Su Dongpo, a famous writer in the Northern Song Dynasty, wrote a famous poem in "Yu Qian Monk Lujunxuan", which is called "It is better to eat without meat than live without bamboo." But for the giant panda, it doesn't matter if it lives without bamboo, but it doesn't matter if it doesn't have bamboo to eat. It became a "bamboo hermit" not because it liked the elegance of the bamboo forest, but because it was easier to eat bamboo...

In the eyes of the general public, giant pandas eat bamboo, just like Buddhist disciples who are vegetarians It is their duty, just like horses, oxen, sheep and donkeys. In fact, this is not the case. In terms of biological classification, giant pandas are a member of the order Carnivora after all. Not to mention that its ancient ancestors were veritable carnivores, even the current body structure of the giant panda still retains some characteristics of its ancestors during its evolution. For example, giant pandas have sharp canines and split teeth. The canines are especially thick and long, with tapered crowns. These are necessary teeth for tearing animal flesh. They are similar to the teeth of lions, but are obviously different from the teeth of herbivores, cattle and sheep. Moreover, giant pandas have strong horny claws at the ends of their fingers and toes, similar to black bears.

Growing such "fangs" and "claws" is naturally used for hunting. G. Cuvier (1769-1832), the famous naturalist in the early 19th century and known as the "dictator of biology", once pointed out that all the organs of any organic individual form a complete system, and its various parts mutually consistent and interactive. In this way, the appearance of the entire animal body can be reasonably judged and inferred from one bone or one organ. Of course, he once "overturned" when identifying the clawed animal (an extinct odd-dactyl animal with a very special shape). In his opinion, ungulates that eat plants would not have claws (because they would not use them), so he identified their feet as carnivorous. In fact, clawed beasts love to eat leaves. They often grab tree trunks with their front feet (claws formed by specialized hooves) and stretch their heads to eat leaves on the trees. But this is only a small probability event after all. If Cuvier was asked to identify the attributes of giant pandas through bones, I am afraid that he would still classify them as carnivores based on their fangs and claws without hesitation.

In early 1984, staff at the Giant Panda Field Observation Station in Wolong Nature Reserve, Sichuan, were at altitude. On the 2,700-meter hillside, pig bones are roasted on a bonfire until they are delicious, and a trap is set up. If a giant panda is found to be old, weak, sick, or disabled, it will be immediately carried down the mountain and sent to a breeding ground. artificially reared. Sure enough, on January 3, the scent of pig bones attracted a giant panda. After inspection, scientific workers found that this was a female adult panda with a strong body, good development, and was not old, weak, sick, or disabled. among them. After it had eaten its fill of pig bones, the staff let it go. Unexpectedly, the next day, the giant panda came again and ate with gusto. As a result, it came back on the third day, and the helpless staff had to remove the trap. Unexpectedly, it was this giant panda that actually followed them and walked into the "Wuyiteng" in a big way. Out of respect for the "distinguished guest", everyone cooked a basin of sugar corn porridge for him (people named him "Beibei"). "Beibei" was not polite at all. He swept them away and walked away. Unexpectedly, it became addicted to eating it. It "visited" the observation station regularly at 5 o'clock in the afternoon every day, and had a full meal of "delicious food" such as sugar corn porridge or sugar cane every day. When scientific workers gave "Beibei" mutton to eat, it seemed the happiest and ate several kilograms of mutton at a time! Experts were worried that it would become dependent and transform from a wild giant panda into a captive giant panda, so they captured it and carried it to a mountain more than 50 kilometers away from "Wuyipeng". Unexpectedly, dozens of days later, "Beibei" came back again. As soon as this rude guy got into the "May 1st shed", he rummaged through the boxes and made a mess like a house ransacked. People stayed away, and "Beibei" became more and more proud. She actually took a piece of more than ten kilograms of mutton and disappeared into the bamboo forest! This is really irritating and funny, and the giant panda’s love of eating meat can be said to be fully reflected in Beibei.

Since the giant panda is an authentic carnivore from the perspective of digestive tract anatomy, physiological characteristics and species evolution, why did this "flower monk" become a staple food of bamboo? Similar to Lin Chong in the novel "Water Margin", giant pandas in reality were probably forced to climb mountains. There is no other reason than fierce biological competition. Today's giant pandas are distributed in the Hengduan Mountains on the eastern edge of the Himalayas, where rare wild animals and plants are abundant. Take the Minshan Mountain System as an example. The vertical spectrum of mountain climate here is extremely obvious, and it is known as "a mountain has four seasons." Below an altitude of 1,700 meters, except for a few nature reserves, such as Tangjiahe Nature Reserve, most have been cultivated into farmland, and what remains or is naturally regenerated is zonal evergreen broad-leaved forest. Giant pandas will occasionally visit this area in winter. Remote place. This is also the distribution area of ​​muntjac, tufted deer, goral, yellow-throated marten, big civet, small civet, takin, black bear, weasel, red fox, pig badger, ocelot, civet, wild boar, golden pheasant, giant salamander and other animals. .

At an altitude of 1700-2300 meters, there is a mixed evergreen and deciduous broad-leaved forest. The zonal vegetation of evergreen broad-leaved forests has been destroyed, and the river valleys are mostly farmland. The arrow bamboo here is the staple food of giant pandas. Sympatric animals include golden monkeys, takin, macaques, Tibetan emirates, black bears, yellow-throated martens, big civets, small civets, jackals, pig badgers, red foxes, weasels, gorals, tufted deer, serows, and wild boars. , civet, ocelot, golden pheasant, etc.

The mountainous dark coniferous forest belt is located at an altitude of 2100-3400 meters, and the alpine canyon area at an altitude of 3000-3900 meters (or 4000 meters) is the subalpine dark coniferous forest zone. Bamboo, the staple food of giant pandas, is mainly distributed in the above two areas. There are also many animals that are sympatric with giant pandas, including golden monkeys, takin, leopards, clouded leopards, white-lipped deer, sika deer, red pandas, black bears, blue sheep, gorals, serows, forest musk deer, jackals, macaques, Tibetan Emirates, otters, tufted deer, red-bellied pheasant, blood pheasant, blue-eared pheasant, etc.

It is easy to find that there are many kinds of carnivores distributed in Minshan Mountain. If giant pandas also eat meat as their main food, then this place is far from being a "paradise" for them. Giant pandas will encounter different competitors in various climate zones: black bears, yellow-throated martens, giant civets, small civets, jackals, red foxes, and leopard cats in evergreen broad-leaved forests and mixed evergreen and deciduous broad-leaved forests; dark mountain areas The coniferous forest belt and the subalpine dark coniferous forest contain leopards, clouded leopards, jackals, and historically there may have been South China tigers; further up, the snow leopard is the absolute king of the alpine shrub meadow belt. Giant pandas have no advantage over these carnivorous competitors. For example, in 2014, a 3-year-old giant panda in Tangjiahe National Nature Reserve in Sichuan was suspected of being attacked by a yellow-throated marten, causing its intestines to be exposed. As it evolves to this day, the giant panda's limbs are short and thick, and its chubby body can no longer hunt dexterously and at high speeds. Its eyesight has also gradually weakened, making it difficult to see potential prey as early as possible... People have recorded wild giant pandas eating meat Most of them are rotten corpses, which is enough to prove that its active hunting ability has been completely lost. As for "little snacks" like bamboo rats, they cannot feed the huge giant pandas anyway.

To survive, giant pandas have evolved unique living habits. It took off its carnivore "gown" and burrowed into the lush bamboo forest. This may be a tenacious adaptation, or it may be a helpless choice. But in any case, the competitive pressure between giant pandas and other animals has suddenly reduced - in the giant panda's living area, there are far fewer species of bamboo-eating animals than carnivores.

Giant panda "Tian Tian" in Washington National Park in the United States eats fruit ice. In addition to mainly eating bamboo, captive giant pandas can also get a small amount of concentrated feed, fruits, and vitamins and trace element additives

Judging from the tooth structure, the first molar of the giant panda's upper jaw is square, and the first molar of the lower jaw is square. The molars are rectangular in shape, with multiple cusps and tooth folds, and the tooth crown is multi-nodular; the maxillary second molar is wide in front and narrow in the back, and the mandibular second molar is square, with multiple tooth cusps and tooth folds on the crown. It is multi-nodular in shape; the third lower molar is round with multiple tooth folds. These molars have wide crowns and long roots. The outer layer is enamel, also called enamel; the inner layer is chalk, also called dentin. The enamel layer is composed of several glaze pillars. It is hard and wear-resistant and has adapted to eating bamboo. In addition to teeth, giant pandas also have very developed chewing muscles hanging on both sides of their cheeks, which naturally come in handy for chewing rough bamboo.

Giant Panda Skull

At the same time, the wrists of the giant panda’s forelimbs have also undergone extremely obvious specialization. Its forefoot bones are composed of carpal bones, metacarpal bones and phalanges. On the inside of the carpus, there is an extremely developed sesamoid bone, which is a characteristic of the giant panda, that is, the radial sesamoid bone (radial carpal bone). It is attached to the muscles of other animals that are born in the thumb, making the radial carpal bone very flexible and becoming a kind of "False thumb", while the original thumb becomes parallel to the other four fingers. From a functional point of view, the giant panda's front paw has six fingers, which is entirely for the convenience of eating bamboo. The "pseudo thumb" plays a role in assisting in holding objects. It is very flexible and convenient to grasp bamboo. This makes it more convenient for giant pandas to eat bamboo and obtain greater net energy gains.

Relying on specialized teeth and "pseudo-thumbs", giant pandas are able to feed on bamboo. It eats bamboo not by cutting it, but by biting it. The way it eats bamboo is very interesting. The giant panda came to a bamboo forest, sat down, bit off the bamboo, took one with his left forelimb, and stuffed it horizontally into his mouth. "Click" and bite off a section, about 20-30 centimeters, which is exactly the lateral distance of its teeth. Then, throw it away. He took one with his right forelimb, stuffed it horizontally into his mouth, and bit it off with a "click". Alternate left and right in this way until all the surrounding bamboo is eaten. The giant panda will stand up again, take a few steps forward, sit down again, and eat bamboo "from both sides" again...

Giant panda "Bing Xing" eats bamboo at the Madrid Zoo in Spain< /p>

Of course this only solves the problem of eating bamboo into its mouth. To really rely on bamboo for survival, giant pandas also need to have the ability to digest bamboo. Its intestines and stomach still retain the color of a carnivore. The stomach is a single-chamber glandular stomach with many glands distributed in the gastric mucosa, such as cardia glands, fundic glands, corpus glands and pyloric glands. Fundic glands are composed of extremely rich chief cells and parietal cells. Such rich glands, similar to meat-eating animals, can secrete sufficient digestive enzymes and gastric acid. Their intestines are short and simple in structure, only 4.5 times their body length, and they have no cecum. These structures are similar to those of general carnivores.

In order to digest bamboo instead of meat, the giant panda's digestive system has evolved to develop more abundant single-cell and multi-cell mucus glands. There are many mucus glands in the oral mucosa and lamina propria of the tongue. There are submucosal glands that mainly secrete mucus throughout the esophagus, including a well-developed pyloric gland area, mucinous duodenal glands, and the mucosal epithelium of the entire intestine from the duodenum to the rectum. The secretions of these mucus glands can, on the one hand, protect the mucosal surface of the digestive tract from damage, and on the other hand, facilitate the passage of relatively rough bamboo stems, leaves, bamboo shoots and other foods, acting like a "lubricant"; At the same time, it also allows loose bamboo residues to stick together into a ball and wrap a layer of mucus to facilitate defecation. Captive giant pandas tend to secrete excess mucus due to their fine feed, which often accumulates into clumps within a certain period of time and is excreted from the body through excretion.

As the only large animal in the order of Carnivora that feeds mainly on bamboo, the diet of the giant panda varies with the mountain range and the season. In spring and autumn, they love to eat bamboo shoots (spring bamboo shoots and autumn bamboo shoots). Tender and juicy bamboo shoots are rich in protein and are a rare delicacy for them. However, bamboo shoots grow very quickly and can reach the height of a mature bamboo within a few days. At the same time, the nutrition and taste will rapidly deteriorate as the internal fiber content increases. Therefore, every spring, wild giant pandas "get up early and stay late" during this period, just to grab time and eat the annual delicacies before the bamboo shoots grow taller. In autumn, the protein content of bamboo leaves is the highest in the year, often reaching 17.5%, and bamboo leaves are also the part with the highest nutritional value among the various organs and tissues of the bamboo plant. Therefore, the giant pandas at this time, regardless of gender and age, feed on the new branches and leaves that have grown that year. After autumn, frost and snow fall, and the bamboo leaves gradually wither. The remaining old leaves that wither on the mountains not only have poor nutritional value, but also have poor palatability. Generally, giant pandas eat less or refuse to eat. However, some elderly individuals, whose teeth have been worn down due to the destruction of bamboo forests on hillsides and valleys, are unable to bite off bamboo stalks, so they have no choice but to "make up for it" in the harsh winter by eating withered leaves to satisfy their hunger. In contrast, bamboo stalks are a common part of giant pandas' food throughout the year, especially in winter. Even when bamboo shoots are available in spring and summer, giant pandas will also eat a small amount of bamboo stalks.

In addition, with the collection of studies in different regions, it was discovered that giant pandas eat more than one kind of bamboo, and not all bamboos are eaten. my country is one of the areas with the richest bamboo distribution, with about 40 genera and 400 species. As of 2022, professionals have determined that bamboo, the staple food of giant pandas, has 107 species and 1 variant in 16 genera! Among them, cold arrow bamboo, lack-bract arrow bamboo, Qingchuan arrow bamboo, Bashan wood bamboo, and Ere bamboo are all bamboo species that giant pandas like to eat. For example, the giant pandas in Wolong Nature Reserve feed on the young bamboo stalks of the bamboo in winter, and also eat the remaining leaves; in spring and summer, they like to eat the bamboo shoots of the cane bamboo, as well as the bamboo stalks; in the autumn, they all feed on the branches and leaves of the bamboo. Giant pandas in the Qinling Mountains eat bamboo leaves of Bashan wood bamboo as their staple food in the lower mountains from October to May of the following year, as well as bamboo stalks and bamboo shoots; from June to September, they move up to the Qinling Arrow Bamboo Forest to feed on bamboo shoots and bamboo stalks. . Although the protein content of bamboo stalks of Qinling arrow bamboo is not as good as that of bamboo leaves, the bamboo leaves are sparse, so they would rather eat bamboo stalks than bamboo leaves.

Giant panda "Fu Bao" is eating bamboo leaves given by the breeder at Everland, South Korea

Although there are many kinds of bamboo, and it seems that giant pandas have a rich dining table, in fact, from an energy perspective, bamboo is an extremely inefficient food. Bamboos belong to the family Gramineae, but unlike grasses, they have woody stems and are a type of shrub plant with high fiber content. Plant tissue is mainly composed of two parts: one is the cell content composed of soluble nutrients; the other is the cell wall composed of tough and fibrous cellulose, hemicellulose and lignin. For bamboo, its main components are cellulose and lignin, which account for about 95% of the bamboo material, which cannot be digested by giant pandas. Among different parts of the bamboo plant, bamboo leaves have the highest protein content and the lowest cellulose and lignin content. If the ratio of protein to cellulose and lignin is used as the nutritional quality ratio, the nutritional level of each part of the bamboo plant is ranked as leaves > young shoots > old shoots > branches > culms.

The nutritional value of bamboo plants is inherently low, and the digestive system of giant pandas is not yet capable of making full use of it. Typical herbivores such as deer and sheep have very long intestines (the intestine of deer is 15 times the body length and that of sheep is 25 times). The forage they eat often stays in the digestive tract for more than 24 hours, which is conducive to full digestion. However, the intestinal tract of a giant panda is only 4-5 times its body length, and food only remains in the digestive tract of the giant panda for less than half a day. As a result, after the bamboo stalks ingested by the giant panda pass through the intestines after being chewed, the slices of the bamboo stalks remain intact. The original parts of various tissues (although they have been deformed to varying degrees). The "cortical cells" in the outer tissue are not completely separated, only the inner parenchyma cells are digested, leaving gaps in the tissue. After the bamboo shoots are eaten by giant pandas, the parenchyma tissue in the bamboo shoots is almost completely digested. However, because they chew the bamboo shoots very roughly and pass through the digestive tract quickly, the vascular bundles in the bamboo shoots are separated but still intact when viewed in slices. After digestion, the bamboo leaves basically maintain the original bamboo leaf structure from the section. Only some alveolar cells and some mesophyll cells are digested, especially the mesophyll cells near the lower epidermis are digested more, while the mesophyll cells in the bamboo leaves are digested more. The size of the vascular bundles still maintain their original shape. As a result, the digestible dry matter of the bamboo plants eaten by giant pandas accounts for only 17%, which is much lower than that of ruminant ungulates (digestibility is often as high as 60%).

The two disadvantages of bamboo's poor nutrition and low digestibility force giant pandas to adopt matching methods. Eating strategy – eat more. In order to survive, giant pandas have to eat large amounts of food non-stop, even at night. Giant pandas spend about 14 hours a day eating bamboo, even in winter, which is why giant pandas do not hibernate. The giant panda, which is "inedible and has no bamboo", can simply be called a "bamboo-eating glutton". Zoo breeding experiments show that an adult giant panda weighs about 15 kilograms of bamboo per day. Through research on the daily food intake of giant pandas in the wild, the daily food intake of adult giant pandas is 10-18 kilograms (fresh weight of bamboo) during the season of eating bamboo leaves and bamboo stalks; and the daily food consumption during the season of eating bamboo shoots is 23-38 kilograms. . Once, a wild giant panda kept eating bamboo shoots, and scientific workers followed quietly to observe. It was found that the giant pandas were eating for 25 of the 48 hours, eating a total of 154.4 kilograms of bamboo shoots! Eat and poop at the same time. I pooped 96 times in 48 hours, and the total weight of the stool was 85 kilograms!

Giant pandas live the life of "hermits in the bamboo forest". Giant pandas are basically not afraid of cold, but they are not tolerant of heat. Their living environment is basically a cool and humid area, usually in cold and humid mountains. Giant pandas are solitary and live a solitary wandering life except during mating and nurturing periods. They determine their territory through the spread of scent and do not allow other giant pandas to intrude without reason. Giant pandas generally move around in the early morning or dusk, and there are no restrictions on their activity areas. They like to move in warm low valley areas in winter, and on slopes and shady slopes in summer. Generally active in dense bamboo forests, it is difficult for people to catch their traces. It can be seen from this that the significance of bamboo to giant pandas is self-evident. This plant can be said to accompany the growth of giant pandas until their death and is indispensable.