Pandas start out as very tiny, helpless individuals, unable to thermoregulate on their own. Their eyes and ears are sealed closed. Because they only grew in utero for about 50 days, many of the cub’s biological systems are not fully developed at the time of birth, and the cub needs many weeks of postpartum growth before it can see, hear, and thermoregulate. A panda cub would die without the diligent care of its mother, and her behavior is finely tuned by millions of years of evolution to ensure the survival of her young. It may look like love, but to a bear, a mother’s behavior pattern is more simply defined as a necessity.
The cubs grow rapidly. Xiao Liwu, so far the smallest of our six cubs, has increased his body weight approximately 25-fold in his first 175 days. Small as he is, he far outpaces human growth patterns, in which the average infant increases its body weight by only about 3-fold in the same time period. Body weight is not the only area in which a human comparison doesn’t hold: his physical development has also proceeded well along a bear-typical pattern. At less than six months of age, Xiao Liwu can fully explore his exhibit. He can climb to the bottom of the moat or the top of the den structure. Soon, he’ll be scaling the heights of the trees in his space.
To endure these climbs, pandas must be capable of falling and shaking it off; I’ve seen youngsters fall from the top of 40-foot trees in the enclosures of China’s Wolong Breeding Base, only to bounce, roll, and shake it off. Our trees don’t approach that height, and Xiao Liwu will be able to withstand a fall from them with little repercussion. He won’t be the first of our cubs to bounce.
As Liwu has grown, his relationship with his mother has changed. He no longer needs her regular attention, as his fur and body fat afford him the protection from the elements he needs to deal with cold or damp. He no longer feeds every two to three hours, so his mother need not worry about providing him access to her mammary glands so frequently. Even so, this growing baby needs an increasing quantity of milk each day, as his body and brain need fuel to develop. Bai Yun must meet his growing nutritional requirements while attending to her own. At this time, Liwu is focused on exploring his new, interesting life outside the den, and Bai Yun is focused on eating for two.
In the wild, a panda mother who did not take seriously the need to consume copious amounts of bamboo would risk the life of her cub and perhaps herself. Bai Yun is not in the wild, of course, but her behavior is constrained by her evolutionary past, and she takes her feeding time seriously. Do not be alarmed if you see her resist the cub’s attempts at social play while she feeds, or if she blocks him from access to her food. It is her job to eat. If he is getting in the way of her getting her job done, she will let him know. It may appear to the human eye that Bai Yun is being stubborn or unkind, but to a bear, she is just taking care of business.
Bai Yun does make time for play with her offspring. Social play with pandas, and with all bears, can look quite rough. These animals are equipped with claws and teeth that appear menacing when exposed. But exposure of teeth does not mean Bai Yun is growling at her cub (she has, not once in her years in San Diego, ever been noted to growl outside of a social encounter with an adult male). It is simply her version of a “play face,” a well-documented aspect of social play among mammals. It looks intimidating because we are human, and we are interpreting her behavior through a human lens. But Liwu is better able to read her play signals. What’s more, please recall that the Panda Cam offers no opportunity for you to hear the play sessions. What you don’t know is: play bouts are typically silent. No squalling or complaining from the cub means he is content with the play session. Bai Yun is not hurting him; he is instead getting something positive out of that interaction. Reading the signs through a bear lens lends itself to a different interpretation of this play than a human lens can provide.
Bai Yun has raised five cubs to the sub-adult stage with great success; all indications are that Liwu is on a healthy trajectory as well. We have no indication—not one—that this cub is not thriving. His weight, like some of his siblings, has plateaued at points. Yet the overall weight trajectory is on the increase. His behavioral development is strong, even advanced when compared with some of his siblings (Yun Zi comes to mind). He is content and relaxed. And Bai Yun is in excellent condition, maintaining a weight above 100 kilograms. Everything suggests that things are going well for Liwu and his mother. Reading the signs through a bear lens, our staff couldn’t be more pleased with our pandas’ progress.
Suzanne Hall is a senior research technician for the San Diego Zoo Institute for Conservation Research. Read her previous post, Big Changes for Little Bears.