Three Lion Cubs - One Stillborn - Delivered at National Zoo in DC [VIDEO]

Two healhty lion cubs were born at the National Zoo in Washington, D.C., the zoo announced Monday.

During an eight-hour labor, Nababiep, the zoo's 10-year-old lioness, gave birth to a litter of cubs on Jan. 24. The litter was the first arrival of African lion cubs at the zoo in four years. Three cubs were born Friday, but one was stillborn, the zoo said.

Zoo officials watched Nababiep give birth via closed-circuit webcam, observing the first cub being born at 3:58 a.m. That cub appeared active and healthy. About five hours later a second cub was delivered, but it was stillborn. The third cub was born just before noon and was active and healthy, the zoo said, adding that is not uncommon for a lion to have one or more stillborn cubs in a litter.

The two living cubs are under close observation by animal care experts at the zoo. So far keepers have not needed to intervene on the mother and her new cubs because they appear to be nursing, moving and vocalizing well, the zoo said.

These cubs are the third litter for Nababiep and the fourth for 8-year-old father, Luke, the zoo said.

Cllick here to see a live webcam of the lion cubs.

The first few days of a lion cub's life are very fragile, and the mortality rate for captive-bred lion cubs less than one year old is 30 percent (compared to 67 percent in the wild), the zoo said. In May 2010, Nababiep, known amongst zookeepers as "Naba," gave birth to a cub that only lived 48 hours, the zoo said. However, keepers are "cautiously optimistic that the [new] cubs will thrive."

"Naba continues to prove that she has great maternal instincts, so the best course of action is for us to allow her to care for and bond with her cubs. We have every indication that she will successfully raise these cubs just as she did her previous litter," said Rebecca Stites, an animal keeper at the zoo's Great Cats exhibit.

About one month after breeding with Nababiep, the cubs' father, Luke, was also bred with Nababiep's younger sister Shera as part of a planned breeding program. It is expected that Shera is pregnant as well.

"One of the best parts of this job is seeing all of our planning and preparation come to fruition," said Kristen Clark, an animal keeper at the Great Cats exhibit. "In 2010, we had a remarkable opportunity to watch seven cubs grow, master husbandry training and go on to other zoos to contribute to their breeding programs. To watch this litter follow in their siblings' footsteps will be incredibly exciting and rewarding."

The newborn lion cubs will remain out of public display until later this year.