The Smithsonian National Zoo posted a video of four lion cubs born Sunday at the zoo to 9-year-old Shera. (Video courtesy Smithsonian National Zoo)

Four new lions were added this week to the population of a city that already has more than its share of the powerful. But don’t expect to see the new lion cubs on exhibit at the Smithsonian’s National Zoo until early summer.

The four lion cubs were born Sunday at the zoo to Shera, a 9-year-old African lioness. The cubs’ delivery took seven hours, ending at 3:17 p.m.

The father is Luke, who has also been named as the father of two female cubs born at the zoo Jan. 24, to a second female lion, Nababiep. For Shera, it is her second litter — and the fifth for 8-year-old father Luke.

Zoo staff watched Shera give birth via a closed-circuit webcam. The first cub was born at 8:27 a.m. and appeared “active and healthy,” according to a press release from the zoo. The other three cubs were born at 9:03 a.m., 11:09 a.m. and at 3:17 p.m.

“All four cubs appear to be nursing, moving and vocalizing well,” the zoo said.

Shera raised her previous four cubs with success, so zoo officials said they are “cautiously optimistic that these cubs will thrive,” according to Kristen Clark, the animal keeper at the Great Cats exhibit at the zoo.

“Like any mom, she needs some peace and quiet to bond with her cubs, so we’re giving her the solitude she needs,” Clark said.

“From what we’ve observed,” she said, “her behaviors are right on point, and there’s no need for us to intervene.”

The zoo said both mothers have space separated from each other and from Luke. But when the time comes, introductions will begin, the zoo said.

“Our aim is to bring all nine lions together,” said animal keeper Rebecca Stites.

In the wild, a lion may take up to six weeks to introduce her cubs to others, so zoo officials said they are following that same process. The zoo’s animal keepers and veterinary team will continue to watch and examine the lion cubs. They will go on exhibit to the public in early summer.

Nababiep and her cubs will remain indoors until late spring. They can be seen on the lion cub camera on the zoo’s Web site. There are two 7-month-old cubs on exhibit at the zoo now — Sumatran tigers Bandar and Sukacita.

The birth of the new cubs is part of the zoo’s effort to build its lion population. The zoo is part of the Association of Zoos and Aquariums’ African Lion Species Survival Plan, which matches animals across the country for breeding.

Zoo officials said the number of African lions in the wild has fallen by 30 percent over the last 20 years as a result of disease, habitat loss and poaching. Lions are considered vulnerable species by the International Union for Conservation of Nature.