In fact, if the timing isn't right, the highly endangered animals, which can reach up to 1,800 pounds in weight, tend to get violent not amorous with each other.
"They're very solitary," explains Dr. Terri Roth, director of the Cincinnati Zoo's Center for Research of Endangered Wildlife. "When you put them in close contact, if the female is not receptive, usually the male will chase after the female, there's sometimes biting and it can get pretty hairy."
That's why the eight-month pregnancy of Emi, a, 11-year-old female Sumatran rhino on loan to the Cincinnati Zoo, is hailed as rare reproductive success. Emi has carried five unsuccessful pregnancies before, none of which lasted longer than three months. But this pregnancy is the longest yet and looks to be most promising.
If the baby is carried and successfully delivered after a full 16-month pregnancy, it would be the first Sumatran rhino bred and born in captivity since 1889 in the Calcutta Zoo.
Long Time Trying
"It's an extremely significant event," says Tom Foose, director of the International Rhino Foundation, which helped fund the effort. "We've been trying since the mid-1980s to reproduce this rhino in captivity. The fact that we're now half way through a pregnancy after so many frustrations and failures, is miraculous."
The birth would also help boost prospects for waning populations of the rhino. Only 16 Sumatran rhinos exist in captivity and less than 300 remain in the wild. Roth hopes that trainers at rhino sanctuaries in Malaysia and Indonesia might be able to apply what the Cincinnati team learned to help encourage more births.
"Clearly this single calf won't save the species," says Roth. "But what we learn may help in our collaborative work with conservationists in Malaysia and Indonesia."
Over the last 10 years wild populations of the Sumatran rhino, also known as the hairy rhino for its long, shaggy hair, have declined from rain forests of Malaysia and Indonesia by more than 60 percent. Most of the decline is due to poachers who hunt the solitary animals for their prized two horns.
The Sumatran is one of five known remaining species of the rhinoceroses, which experts believe have existed on Earth for more than 60 million years. Although it isn't the most rare, it is considered the most endangered since its numbers have declined most rapidly in recent years.
Other remaining species of rhino, including the black and white rhinos, are known to reproduce more successfully in captivity. Besides being less than cuddly, the two-horned Sumatran rhino has also proven difficult to mate because females do not start to ovulate until they have mated. And once they begin estrous, they reveal no outward signs.
Rough Rhino Sex
To pinpoint when Emi was ready for mating, Roth used ultrasound technology to monitor the size of her ovaries. Roth's team also followed her hormone levels on a daily basis. When Emi's ovaries reached peak shapes and her hormone levels dipped, Roth introduced a 1,600-pound male Sumatran rhino, Ipuh, into the 18,000-pound female rhino's pen.
"We weren't always correct," says Roth. "There were times when I've put them together a day early and they end up chasing each other."
Even when the timing is right, the result is not always peaceful. As Foose says, "Rhino sex is always very rough and their courtship is rough. But if the female is in estrous it usually is kept under control and directed to productive ends."
Once Roth discovered Emi's pregnancy at day 16, the female rhino was immediately administered a daily dose of progesterone in the form of a liquid squirted on a piece of bread to ensure her pregnancy's success.
Ipuh arrived at the Cincinnati Zoo in 1991, on loan from the Indonesia government, and Emi is on loan from the Los Angeles Zoo. Emi and Ipuh have managed 23 matings since their first introduction in 1997. If this pregnancy proves successful, Roth hopes to continue the courtship and keep both parents at the Cincinnati facility.
Although the process of mating Emi was extremely frustrating and involved, Roth reports her team couldn't have had a more cooperative subject than Emi as long as she was fed.
"If we just kept feeding her fruit, she'd let us do whatever we wanted," says Roth. "She's a very docile animal, so we're hoping that will help the success of her pregnancy."