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Giant Pandas' Lazy Lifestyle Justified by Science

Relative to their size, giant pandas have a smaller brain, liver and kidneys than other bears and they have extremely low thyroid hormone levels.

Giant pandas have an insatiable hankering for bamboo, but scientists have long wondered how the bears survive on such a fibrous and low-nutrient plant. Now, a new study finds that giant pandas have clever ways to conserve energy, including having lazy lifestyles, small organs and special genes.

The researchers followed five captive and three wild giant pandas (Ailuropoda melanoleuca) for about a year. By using GPS trackers and analyzing chemicals excreted in the pandas' poop, they were able to measure the amount of energy the pandas spent each day. Surprisingly, the pandas expended only about 38 percent of the energy that an animal with the same body mass would require.

"We thought the metabolism of the panda would be low because the bamboo diet contains low energy," said senior author Fuwen Wei, a professor of zoology at the Chinese Academy of Sciences in Beijing. "But it is very surprising that it is this exceptionally low, equal to the three-toed sloth, and much lower than the koala." [Butter Balls: Photos of Playful Pandas]

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The only known mammals that have a lower daily energy usage than the giant panda are the Australian rock rat (Zyzomys argurus), which spends 21 percent of its expected energy per day, and the golden mole (Eremitalpa namibensis), which spends 26 percent of its expected energy per day, the researchers wrote in the study.

However, while it's unknown how the rock rat and golden mole conserve energy, the researchers found several ways that pandas save calories.

For starters, the GPS recordings showed that pandas are a lazy bunch; they don't move a lot, and when they do, they move slowly. Captive pandas spent just a third of their time, and wild pandas about half of their time, moving around, the researchers found. Furthermore, wild pandas forage at an average speed of 50 feet (15.5 meters) an hour, a rate that is "very low," the researchers wrote in the study.

The researchers also reviewed giant panda autopsy data, and found that relative to their size, the animals have a smaller brain, liver and kidneys than other bears. These small organs likely require less energy to function, saving the pandas precious calories, the researchers said.

Finally, the research team looked at the giant panda's thyroid hormones, which regulate metabolism. A hormone sample taken from the captive pandas showed that levels of two thyroid hormones - thyroxine and triiodothyronine - were about half of what is seen in mammals with the same body mass, the researchers found.

In fact, these hormone levels were even lower than those seen in hibernating black bears (Ursus americanus), they said. Interestingly, giant pandas have thyroid hormone levels comparable to the gray seal (Halichoerus grypus), which lowers its metabolism while diving to conserve energy, the researchers said.

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When they examined the giant panda's genome, they found it had an intriguing genetic mutation in the DUOX2 gene, which is involved in thyroid hormone production. In humans, mutations in the DUOX2 gene can lead to underactive thyroids, the researchers said. So, it makes sense that the panda's low levels of thyroxine and triiodothyronine are "probably caused by a genetic mutation in the thyroid hormone," Wei told Live Science.

Taken together, the panda's lazy lifestyle, small organs and thyroid hormones likely help it conserve energy, allowing it to continue munching on its favorite low-nutrient snack: bamboo.

The study was published online today (July 9) in the journal Science.

Original article on Live Science.

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Conservation efforts to protect giant pandas are working so well that they are even benefitting other animals that live alongside the black and white bears in China. The Fourth National Giant Panda Survey, released by the Chinese government last Friday, found that the wild panda population has increased nearly 17 percent over the last decade, with other animals within the giant panda's habitat -- including nature reserves -- also faring better. The giant panda population now consists of an estimated 1,864 individuals, up from 1,596 in 2003. In the wild, giant pandas are only found at China's Sichuan, Shaanxi and Gansu provinces. Camera trap images taken by World Wildlife Fund show that these regions are also rich with other wildlife. "Giant pandas are not only a conservation icon, they are also an umbrella species," Colby Loucks, deputy director of the WWF Wildlife Conservation Program, told Discovery News. "Protecting them means protecting the many rare and endangered species that share their mountainous habitat."

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Big cat predators such as snow leopards prowl around the turf inhabited by giant pandas. They may prey upon giant panda cubs, but a healthy ecosystem keeps both populations in balance. Snow leopards are listed as being endangered by the IUCN Red List of Threatened Species.

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The common goral, also known as the Chinese or grey long-tailed goral, isn't so common anymore. This small, goat-like animal is native to mountainous regions in China and certain other Asian countries. It used to be prevalent, but has been over-hunted in some of its ranges. Protection of giant pandas is helping the situation because it has led to the establishment of nature reserves, which account for 66.8 percent of the total wild population size and 53.8 percent of the total habitat area of giant pandas. Gorals live in these regions too, and therefore gain some protection from hunters.

Several distinctive birds, such as the blood pheasant, were also snapped by WWF camera traps within giant panda protected territories. This bird gets its name, not from any taste for blood, but because of its rich crimson red feathers and bright red skin on parts of its body.

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Conservationists were thrilled to discover that the camera traps snapped this and other images of golden snub-nosed monkeys within giant panda reserves. These monkeys, which inhabit the mountainous forests of Southwestern China, are listed as being endangered. They, along with the other animals on this list, are now benefiting from efforts to save giant pandas.

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Giant pandas share territory with other panda species, such as the red panda. Less than 10,000 of these very furry and colorful small pandas are estimated to exist in the wild. It's hoped that the uptick in the giant panda population and related efforts will help to save red pandas too.

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Camera traps captured an image of this mountain weasel as it scurried over snow-topped rocky terrain in the mountains of China. Its population is doing well now in the region. This likely benefits some of the large birds in the area too, since they are thought to prey upon the agile weasels.

This Chinese monal, a pheasant that inhabits the mountains of central China, looks as though it is taking a selfie. The distant relative of turkeys is listed as being vulnerable, so it is a good sign that the camera traps set up on giant panda turf captured this and other images of the plump birds.

The takin, also known as a gnu goat, can withstand conditions at very high elevations, just as giant pandas can. These stocky mammals are listed as being vulnerable, a status that hopefully will improve over time with continued protection of giant panda lands.

The Asiatic black bear is also known as the "moon bear" because it sports a half moon-resembling patch of white fur on its chest. They are mostly herbivorous, but are not as specialized for plant feasting -- in terms of their anatomy -- as giant pandas are. They are listed as being vulnerable, and therefore need conservation. Ginette Hemley, senior vice president of WWF Wildlife Conservation and her team explained that there appears to be a decline in traditional threats, such as poaching, which have in the past reduced giant panda populations and those of other large mammals, like the Asiatic black bear. The new survey, however, notes that threats posed by large-scale infrastructure projects like mining, hydro-power and work to maintain roads and railroads, are becoming more severe.

The tufted deer gets its name from the prominent tuft of black hair located on its forehead. This small deer, which is a close relative of the muntjac, has a healthy, numerous population within giant panda territories. WWF supports the government of China's work by establishing nature reserves and a conservation network that integrates those reserves with forests, farms, and corridors of woodlands that allow tufted deer, giant pandas and other animals to find food and meet mates.

The camera trap images included this close-up of a giant panda paw, snapped as the black and white bear investigated the camera equipment. It looks a bit like a panda high five, which is appropriate given the good news about more giant pandas and the improving populations of other animals within protected areas. As Loucks concluded, "Amazing wildlife such as the golden monkey, takin, and numerous rare pheasant and salamander species all share space with the giant panda and benefit from their conservation."