Some invertebrates, such as oriental migratory locust and butterfly; Reptiles, such as turtles; Mammals such as bats, whales, seals, deer, etc. And some fish have seasonal long-distance residence changes. The migration of animals is regular and directional, mostly in large groups.
The migration of birds occurs periodically between the breeding area and the wintering area every year, mostly between the northern and southern hemispheres and a few between the eastern and western hemispheres. People divide birds into migratory birds and resident birds according to the activities in bird migration. Resident birds stay in their birthplace all the year round and do not migrate, such as sparrows and magpies. Among migratory birds, birds that fly to breed in summer and fly to the south in winter are called summer migratory birds, such as family swallow and cuckoo. Birds that fly in winter and breed in the north in spring are called winter migratory birds, such as some wild ducks and geese.
There is a proper term for fish migration called "migration". Most fish can be said to be migratory fish, and only a few fish do not show regular migration. Fish migration can be divided into three types according to the purpose: reproductive migration, feeding migration and wintering migration. Black carp, grass carp, silver carp, bighead carp, yellow croaker and salmon all migrate.
Large-scale migration of mammals, such as reindeer across the snow. Every winter, thousands of reindeer gather in a huge group and move from north to south to the edge of the forest permafrost zone. The following spring, they set out for the northern coast of the Arctic Ocean. In April and May, these deer arrived at a secluded place on the tundra they were familiar with, where they raised their children.
The migration of insects can sometimes work miracles. The most famous is Butterfly Jun, which is produced in America. They flew from Central America to Canada in spring and returned to Central America in autumn, with a journey of 45,000 kilometers, which lasted for several months. It's really amazing.
Animal migration behavior is an adaptive phenomenon. With this activity, the environmental conditions they need in a specific life period can be met, and the survival of individuals and the prosperity of races can be reliably guaranteed.
The migration of birds
Bird migration refers to the long-distance round-trip migration of some species of birds between breeding grounds and wintering grounds in spring and autumn every year. These migratory birds are migratory birds, or migratory birds. The migration of migratory birds has certain periodicity, directionality, routinization and regionality.
Studying the migration behavior of birds, knowing the migration time and route, migration quantity, population relationship, homing ability, mortality rate, survival rate and life span, as well as the relationship with the environment of breeding and wintering areas, can provide scientific basis for protecting rare and endangered birds, using migratory birds to protect agricultural and forestry production and maintain ecological balance, ensuring aviation safety, planning and utilizing economic migratory birds, preventing the spread of epidemics, and formulating laws, which will bring great society to mankind.
Classification of birds according to their migration or living habits.
Birds can be divided into resident birds, migratory birds, drifting birds and lost birds according to whether they migrate or not.
(1) residents
Birds that stay in their habitat all the year round are collectively called resident birds. Resident birds usually live in the same area all the year round, or only migrate short distances along the hillside.
(2) Migratory birds (migratory birds)
Refers to the birds that regularly migrate long distances between breeding grounds and wintering grounds along a relatively stable migration route with the change of seasons in a year. Migratory birds usually migrate twice a year, once in spring and once in autumn. In spring, most migratory birds fly from the south to the north and from the wintering area to the breeding area. Autumn migration is mostly from north to south, from breeding ground to wintering ground, but almost no bird flies directly from its breeding ground to wintering ground, and it has to stop at suitable sites many times. The annual migration time of various birds rarely changes. The way of migration is also fixed all year round, and it often flies along certain terrain, such as rivers, coastlines or mountains. Many birds that migrate to the south and the north follow the same path. Bird migration's way is different. Goose, crane and other large bird migration often gather in groups to form a "zigzag" or "herringbone" team; Smaller birds, such as Ruyan, form a sparse flock; Raptors often fly alone, and individuals always keep a certain distance. Birds mostly migrate at night to avoid the attack of natural enemies, especially insect-eating birds, while raptors mostly migrate during the day.
1: Summer migratory birds are a kind of migratory birds, which breed in a certain area in summer, fly to warmer areas in the south in autumn, and return to this area to breed in the following spring. As far as this area is concerned, it is called summer migratory birds.
2. Birds who stay in winter and spend the winter in a certain area, fly to the north to breed in the following spring, and fly to the area for the winter in autumn. As far as this area is concerned, it is called winter migration.
3. Travellers or migratory birds do not breed or overwinter in a certain area when migrating. These species are called travelers in this area.
Therefore, the same bird is a summer migratory bird in one area and a winter migratory bird in another area.
(3) stragglers
In the process of migration, birds that deviate from the usual migration route or habitat and occasionally go to different places due to strong winds or great changes in other climatic conditions.
(4) Stray birds
Roaming, also known as wandering or hunting, is an irregular activity. Vagrancy seems to be mainly caused by fluctuations in external food conditions. Hunting activities are mostly limited to some raptors and marine birds.
The rhythm of bird migration
Bird migration's behavior has obvious rhythm.
(A) bird migration's circadian rhythm
Bird migration is a long and dangerous journey. The long-term natural and historical changes have caused the migratory birds to have periodic physiological changes every year, and the nerve regulation and energy storage have rhythmic changes.
1, the energy storage rhythm before bird migration.
The energy consumption in bird migration depends entirely on the energy stored in the body in the form of fat. Therefore, birds should accumulate fat before migration to ensure energy consumption during migration. Migrating birds flying over deserts and oceans need to store more fat, because they can't get food on the way and have to complete the whole migration constantly. Most other migratory birds can land in suitable places to feed and quickly re-accumulate lost fat in order to continue their journey.
2. Rhythm changes of bird migration's pre-neuroendocrine.
Bird migration's activities are controlled by neuroendocrine system. With the extension of sunshine, the pituitary gland secretes corticosterone and prolactin through the action of pineal gland. The combined action of these two hormones enables birds to complete a series of physiological preparations, including gonad development, fat accumulation and the enhancement of directional ability.
(2) bird migration's time law.
1, annual rhythm of bird migration.
Bird migration usually migrates from wintering place to nesting place in spring and from nesting place to wintering place in autumn. The migration date varies from species to species and is also restricted by environmental factors (nutrition, etc.). The date of moving into the nesting site is related to the arrival of good ecological conditions, and the date of moving in and out of each bird is also different. Generally speaking, birds that move to nesting sites early in spring move out early, and birds that move later move out late.
2. The daily rhythm of bird migration.
During their stay in bird migration, different kinds of birds not only changed their annual rhythms, but also changed every day. Generally speaking, there are different types of migration, such as day migration, night migration and day and night migration. All types of migration have the changing rules of start time, climax time and end time. Insect-eating bird migration spends most of its time at night, while raptors mostly migrate during the day.
(3) Gender and age rhythm in bird migration.
Birds have different migration rhythms not only among different species, but also among birds of the same age or sex. In bird migration, not the same bird flies back or away from its birthplace at the same time. First, the "vanguard troops" fly first. After a period of time, the main group (basic group) began to move, and finally the latecomers (or stragglers). The number distribution of these three groups of birds varies with species and years. In some years, most birds arrive immediately after the "vanguard", while others arrive much later.
(d) The relationship between bird migration rhythm and migration distance and climate.
Due to the difference of bird's body shape, food characteristics and migration distance, the order of various bird migration is also different. The observation shows that the migration sequence of various birds is not obvious in the northward migration in spring, but in the southward migration in autumn, small birds generally move south first, and large birds finally move south. Birds that migrate long distances begin to migrate in early spring, but return in late autumn. When birds begin to migrate is restricted by many factors, including their internal physiological preparation and external environmental conditions (such as sunshine length, temperature, rainfall, etc.). Generally speaking, weather factors play an important role.
Bird migration route and migration form, as well as the distance, speed and height of migration.
(A) bird migration's route
The migration route of birds refers to the place where they pass from wintering ground to nesting ground. The migration route of birds is the result of natural selection, which is mainly formed by the adaptive choice of birds to natural climate, geographical obstacles and natural environment. Generally, on the migration map, the position of the ring and the position of the ring are connected by a straight line, and this line becomes a theoretical or ideal migration route. In fact, no bird flies in a straight line, which is mainly caused by many factors such as ground structure, landscape type, vegetation, food, weather and so on.
(B) the form of bird migration
There are various forms of bird migration. According to the migration of birds between two areas, the width of flight path can be divided into two forms: wide migration and narrow migration. No matter what kind of birds live in a wider area, the long-distance route is very close. Compared with the area of this area, the migration path is like a road. In this case, migration is called narrow edge migration. On the other hand, if the migration path is not like a road compared with the residential area, this form of migration is called wide-area migration.
For example, birds in migratory groups can be divided into simple types and mixed types. It has been observed that people who migrate north in mixed groups or single groups in spring are often original groups when they migrate south in autumn.
As far as migration areas are concerned, in the same population, there are both parallel migration in the same direction (that is, group A moves to A 1 wintering ground and group B moves to B 1 wintering ground) and cross migration (that is, group A moves to B 1 wintering ground and group B moves to A 1 wintering ground).
(3) The distance, speed and height of bird migration.
The distance between the breeding ground of migratory birds and the wintering ground can range from several hundred kilometers to tens of thousands of kilometers.
Bird migration speed refers to the average speed of migratory birds in the whole migration process. The speed of land migratory birds is mostly 30-70 kilometers per hour, and birds fly for 6-8 hours per day, 30-40 kilometers per hour, with an average of 200-280 kilometers per day. Through observation, it is found that the migration speed of migratory birds is influenced by wind (airflow), which is fast with the wind, slow with the wind, and also affected by temperature (cold and slow; Hot block) and season (spring is fast; Autumn is slow). Therefore, many bird migration migrate by wind (airflow) during the daytime (because there is strong updraft activity on the mainland) or during the monsoon season. This is particularly evident in the migration of raptors, who often roll forward in groups by hovering and gliding.
The height of bird migration is generally lower than 1000m, the migration height of small songbirds is lower than 300m, the height of large bird migration can reach 3000~6300m, individual species can fly over 9000m, and the migration height of birds at night is often lower than during the day. The migration height of migratory birds is also related to the weather. When the weather is clear, birds fly higher; When there are clouds or strong headwinds, it will drop to low altitude.
Migration Path and Direction of Birds (Navigation)
Although the migration routes of migratory birds are different, most of them are in the north-south direction, and they migrate seasonally between the northern and southern hemispheres (some species migrate short distances, limited to the northern hemisphere, and some species may migrate east-west, or northeast and southeast). There are three bird migration Continental Bridges in the world, or "North-South Continental Bridges". These three continental bridges are: North America-South America, Europe-Africa and Asia-Oceania.
(A) the migration path of birds
Throughout the migration routes of birds around the world, we will find that most of the migration routes of birds have many similarities. For example, some areas on the ground are places where many birds will pass, and some areas are places where many birds will avoid. According to the basic law that most bird migration, which breeds in a certain area, overwinters in a certain area, people have summed up some routes that most birds pass through, which are called "passages" in bird migration.
The research on the historical data of bird migration in Europe, Asia and Africa shows that there are five "passages" in bird migration in these three continents. There are some overlapping and overlapping phenomena among these five "channels". In fact, each "passage" contains many migration routes of different species or different families and groups of the same species that are roughly parallel or staggered and complicated. China is a part of East Siberia-Tibet/Ganges and Heilongjiang-China. Part of western China is part of the Siberian/Kazakh-Pakistani/Indian Corridor.
(b) Direction of bird migration (navigation)
Migratory birds migrate along specific routes year after year, and return to breeding and wintering sites accurately every year, which shows that they have accurate navigation and positioning functions. The navigation mechanism of birds has always been a research topic of great concern, but so far there is still no perfect explanation of bird migration mechanism in theory.
Birds can find their way from thousands of miles away, which has always been one of the mysteries of magical nature. What do they rely on to decide their own course? Polaris? The sun? The moon? Wind? Climate? Or geomagnetism? Where does their sense of direction come from? This has always been a mystery in nature. Scientists have observed through environmental records, radar, flight tracking and remote sensing that birds often rely mainly on vision to determine their flight direction through the positions of the sun, moon and stars in the sky. In addition, topography, rivers, thunderstorms, magnetic fields, polarized light, ultraviolet rays, etc. Are the basis for birds to fly thousands of miles without getting lost. Recent studies also show that there are nerve cells in the cortex of bird beak that can distinguish magnetic fields, and nerve cells called pineal gland play an important role just like vertebrates' sensory organs for light. Many electrophysiological experiments on mammals and homing pigeons show that some pineal cells can respond to small changes in magnetic field strength.
According to the observation and experimental results, people can divide the bird orientation mechanism into two categories: visual orientation and non-visual orientation.
1, visual direction (visual direction)
(1) solar direction
(2) Stellar direction
(3) Landmark positioning
2. Non-visual orientation.
(1) geomagnetic direction
(2) auditory orientation.
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.
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.
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.
Migration has brought many benefits to birds, mainly in the following aspects: (1) Birds always live in the most suitable climate and have rich and diverse 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.
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.
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.
Second, the origin of bird migration
At present, there are three different views on the origin of bird migration: ① Birds originated in the south. As the continental plate drifted from south to north, many birds were taken to the north, so they tried to return to their hometown in the south, forming 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.
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, mainly as follows:
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.
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.
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. Birds that are known to be able to locate themselves by using stars include diphtheria finches.
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.