There is a hapless gray goose that is accidentally trapped in a fishing net and cannot fly. A little boy rushed to break the rope that was wrapped around it. As soon as the net was disconnected, it hurriedly spread its wings and flew high into the air, chasing its companions. Next, the flock of gray geese tirelessly flapped their wings and began the migration journey of nine deaths.....
This clip from "Migrating Birds" has touched countless audiences. It has to be said that bird migration is one of the most attractive natural phenomena on earth.
Every year, tens of billions of birds migrate back and forth between breeding grounds and wintering grounds thousands of kilometers apart, performing a miracle of life.
However, we humans know very little about why they migrate. Many people simply think that they migrated south to keep out the cold. But in fact, this view has long been outdated.
With the deepening of research, we will find that the migration of birds is full of endless mysteries, subverting human cognition again and again. And before exploring the causes, let's start with a peculiar bird to dispel misconceptions.
The Flat-billed Puffin (Ancient Murrelet) has long been regarded as the "four unlikes" of the bird family. It has a sparrow-like bill, a penguin-like body, flippers like a duck, and chicks with feathers the same color as a chick. What is most different from other birds is that its legs are born on the tail, and when it stands upright, it walks like a faltering old man.
However, they seem clumsy and fly about 8,000 kilometers a year, spanning the entire North Pacific Ocean and traveling to and from the United States and Asia. For example, they will breed in western Canada and then fly thousands of miles to the oceans of China, Japan and South Korea to spend the winter. It is also the only bird known to straddle the North Pacific.
Flat-billed puffin (Ancient murrelet)
At first, people thought that migration was a big trick for them to avoid winter. However, the latest research finds that this is not the case. The places they travel to and from also have similar temperate climates at the same time. Theoretically, if they stay in their breeding grounds in winter, the environment there will allow them to survive.
So why do they migrate so far? Scientists are puzzled by this and still can't find the answer. However, this example clearly overturns our inherent belief that birds do not migrate because of cold climates. After all, in the late winter of the waxing moon, there is no shortage of birds around us, such as sparrows.
Funny GIF: Sparrow with an arm
We know from a young age that migration refers to the large-scale directional movement of wild animals due to changes in time, and the "migration" of aquatic animals is also known as "migration". But no group of species has been as intriguing as the migration of birds. But not all birds have migratory behavior.
According to the characteristics of bird migration activities, we can divide birds into two categories: resident birds and migratory birds. As the name suggests, a resident bird is one that stays in the same place all year round and does not migrate.
For example, the less flight ability of the chicken-shaped birds. Most resident birds live in warmer climates, but there are also resident birds in alpine regions, such as snow chickens living in the Himalayas and emperor penguins in Antarctica.
Hidden snow chicken
Migratory birds, on the other hand, are birds with certain migratory behaviors. It is mainly subdivided into winter migratory birds, summer migratory birds and so on. Winter migratory birds refer to birds that come to a certain place in autumn and winter to overwinter and leave in spring, such as wild geese, swans, wild ducks, etc.;
Summer migratory birds are birds that come to a certain place in spring and summer and leave in autumn. During this period, they often undertake the important task of breeding, so they are also called breeding birds, such as cuckoos, orioles and so on.
Interestingly, the distinction between migratory and resident birds is not absolute. The same bird species may exhibit different residency types in different areas or even in the same area. For example, the original red-crowned cranes bred in Hokkaido, Japan, are migratory birds, but over time some red-crowned cranes have given up the instinct to migrate and become local resident birds;
Another example is the black capuchin of the passeriformes, which are resident birds in Hainan Island, Yunnan and other places in southern China, and migratory birds in the Yangtze River Basin and North China. So, what exactly determines the migration of birds? Why are some birds, which were migratory birds last year, but have become resident birds that stay in the north for the winter this year?
Some scientists have speculated that the migratory habits of birds date back to the Ice Age in 10,000 BC. When the snow and ice season in the Northern Hemisphere arrives, some birds are forced to leave their homelands to find places to feed. When the cold wave recedes, they fly back from elsewhere.
But when the cold wave hit the next year, the birds that did not migrate last year were induced by their peers to join the migration team. Year after year, the migratory procession gradually expanded, and finally formed the annual migration of migratory birds.
That is to say, the periodic erosion and retreat of glaciers cause birds to form a genetic instinct of migratory organisms that are corresponding to the regular round-trip, so they form habits from generation to generation.
An endless Antarctic ice sheet
However, this theory has certain flaws, it does not explain why some birds do not migrate, and the ice age accounts for only 1% of the bird's survival history. For such a short period of time, the heritability of birds may be limited.
Another major view is the "energy consumption theory", and some scientists believe that migratory birds migrate because of their own "energy consumption". This is because the migration process requires a lot of energy.
For example, in the process of birds migrating from the north to the south, the energy consumed by day and night is 6 times more than under the conditions of settlement at 30 °C. Therefore, in the winter season, "migration" consumes much more energy than "settlement".
In recent years, the University of Arizona in the United States, W. Two scientists, Alice Boyle and Courtney Conway, have come up with new ideas for studying bird migration. They believe that the reason is not as mysterious as humans think, and that they probably migrate purely because they are hungry.
This new hypothesis was obtained by studying the habits of 379 species of bullies living in the New World. Bulbophylls are short for birds of the family Tyrannosaurus, which are mainly distributed in tropical South America, with a small number of distributions from Central America to North America.
As the largest family of birds, this family contains both resident and migratory birds, and the two sometimes switch to each other. Migration occurs because food shortages occur in some areas during the cold, forcing them to leave their homes and migrate to areas with high temperatures and abundant food.
Red is the distribution of the Bullhead
Researchers believe that this new hypothesis can also be popularized to the vast majority of birds. In the case of the northern hemisphere, the north is suitable for bird breeding in summer, while the temperature in the south is too high and the impact of human activity is too large to be suitable for most birds to hatch as young birds.
The north is sparsely populated and safer for birds. In winter, however, birds face the survival problem of being covered in snow and ice in the north and unable to find food, so they choose to move south. This hypothesis also explains why the same bird can transition between resident and migratory birds.
If the food in the north is continuous throughout the year, even if the temperature is low, they do not mind staying for the winter, and the migratory birds become resident birds. But if there is no food in the winter in the north, they will also choose to move south in order to survive, and the resident birds will become migratory birds.
The aforementioned red-crowned crane changed from a migratory bird to a resident bird because the locals continue to feed them regularly during the winter to give them a stable food source. The same phenomenon occurs in the common mallard duck. The mallard is a migratory bird in most of its range. But because there is an unfrozen water surface in Beijing's city parks, there are tourists feeding. Today, a large number of mallard ducks can also be seen there, some of which are individuals breeding and residing in Beijing.
Rise and fall of the water bird mallard
The other two common birds in eastern China, the blackbird and the white-headed grebe, were still considered resident birds until the early 2000s. But in the past decade or so, they have appeared in more and more northern cities, even including Liaoning and Jilin in northeast China, and there has been a phenomenon of migration.
So why don't birds stay in warm areas with plenty of food all year round? Because food is not the only factor that affects survival. Although the equatorial region is warm all year round and there is no shortage of food, there are many natural enemies and the pressure of competition is also great. When the north warms up, there is more food in the north, and there are fewer predators and competitors, so the birds will fly back again.
Again, some non-migratory birds such as sparrows, crows, etc. do not have food shortages? Some researchers believe that this may be related to the different wintering and breeding environments required by different birds. For small forest birds that do not migrate, they can be fed in the winter by looking for grass seeds, berries, etc. on the ice and snow.
From this point of view, new topics are constantly emerging in the study of bird migration for us to explore. Nowadays, under the intervention of climate change, human influences and other factors, the distribution range of some birds has undergone global changes, and new migration and proliferation behaviors have been formed accordingly.
Perhaps in order to survive, they will not only be able to migrate tirelessly, but also change their habits for thousands of years.
Ancient murrelet . Wikipedia.on 16 November 2019, at 03:18 (UTC).
Bird flies 16,000-kilometre Pacific circuit for no clear reason7 August 2015 By Rachel David.newscientist.com
Boyle W A, Conway C J. Why migrate? A test of the evolutionary precursor hypothesis[J]. American Naturalist, 2007, 169(3):344-359.
Boyle W A, Conway C J, Bronstein J L. Why do some, but not all, tropical birds migrate? A comparative study of diet breadth and fruit preference[J]. Evolutionary Ecology, 2011, 25(1):219-236.
Wen Cheng,Xu Yongchun. Bird migration The miracle of life in China[J].Forest and Human beings, 2019(05):8-27.
YAO Yi, XIAO Hui-yue.April 1-7, 2019 Bird Love Week, Maintaining a Community of Life, Focusing on Migratory Bird Migration[J].Forestry and Ecology, 2019(04):2+49-50.
Documentary: Migrating Birds
Mr. Sea World, 2016(11):6-7.