Shera nurses her cubs after giving birth Sunday. The lion also had a litter of four in 2010. (Smithsonian's National Zoo)

The National Zoo’s African lions nearly doubled in number this week, as 9-year-old Shera gave birth to four cubs.

The first cub appeared at around 8:30 a.m. Sunday and the last arrived at 3:17 p.m. All four appear to be nursing, moving around and making noises, zoo officials said.

“Shera successfully raised her previous litter of four in 2010, so we’re cautiously optimistic that these cubs will thrive,” animal keeper Kristen Clark said in a statement.

Zookeepers observed the birth on private webcams and did not get involved, officials said.

Luke, 8, is dad to the cubs as well as to two female cubs born to Shera’s sister Nababiep on January 24.

Zookeepers plan to introduce the two litters to each other this spring. For now, they are in separate dens with their mothers.

Shera’s cubs are expected to be on view to the public in early summer, and Nababiep’s in late spring.

— Christina Barron