Reasons for the extinction of fear birds

People are quite familiar with and concerned about the extinction of dinosaurs. Another equally extinct animal, also associated with the word "giant", looks strange. This animal is called "fear of birds". The fear bird is a wingless bird that lived in New Zealand a long time ago. In the past, people always thought that the extinction of the largest bird known to mankind was the result of indiscriminate killing, but scientists found that the responsibility for the extinction of this bird was not entirely on human beings.

The story of fear of birds usually unfolds like a legend. A long time ago, this big bird like an ostrich lived happily in a land with white clouds. Maori people call this land "Otiloa", which is now New Zealand. About 700 years ago, an influential day came, and the first humans came there. They are Polynesians. It is said that they came from Hawaii by canoe and found a wingless bird on New Zealand Island, which is easy to kill and can provide them with nutritious food. This kind of bird is a fear bird. Adult moas are 3.5 meters tall and weigh 250 kilograms. Meat is delicious. Within six centuries, the Maori killed all these unfortunate feathered behemoths. Just like the dodo, the fear of birds has since become a symbol of human greed, or in modern terms, a prominent example of unsustainable development. But is this really the case? Scientists have raised great doubts about this statement through molecular testing, that is, should Maori be so deeply blamed for this disastrous consequence?

Why did the number of fear birds drop so much before the arrival of mankind? Gimel put forward several novel theories, one of which is that the number of fear birds has decreased due to volcanic eruption. He believes that climate change is not the reason for the decline in the number of fear birds because there is no convincing evidence for this view. Volcanoes often erupt around lake taupo, the center of New Zealand's North Island, destroying the local fear bird living area again and again.

In addition, before the arrival of humans, the fear of birds had natural enemies, such as a giant eagle in New Zealand. In fact, before humans arrived in New Zealand, the number of fear birds began to drop sharply. Even before humans threw the first spear, the fear of birds was a local vulnerable group and was very vulnerable to external attacks. There are 10 species of fear birds, and the biggest one is fear birds. A team of biologists led by Neil Gimel, a biologist at the University of Canterbury in New Zealand, extracted DNA from the largest preserved dinosaur skeleton, and then obtained the DNA sequence through a computer model based on mutation. As a result of population mixing, mutations occur in each generation. By examining these tiny genetic changes, scientists can turn back the molecular clock to see how a species evolved, and they can also infer the number of this population: the larger the number, the more extensive the genetic changes!

After carefully studying the data of birds' fear, Gimel's research team deduced the number of such birds, which they called "low to alert level". 1000 years ago, millions of dinosaurs lived in New Zealand. The researchers said that with the addition of nine other species of fear birds, about 3 million to 1 0.20 million fear birds lived on the islands in northern and southern New Zealand from10,000 to 6,000 years ago. When humans first arrived there around 1280, the number of fear birds was less than 159000. By the beginning of the18th century, there were about 60,000 more. However, there is a more convincing explanation that the sharp decline in the number of fear birds is caused by the spread of diseases, such as bird flu, salmonella or tuberculosis, which are brought there by migratory birds from Australia and other places. Of course, if humans don't reach that place, the number of moyamoya can rebound. Because the arrival of human beings destroyed their living environment and killed moyamoya, their number was further reduced.

Gimel's research results were published in academic journals published by the British Academy of Sciences. According to the research report, the reasons for the extinction of the fear bird are very complicated and have been buried with the passage of time. The article said: "If our new estimate of the number of fear birds is correct, then we need to reconsider the factors that affected the number of fear birds before the arrival of humans. Maybe we can better understand and solve the problem of modern environmental protection by summing up the lessons of the past. "

Although the upper limbs of moa have degenerated like ostriches, its body is big and its lower limbs are short, so its running ability is far less than that of ostriches. The biggest difference between a moa and an ostrich is that its neck is covered with feathers, while an ostrich's neck is bare and longer than a moa's neck. It has three toes, and an ostrich has two toes.

/kloc-in the middle of the 0/8th century, European immigrants came to the island, which brought bad luck to the moa. I'm afraid poultry meat is a delicacy for European immigrants. Because it is huge, it is difficult to hide. Europeans can easily catch them and often kill more than a dozen at a time. Fear of poultry meat has become an important source of meat for these European immigrants. At the same time, due to the arrival of European immigrants and the increasing number of local aborigines, a large-scale burning and reclamation began, and the habitat of the fear bird was completely destroyed, and the fear bird was starved to death in large numbers because it lost its foothold. At the same time, for fear that birds would destroy crops, they killed a large number of fear birds to protect crops. In addition, domestic dogs and mice that came to the island with Europeans have also become natural enemies of moa. They also give a fatal blow to the fear birds.

By the end of 18, the number of scary birds was very small, and it became more and more difficult for people to catch scary birds, and 1800 was the last year when people could catch scary birds. For the disappearance of bird fear, human beings are undoubtedly the culprit. But I'm afraid it's unfair to put all this account on the head. The reasons for the rapid disappearance of the fear birds are more complicated.

Scientists' simulation experiments on the dynamic changes of the number of fear birds show that the mortality rate of adult fear birds was high at that time, while the birth rate was very low. The high mortality rate may be related to the natural enemy (human being is the protagonist) killing this unsuspecting animal at will. Natural disasters (such as volcanic eruptions) are also one of the reasons.

As for the low birth rate, it can be explained that the reproduction rate of giant animals is very low, but correspondingly, their life span is very long (mice, insects and other small animals have high reproduction rates, but they are short-lived ghosts). On an island with limited area and food, there is no restriction of natural enemies, and the high reproduction rate is very unfavorable to the survival of this huge animal, the fear bird. There must be a mechanism in the genes of the fear birds to limit the "population expansion", otherwise they will destroy themselves because of excessive reproduction and eating up the edible plants on the island. It is said that the fear bird only lays one egg at a time.

However, if there were no foreign invasion in those years, the low reproduction rate of the fear birds would not constitute an extinction crisis. Scientists say that archaeological records show that humans hunted the New Zealand moa, which may be the reason behind the extinction of the New Zealand moa.

Before the arrival of human beings in 1300, there were nine flightless bird-fearing species in New Zealand. Within a century, all nine species disappeared. MortenAllentoft of the University of Copenhagen and his colleagues studied the DNA of 28 1 fossils of four species of fear birds. They found that the genetic diversity of moa remained unchanged for 3000 years before extinction, which was a sign of population stability. "We can only attribute the disappearance of our fear of birds to human beings." Allen tofte said.

Allen tofte's findings contradict the earlier research results of Neil Gimel of Moguel Otago University. In 2004, Gomel studied the mitochondrial DNA of dinosaur fossils and found that the dinosaur population in New Zealand was about 3 million to12 million from 4000 BC to AD 1000. Another independent study shows that when humans first arrived in New Zealand 300 years later, there were only 159000 species of fear birds, so Gomel speculated that there must be other reasons leading to a sharp decline in the number of fear birds before humans hunted them.

However, these estimates are not reliable because DNA is not the best record of species size. Allen tofte said that DNA can only show the changing trend of species number. This latest study "seems to be devoted to studying the possible reasons for the sharp decline of the species of fear birds", said RossMacPhee of the Mammalian Museum of the National Museum of History in new york, USA, who was not involved in the study.

In addition, it is not easy to separate human impacts on animal species from other impacts, such as climate change. When humans arrived in America and Australia, mammoths and other large animals became extinct, which made people doubt the causal relationship between them. A study found that the mammoths in the Arctic disappeared after the vegetation changes caused by climate change, rather than being over-hunted by human beings.