Sun Bears: Latest Developments

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Siblings Palu, left, and Pagi

Our sun bear twins are approaching 14 months of age. They have been growing like weeds, both with respect to body size and behavioral development (see post Sun Bear Cubs: 10 Months Old). On many days, when I get to their exhibit, I have to stop and watch a moment before I can identify Palu, our male. He’s a big boy now, weighing only about 11 pounds (5 kilograms) less than his mother, Marcella. He stands nearly as tall as her, and his broad head has taken on the wrinkled, shar pei-like appearance of many of the adult bears. This makes it difficult to immediately distinguish him from his mother. I have to look for her distended mammaries, or his clumsy gate, or a side view (he isn’t as long from head to tail) if the obvious is out of view. It’s amazing to me how quickly he has grown.

Our little girl, Pagi, is growing well, too, but she isn’t as big as her brother. Her head is smooth and not as broad, so she retains the appearance of a juvenile. She reminds me of a puppy, which shouldn’t surprise me: one nickname of this species is “the dog-faced bear.” When you look at Pagi, you can see why.

Pagi and Palu are still great entertainment for each other, but there are plenty of times when the cubs ignore each other and do their own thing. Often Pagi is the quick one, exploring nooks and crannies purposefully after being released to the exhibit. She finds food items rapidly, running up and down the exhibit climbing structures to check the spots where snacks are routinely placed. She doesn’t bother with a thorough search of the exhibit; when the obvious areas are fished out, she moves on to better things. Usually, this means she is the first one to the choice resting spot high up on the left-hand side of the climbing structure, the one each of the bears prefers above all others. It seems to me that Pagi rushes through her breakfast search because she has an eye toward getting that favored napping perch.

By the way, resting high in a tree isn’t unusual for a sun bear. In fact, they are known to be the most arboreal of all bear species. Unlike the panda, which typically takes to the trees only as a youngster, sun bears live high above the ground throughout their lives. This is in part due to their dietary preferences, as the fruit that they eat is usually found high in the branches. It is also a security feature, as the area where sun bears live is inhabited by many dangerous creatures such as snakes and, in some area, big cats. The bears are even known to make night nests in the branches, not unlike another forest dweller in their area, the orangutan. Tree life suits them just fine.

Palu is different from Pagi. He takes his time, wandering about the exhibit more sedately. He is in no hurry. He gets distracted by interesting scents, or new-fallen leaves, or neat enrichment items. By the time he finishes his snack hunt, Pagi is often asleep. Sometimes he climbs up beside her and tries to entice her into play. Sometimes he tries to shove her out of the way to take that choice sleeping spot for himself. Usually, he isn’t successful in this. If he is tired, he may rest there beside his sister, but more and more I see him climb down the structure and curl up alone in a little nook near the bottom of his exhibit. He seems content to separate himself from his mother and his sibling. I don’t recall any of our previous cubs doing this, so I wonder: is this just his personality, more independent than some of the others? Or is this a male thing, to begin to separate himself from social contact at times?

Our previous male cub, Danum, Marcella’s first born, was very attached to his mother, and up until weaning was often seen close to her. Perhaps by virtue of the fact that Palu is a twin, and has relied heavily on his sister for social interaction, he isn’t as demanding of his mother as a result. Danum had only Mom to play with or be close to, but Palu has two options for company and so may feel more secure overall. Or perhaps he is just a more independent little personality than his big brother was.

I still see nursing bouts occasionally and expect the cubs are nursing about twice every 24 hours. I have also seen several attempts at nursing by one of the youngsters that Marcella rejects. Usually a simple postural change is all that is needed to thwart their efforts, and often she simply walks away. A persistent cub can expect a growly bark and a little lunge from Mom, especially if she is trying to get her beauty rest when the cub pounces on her. In some ways, Marcella’s evolution as a mother has mirrored that of our giant panda Bai Yun in that over time she has learned to take care of herself in the process of rearing her young. She has raised this secure, feisty, healthy pair of cubs but continues to look out for number one as well.

Suzanne Hall is a senior research technician for the San Diego Zoo’s Institute for Conservation Research.