A new study found that pandas can be comparable to slow-moving moths in terms of their sluggish movements. According to researchers, this characteristic is said to be attributed to the large-sized animals due to their slower metabolisms, organ size and levels of thyroid hormones. Pandas possess a digestive tract that is highly-adaptive to a meat based diet as evidenced by their carnivorous ancestors. However, their current specialized diet mainly consisting of bamboo, may also be factor contributing to their low energy expenditure.

The researchers led by biologist Fuwen Wei of the Chinese Academy of Sciences' Institute of Zoology in Beijing measured the daily energy consumption of three wild pandas from Foping Nature Reserve in Shaanxi province and five captive pandas from the Beijing Zoo.

The findings of the study published in the journal Science show that the average daily energy expenditure of the wild and captive pandas is 5.2 megajoules, which is only about 38 percent of the expected rate. As for the mean value derived from the investigation of wild pandas, the researchers found that the animals expended 6.2 megajoules per day, which can be translated to approximately 45 percent of the expected number for these animals. More specifically, the experts were able to quantify that the wild pandas spend more than 50 percent of the day resting and that these animals travel at a speed of about 65 feet per hour.

The pandas' thyroid hormone levels were also investigated in the study. The experts determined a gene variation in pandas that matched that of humans with low-functioning thyroids. The researchers found that pandas possess only a fraction of the total normal value of thyroid hormones in mammals, and that the values they exhibited are tantamount to that of a black bear going through hibernation. Because the thyroid gland is responsible for controlling the metabolic mechanisms of the body, the low metabolism observed in pandas may be attributed to their minimal thyroid hormone levels, which is probably due to a mutation in the DUOX2 gene.

"Giant pandas achieved this low metabolism through a suite of morphological, behavioral, physiological and genetic adaptations during their long evolutionary history," says Fuwen Wei, lead author and biologist from the Chinese Academy of Sciences' Institute of Zoology in Beijing.

The researchers were also able to identify that the organs of pandas, particularly its liver, brain and kidneys are relatively small compared to other bear species. This may be partly responsible for the minimal energy demands of the pandas thus their survival with diet mainly consisting of bamboo.

Due to the slow metabolism exhibited by pandas, their coat is an especially important thermoregulatory mechanism to keep them warm because it enables them to retain body heat more efficiently. As per the World Wildlife Fund and Chinese government records, there are approximately 1,800 pandas settling in the wild.