Panda cubs.

You’ve probably heard by now that the panda cub that was born in the National Zoo last week has died.  Panda cubs have low survival rates both in captivity and in the wild. The little panda seems to have died from liver failure. From the New York Times:

Zoo patrons had expressed concern that the cub’s 217-pound mother had crushed the baby, who weighed just four ounces — as little as a stick of butter — in her arms. But the necropsy found no outward signs of trauma or infection, the zoo’s chief veterinarian, Dr. Suzan Murray, said at a news conference.

The cub’s liver, which was roughly the size of a lima bean, was hard to the touch in several spots, Dr. Murray said. Also worrisome, she said, were small amounts of liquid in the panda’s abdomen. The liquid itself was not thought to be enough to cause death, Dr. Murray said, but could be a sign of liver malfunction.

One of the challenges in breeding pandas, as well as many other critically endangered species, is that little is known about either their behavior or specific biology in the wild. Consequently zoos have very few markers to refer to in establishing what, say, a normal liver of a one-week-old panda might look like.