Pandas are lazy – for a good reason
Giant pandas take great measures to be lazy, so that they can survive on their favorite bamboo meals, scientists report in a new study.
These cuddly black-and-white bears are usually seen munching on bamboos – if not napping or lazing about. Herbivores, like cows and horses, have specialized digestive tracts that allow them to break down and absorb nutrients from tough plant materials. But pandas, like their meat-eating cousins, have digestive systems of carnivores and are not suited for vegetarian diet.
What if we had to survive on low-calorie foods, like celeries? We could gorge on them whole day, otherwise staying idle. Pandas take idle to an extreme level, according to a team of Chinese and British scientists.
The scientists found that pandas spend about 5 megajoules (MJ), or 1.2 million calories, of energy daily. This is only about 40% of the expected energy expenditure for a mammal based on the body mass. In fact, the scientists say the daily energy expenditure of a panda is even lower than that of a koala (at 69% of the expected), putting the vegetarian bear to the same level as a famed lethargic, three-toed sloth (at 36% of the expected).
The scientists also tracked the movement of pandas by GPS. The bears spent only about half of their time engaged in physical activities, and moved at a sluggish average speed of 27 meters (or 30 yards) per hour.
We spend energy even when we stay still. This is because our body consumes energy to survive – maintaining body temperature and keeping organs busy at work, for example. A hibernating bear minimizes the so-called resting or basal metabolic rate (that is, energy expenditure rate at rest) by lowering its body temperature. Pandas, instead, have reduced sizes of some vital organs (brains, livers, and kidneys) relative to other mammals, demanding less energy, the scientist report.
Pandas also have low thyroid hormone levels, at half of the expected, which helps them to slow the metabolic rate, the scientists found. Thyroid hormones work as metabolic accelerators. Levels of these hormones in pandas are even lower than that of hibernating black bears. The scientists found a mutation unique to pandas in a gene involved in making thyroid hormones, which is likely linked to the pandas’ reduced metabolic rate.
What astonished me the most in the report, though, is that pandas produce up to 5 liters (or 1.3 gallons) of urine every day, spending an estimated 2MJ in the process. That’s whopping 40% of their daily energy expenditure! The scientists attribute the high urination amount to scent marking habit of the pandas.
The study, led by Fuwen Wei at Chinese Academy of Sciences, Beijing, China, is published in this week’s issue of Science.