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Sun Bears: Latest Developments

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.

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Sun Bear Cubs: 10 months old

Pagi and Cutie at home up high.

Pagi (on top) and Palu at home up high.

Our feisty sun bear twins Palu and Pagi turned 10 months old on August 25. They have come a long way from their squawking, demanding, den-dwelling days. Now I very rarely hear any vocalizations from the cubs, and they demand little of their mother’s time and attention compared to their early days (see post, Sun Bears: Have It Your Way).

Pagi looks up...

Pagi looks up...

They remain largely unmotivated by supplemental food, as they still acquire many of their calories via maternal milk. Though nursing is rarely seen, the cubs’ behavior, coupled with Marcella’s obviously distended mammaries, indicate this is still a primary feeding method for the youngsters. Occasionally, I do see Marcella push a cub away when it tries to suckle, usually at a time when she is most interested in searching for her breakfast in the exhibit.

...and down!

...and down!

When they are not sleeping, the cubs routinely engage in vigorous bouts of social play with each other. Palu, who is about 4 kilograms (8.8 pounds) larger than his sister, can be very physical in these play bouts. He tackles Pagi and paws at her wildly. Despite her smaller size, Pagi seems to set the tone for their play, often terminating the bouts when they get too rough. She loves to initiate bouts of “chase and flee” as she runs from her brother.

Palu takes the upper hand.

Palu takes the upper hand.

It will be interesting to look at the data we have collected thus far and see what behavioral differences there are between young males and females. Our dataset currently includes two males and two females, two twins and two singletons. We know there are some differences in maternal behavior when comparing male cubs to female cubs in giant pandas, but such differences have yet to be explored in the sun bear.

Palu and Pagi are on exhibit every afternoon. Come enjoy them, along with Marcella, while they still retain their youthful exuberance!

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

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Sun Bear Cubs: Snips, Snails, Sugar, and Spice

We were able to pull the sun bear cubs this morning to have the veterinarians examine them. We are happy to announce that Marcella has both a boy and a girl in this litter! Staff had suspected this for some time but needed to wait for confirmation from our veterinarians to be certain. (See previous blog, Wider World for Sun Bear Cubs.)

Now three months old, our little bears are doing very well. Their exploration has gotten bolder, and now they frequently make trips out of the den to play in the adjoining bedrooms. Sometimes, Marcella brings them out when she leaves the den. Other times, they tumble out under their own power. They can walk quite efficiently and are able to climb atop low objects such as the drinker or a small log in the bedroom. Negotiating the steps back up to the den, however, is still a challenge: Marcella usually has to assist when the cubs are ready to go back to their home base. The little girl, especially, seems to know when she needs her nap; she has been seen heading back to the den all alone to find her comfortable place to rest.

Both cubs appear to have robust personalities. The male, it turns out, was the infant we have been hearing with the louder voice, more likely to be crying out to mom in the den. The female has the softer voice and was more calm and restful in the den. All along, the male cub appeared larger than the female, a finding confirmed when we began to weigh them a few weeks ago. One might expect that the larger, louder cub would turn out to be bolder, but so far the little girl seems able to hold her own with her sibling. She solicits play from him, growls at him when she has had enough, and has a mind of her own.

The cubs were first weighed at 73 days of age: the male weighed 11.3 pounds (5.15 kilograms) and the girl weighed 9.13 pounds (4.14 kilograms). This is an earlier weigh-in than our other two sun bear cubs. Bulan’s first weight (see blog, A Sun Bear Boy!) was taken on day 82 (10.76 pounds or 4.88 kilograms), and Danum (see blog, A Comparative Approach) wasn’t weighed until day 142 (21.8 pounds or 9.9 kilograms). Interestingly, despite the fact that they are twins, both current cubs are quite large. Even our smaller female is likely to have been at least as large as Bulan if she had been measured on day 73. Marcella is clearly producing some high-quality milk!

But, alas, as good as that milk might be, the grass is always greener on the other side. This week, keepers have reported seeing the cubs mouthing Marcella’s kibble. Soon, they will be stealing her veggies and treats, and she will compete for food with her babies. I have been surprised that in the past, Marcella doesn’t fight her youngsters for her food while they are young. She usually concedes an item a cub has claimed. Not until the cub is more than a year of age does she typically take her food back from a rambunctious cub. Staff is always monitoring to determine if a dietary modification is necessary, and once the twins are eating solids routinely, we will have to ensure that Marcella is getting plenty, too.

There is a lot of development still ahead for these youngsters before they are capable enough to be safe on exhibit. Climbing the high perches and navigating some of the steep slopes of the exhibit require more skill than these babies currently have. Look for them to make their debut in a few months, when staff is convinced they are ready for that challenge.

Suzanne Hall is a senior research technician for the San Diego Zoo.

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Wider World for Sun Bear Cubs

Things continue to go well in the den for sun bear Marcella and her twin cubs (see previous blog, Sun Bears: Growing Up Great). The youngsters are now nearly 2.5 months old and have grown by literal leaps and bounds. Their eyes have long since fully opened, and the cubs are able to take in the world around them. Now that they are becoming more mobile, they are able to interact with that world as well.

Two weeks ago I recorded the cubs crawling about on the den floor. They dragged their bellies as they pushed with their feet, not always moving about in a straight line. Often the early attempts at crawling resulted in a cub flipping over onto its back unceremoniously, squawking and squirming as it tried to right itself. Last week, I saw some of their first clumsy steps with their bellies held up off the floor. They stumbled and fumbled about, tripping over each other and the nesting material in the den. This week – look out! They are moving quickly around the den and clearing a full adult body length of distance in mere seconds.

Along with this burgeoning motor development comes rapid cognitive leaps. Last week I saw the first signs of social play from the cubs. One would paw or bite at its mother or sibling, and at times Marcella would respond with very gentle nipping or nudging. Today I witnessed the cubs playing with each other for a few moments before getting distracted by other things in their environment. But what could be more enticing than a playmate?

The mouth of the den, that’s what! Beyond the entrance to the dark, warm cave they have always called home lay the big wide world, and the bright lights and noises coming from the mouth of the den are calling to the cubs. Today, they kept wandering to the den opening, standing at the threshold, peering about the adjoining bedroom. Marcella, for her part, isn’t ready for her babies to be so grown up: she repeatedly pulled them back from the den entrance and into the dark recesses of their shelter. As soon as she let go, they would race back to the mouth and stare out. Again and again she pulled them back as they howled and squawked their protests. Finally, she enticed them with a nursing session and they fell asleep against her warm body.

You dodged the bullet this time, Marcella, but the cubs won’t let you get away with it for long. Soon these babies will be charging about the bedrooms and stealing your food. With any luck they will enjoying playing with each other more than tormenting you with their firm bites to your toes and ears.

Suzanne Hall is a senior research techinican at the San Diego Zoo.