The two baby Sumatran tiger cubs, both female, that were born at the San Antonio Zoo in early August have made their Facebook debut.

Pictures of the pair of tiger sisters recently were posted to the San Antonio Zoo's official Facebook page and show a zoo veterinarian examining them with a stethoscope during the cubs' first medical checkup.

The San Antonio cubs' birth came just a day or two before a pair of Sumatran tiger cubs were born Aug. 5 at the Smithsonian National Zoo in Washington, D.C.

Elizabeth Castillo, spokeswoman for the San Antonio Zoo, said the cubs are healthy and weighed 8 pounds each at their checkup. They have yet to be named.

Sumatran tigers are a critically endangered tiger subspecies, according to the World Wildlife Fund. Less than 400 are estimated to exist worldwide.

For weeks, not even members of the zoo staff were allowed to be near the cubs while the mother tiger, Kemala, was acclimating to her new offspring. The father tiger, Raguno, has been kept out of the enclosure where the mother and her cubs are being held.

Dr. Rob Hilsenroff, executive director of the American Association of Zoo Veterinarians, explained why the mother and her cubs have been kept in relative isolation.

“They're not going to risk her rejecting the cubs,” Hilsenroff said from the AAZV offices in northern Florida. “They make behavioral judgments on the mother, and if (the mother) feels the stress of anyone getting closer, anyone other than keepers or anyone they're used to smelling, she'll oftentimes kill the cubs or abandon them.”

Zoos tend to rely on the mother's history with previous litters when making decisions about when to approach the babies and put them on exhibit, but this is Kemala's first litter.

Zoo officials said the public and the media likely wouldn't be seeing the cubs on display at the exhibit until late October or November.

The Facebook pictures are the first ones that clearly show the cubs. Previous photos were grainy images from the monitor outside the tiger enclosure.

Twitter: @sarahtress