It's an X-ray image of a bird that holds a huge bird egg inside its body, and its mass is about a third of that of the bird that carries it. If humans also have this ratio when pregnant, then it is equivalent to carrying a baby of nearly 30 pounds in the belly, the strange bird in the picture is called Kiwi bird, which is a unique species in New Zealand, the Kiwi bird is loved by New Zealanders because of its unique appearance and cuteness, it is their spiritual symbol, New Zealanders even call themselves kiwi directly, and even worship the kiwi as the national bird.
<h1 class = "pgc-h-arrow-right" > cute Kiwi bird</h1>
Although the kiwi is a bird, but the wings have been completely degraded, their feathers are as thin as thin and fluffy hair, so they can not fly, and the adult kiwi weighs about 2 kg. Since the chick-wicked bird is called "keee-weee", it is also known as the Kiwi bird. Kiwi are timid by nature, easily frightened, and spend most of their time at night to escape attacks from beasts of prey. Unable to fly, their skeletons do not have hollow structures like other birds, but have bone marrow like mammals, and their bones are strong enough to support larger weights and have a strong running ability.
A kiwi bird that runs at night
Kiwi birds have poor vision, and scientists have found that about a third of kiwi birds have eye damage. Kiwi birds have a long pointed beak, and the nostrils are located at the end of the long beak, and because the eyesight is getting lower and lower, their noses are very sensitive and have a strong sense of smell, so that they can accurately smell food during the probing process with the pointed beak, so as to prey. Their main diet include earthworms in the dirt, insects, spiders and other invertebrates. The Kiwi bird can live up to thirty years and is endemic to New Zealand and is the national bird and symbol of New Zealand.
An obese kiwi bird
<h1 class= "pgc-h-arrow-right" >Why are kiwi eggs so large? </h1>
Although the size of mature kiwi birds is a little smaller than that of domestic chickens, they can produce eggs that can reach more than one-third of the female bird's body weight, only a little smaller than ostrich eggs, in addition to the unique size of the eggs, the proportion of egg yolks in the kiwi eggs is also relatively high, reaching 60% of the entire egg, much higher than the usual birds 30% to 40%.
When you see the kiwi birds in the picture above, do you think that their size is round and rolling, in fact, these are female kiwi birds with oversized eggs. A pregnant female kiwi must consume three times more calories than usual to feed the developing eggs in its body. Its furry belly will eventually drag to the ground and become so large that it must not be eaten in the last days of pregnancy, because there is almost no room in the stomach to hold food.
The skeleton structure of a kiwi bird
Scientists used to think that these huge eggs were the result of a strange evolutionary catastrophe. Perhaps the ancient kiwi was larger, and as they shrank in size, they were unable to evolve smaller eggs. Since the female can still survive in this case, there is no need to remove the huge egg.
But scientists have taken a different view, and in a 2013 paper in the journal Science, they analyzed the fossil remains of the direct ancestors of modern kiwi birds and found that they corresponded to a much smaller bird whose ancestors were only a quarter the size of the smallest surviving kiwi species. So there is a good chance that it evolved from a small bird to its size today. So if that's the case, what good can a kiwi bird do by producing an egg of this size?
Scientists believe that this evolution of the kiwi is not accidental, but to allow the small kiwi to mature faster. After they come out of their shells, their stomachs also contain some undifferentiated egg yolks and other nutrients, and for the first two and a half weeks of life, they can live on these yolks. In other words, you could even imagine that kiwi birds are more mammalian than mammals, evolving a mechanism similar to that of laying eggs alive, with a lot of excess yolks replacing breast milk. So this way they reproduce is more like mammals than birds. The huge eggs allow them to develop fully by the time they emerge from their shells, so they have the ability to run alone and avoid predators at birth, and their parents leave these young birds almost immediately after hatching.
<h1 class= "pgc-h-arrow-right" > the fate of kiwi populations</h1>
Originally, there were almost no native mammals in New Zealand except for bats, and now some other predatory mammals such as stoats and weasels are brought by sailors when they entered New Zealand. It is because of these artificially invasive species that the kiwi was once threatened with extinction. Since the pregnant kiwi has almost lost its mobility, in the eyes of some carnivorous mammals, it is a lying lunch.
A century ago, New Zealand's kiwi number was in the millions, but today, the kiwi population is estimated to be only about 35,000.
However, New Zealand's protection measures for kiwi birds are becoming more and more perfect, and kiwi birds have also become New Zealand's national bird, and it is believed that the number of kiwi birds will gradually recover in the future.
Resources
[1] Blind free-living kiwi offer a unique window into the ecology and evolution of vertebrate vision[J]. BMC BIOL, 2017.