Six weeks after giant panda Mei Xiang gave birth in Washington, D.C., Smithsonian’s National Zoo revealed the gender of the newborn cub—not with a colored cake or fireworks, but with an adorable photo and the results of a genetic test. It’s a boy!
The genetic testing was conducted at the still-unnamed newborn’s first veterinary exam in September, a full month after its birth on August 21. Genetic tests are the only way to discern the sex of a panda cub in the earliest weeks of its life. Not only are mothers incredibly protective of the cubs at this age, but pandas are also born without genitalia.
That’s not all they’re missing at birth. Newborn giant pandas are almost completely unrecognizable. Rather than sporting their iconic black-and-white markings, pandas emerge from their mothers as pink, wrinkly, blind, squealing creatures roughly the size of a stick of butter. So how do they grow into the cuddly furballs that humans are hardwired to love? Here’s a look at how baby pandas grow up.
Pandas are born fragile and underdeveloped. Weighing between three and five ounces, newborn pandas are 1/900th the weight of their mother. This places them among the smallest newborns compared to their mother of any mammal: Human mothers are only about 20 times heavier than their babies, and killer whales are 50 times heavier. Only marsupials emerge smaller‚ and that’s because their babies get to hole up in their mothers’ pouches to finish developing. Red kangaroos, for example, are born at 1/100,000th the weight of their mothers.
Researchers don’t know for sure why pandas are born so tiny. In December 2019, a study published in the Journal of Anatomy examined the skeletal structures of giant pandas and their bear cousins, which also tend to be born small relative to their mothers. The study found that other bear species gestate for two months and are born with mature skeletons, while newborn pandas gestate for only a month and their skeletons emerge comparatively “undercooked,” according to the study’s authors.
The short gestation likely has to do with the bamboo that makes up most of the bear’s diet, says Laurie Thompson, assistant curator of giant pandas at the National Zoo. Bamboo doesn’t have many nutrients. Rather than expend the enormous amounts of energy needed to grow a fetus, female pandas can focus on developing the high-fat milk that will help their cubs grow outside of the womb.
Panda newborns rely on their mother for milk and protection because they cannot see, hear, or crawl. They are so helpless that they can’t regulate their body temperatures or even excrete waste on their own in the first weeks of life. Instead, the mother has to take care of both, cradling her cubs to keep them warm and rubbing their bellies to stimulate the muscles to release urine and feces. In these early weeks, panda mothers don’t leave their cubs, even when they need to eat or drink.
Motherhood is such a demanding job that pandas who give birth to twins can often only take care of one—and are forced to abandon the other. In captivity, scientists step in to care for the neglected cub and even attempt to swap the cubs to ensure both get their mother’s attention and milk.
Though they don’t develop much inside the womb, panda newborns make up for it quickly. Within 48 hours, white fur begins covering their pink skin, followed by the black markings around their eyes and on their bodies. Within about three weeks, their fur is all filled in.
Newborn pandas also gain weight at a rapid pace, suckling their mother’s milk up to 14 times a day.
“Once they’re out and they’ve got mom taking care of them and feeding them so much, they do start to grow really fast,” Thompson says. Mei Xiang’s newborn gained about 50 percent of its bodyweight between its first two weigh-ins, which took place less than a week apart.
After about a month of holding their babies all day every day, mothers start to experiment with putting their cubs on the ground and leaving the den briefly for food and water breaks.
“As she starts to leave more, you know that the cub is able to regulate its body temperature and is okay with being alone for periods of time,” Thompson says.
At six weeks, they start to open their eyes, and by two months, their ear canals are open. Their squeals deepen into grunts. Finally, around three or four months old, their external genitalia begins to develop, and pandas can finally defecate and urinate on their own. They start to crawl, grow teeth, and may even begin to mouth bamboo—signaling that these cubs are ready for the next phase of life. (These are the joys of watching a panda grow up.)
Pandas start to gain independence from their mothers at about five months old. They leave their dens for the first time and learn how to walk, climb, and eat solid foods. The next year of their lives is all about stretching toward adulthood.
At five months, Thompson says, a panda cub has developed cognitively to the point where keepers can begin the training that will allow them to vaccinate the cub, conduct full health examinations (including drawing blood), and ultimately prepare the cub for the journey it will take to China when it is four years old. As part of the zoo’s cooperative breeding agreement with China, all cubs born at the National Zoo move to China where they enter a breeding program at the China Conservation and Research Center for the Giant Panda. Trainings starts off fairly basic, such as offering cooked sweet potato to encourage the cub to touch its nose to a target. (Learn what happens when pandas are released into the wild.)
Once vaccinated, the panda cub can go outside with its mother where it discovers things squirrels and trees and grass for the first time. Soon, it’ll be climbing trees on its own—an important behavior in the wild to keep the cub safe while its mother goes looking for food. “They learn what they need to do pretty early,” Thompson says.
Although the cub is still reliant on its mother’s milk at six months, it’ll also start eating bamboo and other foods. By its first birthday, though, a panda cub can weigh as much as 75 pounds and will be mostly weaned—though it may continue nursing another six months just for comfort.
Finally, at about one-and-a-half or two years old, the panda is ready to be separated from its mother. Though it’s still growing—and ultimately will grow to up to 300 pounds—Thompson says not much else changes until it becomes sexually mature, at ages four for females and six for males. “They’re pretty much good to go,” she says.
Though Mei Xiang’s newborn cub at 3.6 pounds has quite a bit of growing left to do, the National Zoo is compiling a list of possible baby names, and the keepers say they are looking forward to seeing him start moving around a lot more in the weeks ahead. “It’s certainly a fun time for us,” Thompson says.