FRONT ROYAL, Va. (WUSA) -- The story of a possible panda pregnancy at the National Zoo is one that Washingtonians love and anyone who follows it knows why it's a big deal: Pandas are fertile for just 24 hours once a year.
Pandas aren't the only focus when it comes to animal reproduction at the National Zoo. At the Smithsonian Conservation Biological Institute, where more than 4,000 acres of land is dedicated to preserving endangered species, biologists are learning what it takes to successfully reproduce animals that aren't breeding in captivity.
"Around 60% of all animals that you see in zoos these days are considered non-sustainable," said Budhan Pukazhenthi, BVSc, Ph.D., DVM. "There's no guarantee you'll see these animals in the zoo in 50 to 100 years because either the animals are getting old and there's not much reproduction or there are no new genes being brought into the population."
One of the rarest species that zoo-keepers are hand-rearing in Front Royal are the clouded leopard cubs. There are three young cubs at the facility. A litter of two cubs, one male and one female, was born on March 28 and a single female cub was born on May 13.
"We have been very successful in producing cubs on a regular basis," said Pukazhenthi. "And the strategy seems to be putting prepubertal animals - a few months old - male and a female together so that they grow up together. There's no aggression and they breed well. If you put unknown unrelated strangers male and a female together to breed, typically what happens is the male ends up killing the female."
When the cubs are born, they are hand-reared, which also seems to contribute to successful reintegration into zoo facilities. 9NEWS NOW was able to film zoo-keeper Ken Lang feed the baby girl born in May.
"We usually start up with two people normally male and female so the cubs don't become imprinted on either sex or a person and then after they are eating well, we start introducing a new person every week," said Lang.
Imprinting is one concern researchers keep in mind. REcently, it became a huge problem for another endangered animal - a white-naped crane called Walnut.
"Walnut has a behavioral problem she came to us she was over 20 years of age," explained Warren Lynch, the Bird Unit Manager. "She was the single most valuable white nape crane in the population. She had never reproduced. Since she was hand raised by people, she did not recognize that she was a crane."
By the time she came to the Smithsonian, she had been to three other zoos.
"The other three facilities actually tried pairing her with prospective mates and she would always fight with them and even killed two," said Lynch.
Now she has laid three fertile eggs and is considered a success story, one of many researchers hope to share in the years to come.