Giant panda

Giant panda
Giant panda at the Ocean Park Hong Kong
Conservation status
Vulnerable  (IUCN 3.1)[1]
CITES Appendix I (CITES)[1]
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Ursidae
Genus:	Ailuropoda
Species:	A. melanoleuca
Binomial name
Ailuropoda melanoleuca David, 1869[2]
Subspecies
A. m. melanoleuca A. m. qinlingensis
Giant panda range

The giant panda (Ailuropoda melanoleuca), also known as the panda bear or simply panda, is a bear species endemic to China. It is characterised by its white coat with black patches around the eyes, ears, legs and shoulders. Its body is rotund; adult individuals weigh 100 to 115 kg (220 to 254 lb) and are typically 1.2 to 1.9 m (3 ft 11 in to 6 ft 3 in) long. It is sexually dimorphic, with males being typically 10 to 20% larger than females. A thumb is visible on its forepaw, which helps in holding bamboo in place for feeding. It has large molar teeth and expanded temporal fossa to meet its dietary requirements. It can digest starch and is mostly herbivorous with a diet consisting almost entirely of bamboo and bamboo shoots.

The giant panda lives exclusively in six montane regions in a few Chinese provinces at elevations of up to 3,000 m (9,800 ft). It is solitary and gathers only in mating seasons. It relies on olfactory communication to communicate and uses scent marks as chemical cues and on landmarks like rocks or trees. Females rear cubs for an average of 18 to 24 months. The oldest known giant panda was 38 years old.

As a result of farming, deforestation and infrastructural development, the giant panda has been driven out of the lowland areas where it once lived. The Fourth National Survey (2011–2014), published in 2015, estimated that the wild population of giant pandas aged over 1.5 years (i.e. excluding dependent young) had increased to 1,864 individuals; based on this number, and using the available estimated percentage of cubs in the population (9.6%), the IUCN estimated the total number of Pandas to be approximately 2,060.^[1][3] Since 2016, it has been listed as Vulnerable on the IUCN Red List. In July 2021, Chinese authorities also classified the giant panda as vulnerable. It is a conservation-reliant species. By 2007, the captive population comprised 239 giant pandas in China and another 27 outside the country. It has often served as China's national symbol, appeared on Chinese Gold Panda coins since 1982 and as one of the five Fuwa mascots of the 2008 Summer Olympics held in Beijing.

The word panda was borrowed into English from French, but no conclusive explanation of the origin of the French word panda has been found.^[4] The closest candidate is the Nepali word ponya, possibly referring to the adapted wrist bone of the red panda, which is native to Nepal. In many older sources, the name "panda" or "common panda" refers to the red panda (Ailurus fulgens),^[5] which was described some 40 years earlier and over that period was the only animal known as a panda.^[6] The binomial name Ailuropoda melanoleuca means black and white (melanoleuca) cat-foot (ailuropoda).^[7]

Since the earliest collection of Chinese writings, the Chinese language has given the bear many different names, including mò (貘, ancient Chinese name for giant panda),^[8] huāxióng (花熊; "spotted bear") and zhúxióng (竹熊; "bamboo bear").^[9] The most popular names in China today are dàxióngmāo (大熊貓; lit. 'giant bear cat'), or simply xióngmāo (熊貓; lit. 'bear cat'). As with the word panda in English, xióngmāo (熊貓) was originally used to describe just the red panda, but dàxióngmāo (大熊貓) and xiǎoxióngmāo (小熊猫; lit. 'little bear cat') were coined to differentiate between the species.^[9]

In Taiwan, another popular name for panda is the inverted dàmāoxióng (大貓熊; lit. 'giant cat bear'), though many encyclopedias and dictionaries in Taiwan still use the "bear cat" form as the correct name. Some linguists argue, in this construction, "bear" instead of "cat" is the base noun, making the name more grammatically and logically correct, which have led to the popular choice despite official writings.^[9] This name did not gain its popularity until 1988, when a private zoo in Tainan painted a sun bear black and white and created the Tainan fake panda incident.^[10][11]

For many decades, the precise taxonomic classification of the giant panda was under debate because it shares characteristics with both bears and raccoons.^[12] In 1985, molecular studies indicated that the giant panda is a true bear, part of the family Ursidae.^[13][14] These studies show it diverged about 19 million years ago from the common ancestor of the Ursidae;^[15] it is the most basal member of this family and equidistant from all other extant bear species.^[15][16]

Two subspecies of giant panda have been recognized on the basis of distinct cranial measurements, colour patterns, and population genetics.^[17]

• The nominate subspecies, A. m. melanoleuca, consists of most extant populations of the giant panda. These animals are principally found in Sichuan and display the typical stark black and white contrasting colours.^[18]
• The Qinling panda, A. m. qinlingensis,^[19] is restricted to the Qinling Mountains in Shaanxi at elevations of 1,300–3,000 m (4,300–9,800 ft). The typical black and white pattern of Sichuan giant pandas is replaced with a light brown and white pattern.^[17] The skull of A. m. qinlingensis is smaller than its relatives, and it has larger molars.^[20]

A detailed study of the giant panda's genetic history from 2012 confirms that the separation of the Qinling population occurred about 300,000 years ago, and reveals that the non-Qinling population further diverged into two groups, named the Minshan and the Qionglai-Daxiangling-Xiaoxiangling-Liangshan group respectively, about 2,800 years ago.^[21]

Of the eight extant species in the bear family Ursidae, the giant panda's lineage branched off the earliest.^[22][23]

The giant panda is endemic to China. It is found in small, fragmented populations in six mountainous regions in the country, mainly in Sichuan, and also in neighbouring Shaanxi and Gansu.^[24] Successful habitat preservation has seen a rise in panda numbers, though loss of habitat due to human activities remains its biggest threat. In areas with a high concentration of medium-to-large-sized mammals—such as domestic cattle, a species known to degrade the landscape—the giant panda population is generally low. This is mainly attributed to the panda's avoidance of interspecific competition.^[25][26]

The species has been located at elevations of 2,400 to 3,000 m (7,900 to 9,800 ft) above sea level.^[27] They frequent habitats with a healthy concentration of bamboos, typically old-growth forests, but may also venture into secondary forest habitats.^[28] The Daxiangling Mountain population inhabits both coniferous and broadleaf forests.^[29] Additionally, the Qinling population often selects evergreen broadleaf and conifer forests, while pandas in the Qionglai mountainous region exclusively select upland conifer forests. The remaining two populations, namely those occurring in the Liangshan and Xiaoxiangling mountains, predominantly occur in broadleaf evergreen and conifer forests.^{[13]: 137–148}

Giant pandas once roamed across Southeast Asia from Myanmar to northern Vietnam. Their range in China spanned much of the southeast region. By the Pleistocene, climate change affected panda populations, and the subsequent domination of modern humans led to large-scale habitat loss.^[30][31] In 2001, it was estimated that the range of the giant panda had declined by about 99% of its range in earlier millenniums.^[32]

The skull of a giant panda at the Smithsonian Museum of Natural History

Close-up of giant panda at ZooParc in Beauval, France

The giant panda has a body shape typical of bears. It has black fur on its ears, limbs, shoulders and around the eyes. The rest of the animal's coat is white.^[33] The bear's distinctive coloration appears to serve as camouflage in both winter and summer environments as they do not hibernate. The white areas serve as camouflage in snow, while the black shoulders and legs conceal them in shade.^[34] Studies in the wild have found that when viewed from a distance, the panda displays disruptive coloration, while up close, they rely more on blending in.^[35] The black ears may be used to display aggression,^[34] while the eye patches might facilitate them identifying one another.^[34][36] The giant panda's thick, woolly coat keeps it warm in the cool forests of its habitat.^[33]

The panda's skull shape is typical of durophagous carnivorans. It has evolved from previous ancestors to exhibit larger molars with increased complexity and expanded temporal fossa.^[37][38] A study revealed that a 117.5 kg (259 lb) giant panda had a bite force of 1298.9 Newton (BFQ 151.4) at canine teeth and 1815.9 Newton (BFQ 141.8) at carnassial teeth.^[39] Adults measure around 1.2 to 1.9 m (3 ft 11 in to 6 ft 3 in) long, including a tail of about 10–15 cm (3.9–5.9 in), and 60 to 90 cm (24 to 35 in) tall at the shoulder.^[40][41] Males can weigh up to 160 kg (350 lb).^[42] Females are generally 10–20% smaller than males.^[43] They weigh between 70 kg (150 lb) and 125 kg (276 lb).^[44][40][45] The average weight for adults is 100 to 115 kg (220 to 254 lb).^[46]

The giant panda's paw has a digit similar to a thumb and five fingers; the thumb-like digit – actually a modified sesamoid bone – helps it to hold bamboo while eating.^[47][48] The giant panda's tail, measuring 10 to 15 cm (3.9 to 5.9 in), is the second-longest in the bear family, behind the sloth bear.^[43]

Despite its taxonomic classification as a carnivoran, the giant panda's diet is primarily herbivorous, with approximately 99% of its diet consisting of bamboo.^[49] However, the giant panda still has the digestive system of a carnivore, as well as carnivore-specific genes,^[50] and thus derives little energy and little protein from the consumption of bamboo. The ability to break down cellulose and lignin is very weak, and their main source of nutrients comes from starch and hemicelluloses. The most important part of their bamboo diet is the shoots, that are rich in starch and have up to 32% protein content. Accordingly, pandas have evolved a higher capability to digest starches than strict carnivores.^[51] Raw bamboo is toxic, containing cyanide compounds. Pandas' body tissues are less able than herbivores to detoxify cyanide, but their gut microbiomes are significantly enriched in putative genes coding for enzymes related to cyanide degradation, suggesting that they have cyanide-digesting gut microbes.^[52] It has been estimated that an adult panda absorbs 54.8–66.1 mg (0.846–1.020 gr) of cyanide a day through its diet. To prevent poisoning, they have evolved anti-toxic mechanisms to protect themselves. About 80% of the cyanide is metabolized to less toxic thiocyanate and discharged in urine, while the remaining 20% is detoxified by other minor pathways.^[53]

During the shoot season (April–August), pandas store a large amount of food in preparation for the months succeeding this seasonal period, in which pandas live off a diet of bamboo leaves.^[54] The giant panda is a highly specialised animal with unique adaptations, and has lived in bamboo forests for millions of years.^[55] The average giant panda eats as much as 9 to 14 kg (20 to 31 lb) of bamboo shoots a day to compensate for the limited energy content of its diet. Ingestion of such a large quantity of material is possible and necessary because of the rapid passage of large amounts of indigestible plant material through the short, straight digestive tract.^[56][57] It is also noted, however, that such rapid passage of digesta limits the potential of microbial digestion in the gastrointestinal tract,^[56] limiting alternative forms of digestion. Given this voluminous diet, the giant panda defecates up to 40 times a day.^[58] The limited energy input imposed on it by its diet has affected the panda's behavior. The giant panda tends to limit its social interactions and avoids steeply sloping terrain to limit its energy expenditures.^[59]

Two of the panda's most distinctive features, its large size and round face, are adaptations to its bamboo diet. Anthropologist Russell Ciochon observed: "[much] like the vegetarian gorilla, the low body surface area to body volume [of the giant panda] is indicative of a lower metabolic rate. This lower metabolic rate and a more sedentary lifestyle allows the giant panda to subsist on nutrient poor resources such as bamboo."^[59] The giant panda's round face is the result of powerful jaw muscles, which attach from the top of the head to the jaw.^[59] Large molars crush and grind fibrous plant material.^[60]

The morphological characteristics of extinct relatives of the giant panda suggest that while the ancient giant panda was omnivorous 7 million years ago (mya), it only became herbivorous some 2–2.4 mya with the emergence of A. microta.^[60][61] Genome sequencing of the giant panda suggests that the dietary switch could have initiated from the loss of the sole umami taste receptor, encoded by the genes TAS1R1 and TAS1R3 (also known as T1R1 and T1R3), resulting from two frameshift mutations within the T1R1 exons.^[50] Umami taste corresponds to high levels of glutamate as found in meat and may have thus altered the food choice of the giant panda.^[62] Although the pseudogenisation (conversion into a pseudogene) of the umami taste receptor in Ailuropoda coincides with the dietary switch to herbivory, it is likely a result of, and not the reason for, the dietary change.^[60][50][62] The mutation time for the T1R1 gene in the giant panda is estimated to 4.2 mya^[60] while fossil evidence indicates bamboo consumption in the giant panda species at least 7 mya,^[61] signifying that although complete herbivory occurred around 2 mya, the dietary switch was initiated prior to T1R1 loss-of-function.^[63]

Pandas eat any of 25 bamboo species in the wild, with the most common including Fargesia dracocephala^[63] and Fargesia rufa.^[64] Only a few bamboo species are widespread at the high altitudes pandas now inhabit. Bamboo leaves contain the highest protein levels; stems have less.^[65] Because of the synchronous flowering, death, and regeneration of all bamboo within a species, the giant panda must have at least two different species available in its range to avoid starvation. While primarily herbivorous, the giant panda still retains decidedly ursine teeth and will eat meat, fish, and eggs when available. In captivity, zoos typically maintain the giant panda's bamboo diet, though some will provide specially formulated biscuits or other dietary supplements.^[66]

Pandas will travel between different habitats if they need to, so they can get the nutrients that they need and to balance their diet for reproduction.^[67]

Although adult giant pandas have few natural predators other than humans, young cubs are vulnerable to attacks by snow leopards, yellow-throated martens,^[68] eagles, feral dogs, and the Asian black bear. Sub-adults weighing up to 50 kg (110 lb) may be vulnerable to predation by leopards.^[69]

Giant pandas are sympatric with other large mammals and bamboo feeders, such as the takin (Budorcas taxicolor). The takin and giant panda share a similar ecological niche, and they consume the same resources. When competition for food is fierce, pandas disperse to the outskirts of takin distribution. Other possible competitors include but is not limited to, the Eurasian wild pig (Sus scrofa), Chinese goral (Naemorhedus griseus) and the Asian black bear (Ursus thibetanus). Giant pandas avoid areas with a mid-to-high density of livestock, as they depress the vegetation.^[70] The Tibetan Plateau is the only known area where both giant and red pandas can be found. Although sharing near-identical ecological niches, competition between the two species has rarely been observed. Nearly 50% of their respective distribution overlaps, and successful coexistence is achieved through distinct habitat selection.^[71]

A captive female died from toxoplasmosis, a disease caused by an obligate intracellular parasitic protozoan known as Toxoplasma gondii that infects most warm-blooded animals, including humans.^[72] They are likely susceptible to diseases from Baylisascaris schroederi, a parasitic nematode known to infect giant panda intestines. This nematode species is known to give pandas baylisascariasis, a deadly disease that kills more wild pandas than any other cause.^[73] Additionally, the population is threatened by canine distemper virus (CDV), canine parvovirus, rotavirus, canine adenovirus, and canine coronavirus. Bacteria, such as Clostridium welchii, Proteus mirabilis, Klebsiella pneumoniae, and Escherichia coli, may also be lethal.^[74]

The giant panda is a terrestrial animal and primarily spends its life roaming and feeding in the bamboo forests of the Qinling Mountains and in the hilly province of Sichuan.^[75] Giant pandas are generally solitary.^[55] Each adult has a defined territory and a female is not tolerant of other females in her range. Social encounters occur primarily during the brief breeding season in which pandas in proximity to one another will gather.^[76] After mating, the male leaves the female alone to raise the cub.^[33] Pandas were thought to fall into the crepuscular category, those who are active twice a day, at dawn and dusk; however, pandas may belong to a category all of their own, with activity peaks in the morning, afternoon and midnight. The low nutrition quality of bamboo means pandas need to eat more frequently, and due to their lack of major predators they can be active at any time of the day.^[77] Activity is highest in June and decreases in late summer to autumn with an increase from November through the following March.^[78] Activity is also directly related to the amount of sunlight during colder days.^[78] There is a significant interaction of solar radiation, such that solar radiation has a stronger positive effect on activity levels of panda bears.^[78]

Pandas communicate through vocalisation and scent marking such as clawing trees or spraying urine.^[44] They are able to climb and take shelter in hollow trees or rock crevices, but do not establish permanent dens. For this reason, pandas do not hibernate, which is similar to other subtropical mammals, and will instead move to elevations with warmer temperatures.^[79] Pandas rely primarily on spatial memory rather than visual memory.^[80] Though the panda is often assumed to be docile, it has been known to attack humans on rare occasions.^[81][82][83] Pandas have been known to cover themselves in horse manure to protect themselves against cold temperatures.^[84]

The species communicates foremost through a blatting sound; they achieve peaceful interactions through the emission of this sound. When in oestrus, a female emits a chirp. In hostile confrontations or during fights, the giant panda emits vocalizations such as a roar or growl. On the other hand, squeals typically indicate inferiority and submission in a dispute. Other vocalizations include honks and moans.^[85]

Giant pandas heavily rely on olfactory communication to communicate with one another. Scent marks are used to spread these chemical cues and are placed on landmarks like rocks or trees.^[86] Chemical communication in giant pandas plays many roles in their social situations. Scent marks and odors are used to spread information about sexual status, whether a female is in estrus or not, age, gender, individuality, dominance over territory, and choice of settlement.^[86] Giant pandas communicate by excreting volatile compounds, or scent marks, through the anogenital gland.^[86][87] Giant pandas have unique positions in which they will scent mark. Males deposit scent marks or urine by lifting their hind leg, rubbing their backside, or standing in order to rub the anogenital gland onto a landmark. Females, however, exercise squatting or simply rubbing their genitals onto a landmark.^[86][88]

The season plays a major role in mediating chemical communication.^[89] Depending on the season, mainly whether it is breeding season or not, may influence which odors are prioritized. Chemical signals can have different functions in different seasons. During the non-breeding season, females prefer the odors of other females because reproduction is not their primary motivation. However, during breeding season, odors from the opposite sex will be more attractive.^[89][90] Because they are solitary mammals and their breeding season is so brief, female pandas secrete chemical cues in order to let males know their sexual status.^[90] The chemical cues female pandas secrete can be considered to be pheromones for sexual reproduction.^[90] Females deposit scent marks through their urine which induces an increase in androgen levels in males.^[90] Androgen is a sex hormone found in both males and females; testosterone is the major androgen produced by males. Civetone and decanoic acid are chemicals found in female urine which promote behavioral responses in males; both chemicals are considered giant panda pheromones.^[90] Male pandas also secrete chemical signals that include information about their sexual reproductivity and age, which is beneficial for a female when choosing a mate.^[86][89] For example, age can be useful for a female to determine sexual maturity and sperm quality.^[91] Pandas are also able to determine when the signal was placed, further aiding in the quest to find a potential mate.^[91] However, chemical cues are not just used for communication between males and females, pandas can determine individuality from chemical signals. This allows them to be able to differentiate between a potential partner or someone of the same sex, which could be a potential competitor.^[91]

Chemical cues, or odors, play an important role in how a panda chooses their habitat. Pandas look for odors that tell them not only the identity of another panda, but if they should avoid them or not.^[91] Pandas tend to avoid their species for most of the year, breeding season being the brief time of major interaction.^[91] Chemical signaling allows for avoidance and competition.^[88][89] Pandas whose habitats are in similar locations will collectively leave scent marks in a unique location which is termed "scent stations".^[91] When pandas come across these scent stations, they are able to identify a specific panda and the scope of their habitat. This allows pandas to be able to pursue a potential mate or avoid a potential competitor.^[91]

Pandas can assess an individual's dominance status, including their age and size, via odor cues and may choose to avoid a scent mark if the signaler's competitive ability outweighs their own.^[88] A panda's size can be conveyed through the height of the scent mark.^[88][92] Since larger animals can place higher scent marks, an elevated scent mark advertises a higher competitive ability. Age must also be taken into consideration when assessing a competitor's fighting ability. For example, a mature panda will be larger than a younger, immature panda and possess an advantage during a fight.^[88]

Giant pandas reach sexual maturity between the ages of four and eight, and may be reproductive until age 20.^[93] The mating season is between March and May, when a female goes into estrus, which lasts for two or three days and only occurs once a year.^[94] When mating, the female is in a crouching, head-down position as the male mounts her from behind. Copulation time ranges from 30 seconds to five minutes, but the male may mount her repeatedly to ensure successful fertilisation. The gestation period is somewhere between 95 and 160 days - the variability is due to the fact that the fertilized egg may linger in the reproductive system for a while before implanting on the uterine wall.^[94] Giant pandas give birth to twins in about half of pregnancies.^[95] If twins are born, usually only one survives in the wild. The mother will select the stronger of the cubs, and the weaker cub will die due to starvation. The mother is thought to be unable to produce enough milk for two cubs since she does not store fat.^[96] The father has no part in helping raise the cub.^[33]

When the cub is first born, it is pink, blind, and toothless,^[33] weighing only 90 to 130 g (3.2 to 4.6 oz), or about ⁠1/800⁠ of the mother's weight,^[12] proportionally the smallest baby of any placental mammal.^[97] It nurses from its mother's breast six to 14 times a day for up to 30 minutes at a time. For three to four hours, the mother may leave the den to feed, which leaves the cub defenseless. One to two weeks after birth, the cub's skin turns grey where its hair will eventually become black. Slight pink colour may appear on the cub's fur, as a result of a chemical reaction between the fur and its mother's saliva. A month after birth, the colour pattern of the cub's fur is fully developed. Its fur is very soft and coarsens with age. The cub begins to crawl at 75 to 80 days;^[12] mothers play with their cubs by rolling and wrestling with them. The cubs can eat small quantities of bamboo after six months, though mother's milk remains the primary food source for most of the first year. Giant panda cubs weigh 45 kg (99 lb) at one year and live with their mothers until they are 18 months to two years old. The interval between births in the wild is generally two years.^[98]

Initially, the primary method of breeding giant pandas in captivity was by artificial insemination, as they seemed to lose their interest in mating once they were captured.^[99] This led some scientists to trying methods such as showing them videos of giant pandas mating^[100] and giving the males sildenafil (commonly known as Viagra).^[101] In the 2000s, researchers started having success with captive breeding pro