Ten-year-old Nababiep, an African lion at the National Zoo, gave birth to two live cubs on Friday. (Smithsonian National Zoo)

The National Zoo announced Monday that one of its female African lions delivered two healthy cubs Friday — making a total of nine surviving lion cubs born at zoo in the past four years.

Ten-year-old Nababiep gave birth to three cubs in an eight-hour period. One was stillborn. The cubs are the third litter for Nababiep, and the fourth for the 8-year-old father, Luke.

Two female lions, Shera and Nababiep, and the male, Luke, live at the zoo’s Great Cats exhibit. The zoo said Shera may also be pregnant.

The first cub was born at 3:58 a.m. and appeared active and healthy. Five hours later, at 8:51 a.m., Nababiep delivered the stillborn cub. The third was born at 11:24 a.m. and was healthy.

It is not uncommon for lions to have some healthy cubs and one or more stillborn ones in the same litter, the zoo said.

Nababiep, a lion at the National Zoo, feeds her two cubs that were born Jan. 24. A third cub was stillborn. (Smithsonian's National Zoo)

“The first few days of a lion cub’s life are very fragile,” said Rebecca Stites, an animal keeper at the Great Cats exhibit, according to a zoo statement.

Nababiep’s first cub, born in May 2010, lived only 48 hours. A piece of bedding straw became lodged in one of its lungs, which resulted in pneumonia.

The zoo said the mortality rate for lion cubs in captivity is about 30 percent, compared with 67 percent in the wild.

These are the first lion cubs born at the zoo in four years.

In August 2010, Shera gave birth to four cubs. In September 2010, Nababiep gave birth to three cubs. All have since been sent to breeding programs at other zoos.

This litter will not be on exhibit until late spring, the zoo said, but its lion cub cam was activated Monday afternoon.