Sumatran rhinos were once widespread across southern Asia; today, fewer than 100 are believed to be left in the wild.An international captive breeding program was launched in 1984, sending rhinos to the United States and United Kingdom.The first calf wasn’t born until 2001, because maintaining and breeding these rare rhinos turned out to be an unusual challenge. This is Part One of a two-part series about attempts to rescue Sumatran rhinos from the brink of extinction by breeding the critically endangered species in captivity. Read Part Two here. A baby Sumatran rhino displays the species’ characteristic shaggy fur. Photo courtesy of the Cincinnati Zoo. The most endangered rhino is one you’ve probably never heard of. Unlike its more famous African cousins, the Sumatran rhino (Dicerorhinus sumatrensis)–sometimes called the hairy rhinoceros–has two horns and a variable coat of shaggy fur, especially on the ears. They’re smaller, solitary, and live in dense tropical forest. It’s not the first word that comes to mind when you think of rhinos, but if any rhino species is cute, this is the one. Once widespread across Southeast Asia and the Himalayan foothills, hunting and habitat loss reduced Sumatran rhinos to just a few small populations by the end of the 20th century, prompting fears that without intervention the species would go extinct. Husbandry and health In 1984, when perhaps a thousand were estimated to be left in the wild, a program was initiated to take rhinos into captivity from habitat that was about to be destroyed. Forty Sumatran rhinos were captured in Indonesia and Malaysia with the hopes of starting a captive breeding program. Seven of these rhinos were sent to the US, three to the UK and one to Thailand, while seven remained in Indonesia and 22 in Malaysia. By the late 1990s, not only had there been no calves, but fewer than half of those animals were still alive. Some deaths were likely due to old age, but simply maintaining their health in captivity had turned out to be far more difficult than zoos had anticipated. One very basic problem was diet. Many rhinos suffered from digestive problems until their caretakers realized the typical zoo diet for browsing species wasn’t suitable. “A primarily hay-based diet didn’t work,” Terri Roth of the Cincinnati Zoo, who led the research team that produced the first calf, told Mongabay. “With a lot of other browser species we can convert them to another diet in captivity, but these we can’t.” Fresh browse, in particular ficus, was crucial.