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.