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10 things you probably don't know about bears

By: Jaymi Heimbuch on Oct. 20, 2015, 9:36 a.m.
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The tiniest baby of them all

Panda cubs are famous the world over. The giant panda is the poster child for endangered species so it is a very big deal when cubs are born in captivity. The Internet waits with bated breath to see how newborn cubs will fare when they're announced. But there is something just as fascinating about these cubs as their rarity — it's their size.

Aside from marsupials, panda cubs are the smallest newborn mammal relative to the mother's size in the world. They are around 1/900th the size of their mother, and weigh a mere 3 to 5 ounces at birth. Tiny, hairless, blind and essentially immobile, the panda cub is completely helpless and fragile when born.

It seems it would behoove a wild animal to have a slightly more capable infant, so why are panda cubs so small? "The answer has a lot to do with bamboo," reports The Washington Post. The panda's diet is low in nutritional value, which requires a panda to have a low metabolism.

"This low metabolism means the female's blood-oxygen level is relatively low. That tiny panda cub actually has a better shot at survival if it can breathe fully oxygenated air — and so being outside in the world is better than being inside the mother. Moreover, the kind of fatty acids that the cub needs can't be passed from the mother to the cub through the placental barrier," which means being on the outside of the mother and drinking milk rich in fatty acids is necessary to survival.

Because bears are at the top of the food chain, they don't have to worry too much about defending a tiny cub. So, the cub can take its sweet time growing up; a panda cub doesn't open its eyes for six weeks, doesn't start moving around for three months, and doesn't stop nursing for nine months.