Texcoco are the following.
The most common migratory duck is the mallard duck that comes from Alaska. There are also colorful wintering ducks such as the clown duck, the swallow duck, and the chalcuan duck, among others. Among the resident birds, we find the Mexican duck, a species that was in danger of extinction, and now has found in the Texcoco Lake a suitable habitat for reproduction. Depending on the species, ducks feed on fish, water fleas, fly eggs, dried flies, and crustaceans.
Another important group of migratory birds are the chichicuilotes (Wilson's plover), which are characterized by long beaks and skinny legs. Forty species and around 80,000 individuals arrive at Lake Texcoco.
Two large species, such as the fish egrets, and several small species, such as the heron chapulmera and the so-called water dog, spend the winter in the lakes and grasslands of Texcoco.
Birds of prey
Raptors such as the red-tailed hawk, the white hawk, the peregrine falcon, and a scavenger species such as the red-tailed hawk, the white hawk, the peregrine falcon, and a scavenger species such as the vulture.
Seabirds give us a great surprise when we find them so far from their coasts. Among them are seagulls, cormorants, and even the elegant kingfisher. The enormous white pelicans and brown pelicans winter in the lake, thanks to the abundance of their food, the yellow fish.
Protection and conservation
Birds are an important part of the food web of our planet; they maintain the balance in the terrestrial fauna and prevent the excessive development of other groups such as insects. They are therefore of immense use to humans, who must protect and care for them. However, man is the author of useless and cruel killings. Moreover, agricultural and forestry development has deteriorated the habitat of birds, damaging them more and more. As the situation is alarming, it requires a decisive, timely, and joint intervention which, being a common heritage, involves several countries.
By Citlalli Álvarez