Birds always migrate to an environment suitable for their lives. How do they judge the climate?

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Generally speaking, there are four points:

1, training and memory, genetics determines that young birds have the habit of following old birds in groups and obeying their instructions.

2. Ground visual orientation

3. Celestial navigation

4, magnetic orientation!

Migration, Orientation and Navigation of Birds

Bird migration refers to the large-scale, regular, extensive and seasonal movement of bird population between its summer breeding area and wintering area. The basic characteristics of this movement are periodicity and orientation, and it is often carried out in large groups. People are generally concerned about the following questions: ① How do birds migrate and what are the reasons for migration? (2) How did bird migration originate? ③ How do birds orient during migration? In recent years, due to the application of many modern experimental techniques, the research on bird migration's behavior and directional navigation mechanism has been deepened and achieved initial results.

I. bird migration and its causes

The current research results show that many birds migrate seasonally. Of the 589 species of birds that breed on land in Palaearctic realm, 40% species, with a total of about 5 billion birds, fly south to Zhaodong every year, not including the birds that migrate in this area. There are 160 species of passerine birds bred in Canada, among which 120 species migrate, accounting for 75%.

Birds often migrate in a certain formation along a certain route. The distance of migration is near and far, from several kilometers to tens of thousands of kilometers. The longest journey is the Arctic tern, as far as1.8000 km. This bird breeds in the Arctic, but flies to the Antarctic coast for the winter. In the process of migration, birds generally don't fly too high, only a few hundred meters, and only a few birds can fly over Mount Everest. When moving, the flight speed is 40 ~ 50 km/h and the continuous flight time can reach 40 ~ 70 hours. & lt/P & gt；

Many birds must store enough energy before migration. This is an adaptation to a long flight. The main way to store energy is to deposit fat. Fat not only provides energy for migratory birds, but also the water produced during fat metabolism can be used by the body. By storing fat, many birds greatly increase their weight and even double it. For example, the black-capped white-cheeked warbler in North America and the water reed warbler in Europe generally weigh about 1 1 g, but before migration, they can reach about 22 g, and the deposited fat can be used for their flight 100 hours. & lt/P & gt；

Bird migration's reasons are very complicated. It is generally believed that the migration of birds is an adaptive behavior to the periodic changes of environmental factors. Seasonal climate change is the main reason for migratory birds' migration. Due to climate change, food shortages often occur in the cold winter and tropical dry season in the north, which forces some individuals in the bird population to migrate to other food-rich areas. This behavior was finally fixed by the power of natural selection and became an instinct of birds. & lt/P & gt；

Migration brings many benefits to birds, mainly in:

(1) makes birds always live in the most suitable climate, and has a variety of food sources, which is conducive to maintaining their vigorous metabolism;

Migration can also create the most suitable conditions for raising offspring, because raising offspring requires a lot of food;

(3) The north can hatch the most eggs, with a long season and abundant insects, so the parent birds can have the opportunity to fully collect food;

(4) There are few enemies in the north, and the appearance of this annual fragile juvenile black will not promote the formation of enemy population;

⑤ Migration can greatly expand the activity space, which is conducive to reproduction and occupation;

⑥ It is beneficial to automatic balance and can avoid climate disparity;

⑦ Migration provides opportunities for birds to spread to new distribution areas, and also provides opportunities for different individuals to contact and mate, so it is also of great significance in evolution. & lt/P & gt；

Many birds are born and can be learned. Harris's experiment of changing parents can prove this point. He exchanged the eggs of silver gulls and black-backed gulls, so he got 900 young birds raised by his upright relatives. The results of ring records of these young birds show that; The silver gull flew to France and Spain with its adoptive parents, while the black-backed gull moved to its wintering place on the European continent like its biological parents, although its adoptive parents stayed in Britain for the winter. & lt/P & gt；

The migration behavior of birds is also produced in this process. Because the environment is constantly changing, nature has always been in the process of development and change. Even today, migration behavior still forms and disappears among these birds. For example, the wild canary was once a resident bird in the Mediterranean. In the past few decades, the distribution area has expanded to the Baltic region of continental Europe. Now this bird is still a resident in the Mediterranean, but it has become a migratory bird in the new distribution area. & lt/P & gt；

Second, the origin of bird migration

There are three different views on the origin of bird migration:

Birds originated in the south. As the continental plate drifted from south to north, many birds were brought to the north, so they tried to return to their hometown in the south and formed the habit of bird migration.

(2) Birds originated in high latitudes, and the invasion of Quaternary glaciers from north to south forced birds to migrate to the south. When the glaciers retreated in summer, birds could regularly move back and forth between breeding grounds and wintering grounds, thus forming migration behavior;

(3) Birds originated from tropical forests in the south, and a large number of population reproduction caused an increase in food demand. Therefore, ecological pressure causes some birds to spread to the places where glaciers retreat to the north in summer. When glaciers come and go back to the south for the winter, over time, they form regular migration behavior. Comparatively speaking, the first view is somewhat doubtful. Because modern geological research shows that the obvious continental plate movement was completed long before the appearance of birds. Both the second view and the third view have some evidence. But the third view is more in line with modern ecological thought and seems more reasonable. & lt/P & gt；

Thirdly, the directional navigation mechanism of birds.

The most striking feature of migration is that each species has a fixed breeding area and wintering area. Therefore, migrating birds must know where they are, where they are going, the route and direction of their destination, that is, birds must have the ability of directional navigation during migration. Birds not only have the ability of directional navigation, but also are quite developed. Experiments show that many birds (such as swallow and penguin) can return to their original nests to breed in the next spring. That is, migratory birds are transported by plane to areas far away from the migration route, and they can still return to their original habitat after a few days of release. Therefore, people have long understood the phenomenon of directional navigation of birds. However, the research on navigation and positioning mechanism didn't begin until 1950s. Through experiments, people put forward many theories to explain the bird orientation mechanism, including the following points:

1. Training and memory.

It is believed that birds are born with a sense of direction determined by heredity. This sense of direction, as young birds migrate with their parents, constantly strengthens their memory of the migration route. & lt/P & gt；

2. Visual orientation

Relying on the topography of mountain, coast, river, forest, desert and other settlements and migration routes as markers, we will continue to learn from the old birds about the traditional migration network. For example, Han Jian birds were transported to more than 300 kilometers by hand and released. These birds must first try to find the familiar Atlantic coastline and then fly back to their original habitat quickly. Although the characteristics of land may not be very important to birds that migrate at night, there are still some birds that can determine their position and adjust their flight direction according to the signs of land. & lt/P & gt；

3. Celestial navigation

Birds can use the positions of the sun and stars to determine their own position. Stars are especially important for birds that migrate at night. As for the experiment of sun positioning, Kramer's research on purple-winged birds provides evidence for this view. He put the migrating myna in a cage with windows on all sides and treated it with hormones to make it into a migratory state. So it can be seen that the herbivorous bird flaps its wings in a certain direction (that is, its migration direction), and this flapping behavior will not appear on cloudy days. When a mirror is used instead of the orientation of the sun, the direction of its wings can be changed in a predetermined direction. Therefore, he believes that the migration of carnivorous birds depends on the position of the sun. The research on penguins and shrike also shows that the sun orientation mechanism exists. Regarding the orientation of the stars, Sol first experimented with the European reed warbler in a round cage. Prove that these birds can be oriented according to the position of stars in the night sky. Since then, a lot of experiments have been done. By changing the position of artificial stars, birds can also change their migration direction in a predetermined direction, just like the above experiments. Now it is known that birds that can use stars to locate themselves include diphtheria finches. & lt/P & gt；

4. Magnetic orientation

This is a way for birds to determine their direction by sensing the polarity of the earth's magnetic field. A long time ago, people speculated that the navigation position in the bird migration process might be related to the magnetic field. Experiments in recent years have confirmed the existence of geomagnetic field orientation mechanism. When an artificial magnet with a specific polarity is added to the head of the homing pigeon, the homing pigeon can't fly correctly and can return to its nest normally even on a cloudy day without magnetic field. In addition, bird migration can also rely on wind direction, smell orientation and so on.

In a word, the migration of birds is a very spectacular and wonderful behavior. The directional navigation mechanism in the process of migration may be the most complicated problem in ornithology. Although great progress has been made in the study of migratory behavior and orientation mechanism, more and more in-depth research work is needed to solve the mystery of migratory birds' migration.