Overnight, the Smithsonian’s National Zoo welcomed this year’s second litter of African lion (Panthera leo) cubs. On Aug. 31, Shera gave birth to four cubs—the first litter for 5-year-old Shera and the first surviving litter for 4-year-old male Luke.

“The National Zoo is thrilled that our captive management program for African lions is growing,” said Dennis Kelly, director of the Zoo. “After the sad loss of our other female lion’s cub in May, these cubs symbolize hope for the Zoo and for conservation programs. They will help build healthy, genetically diverse populations and contribute greatly to their species’ survival.”

The cubs were born between 10:30 p.m. Monday and 2:30 a.m. Tuesday and since then have been mobile and appear to have nursed. Because it is not uncommon for intervals between births to be several hours long, keepers will continue to monitor Shera for additional cubs. (A short video clip of the mother and newborn cubs is available on the Zoo’s YouTube page.)

Although the Zoo has managed lions in the past, it has been many years since it had the right combination of animals by age and gender to develop a pride. Doing so successfully has required extensive planning, knowledge of the species’ natural history and an understanding of the individual animals involved.

Introductions among Shera, Luke and Nababiep (Shera’s 6-year-old sister) began almost two years ago in an effort to build a pride. Six months ago, all three lions spent time in the yard together as a group for the first time. The introduction was a positive one, and Shera and Luke bred the second week of May. Over the past few weeks, keepers have gradually separated the three again to give Shera privacy and emulate the natural process. In the wild, lions may wait up to six weeks before introducing their cubs to the rest of the pride. Keepers predict the cubs will not be out in the yard, however, until late fall, which will give the Zoo’s animal keepers and veterinary team time to examine them and monitor Shera as she adjusts to being a first-time mother. She has privacy in her own cubbing den but also has the option of visiting Nababiep through a mesh door.

The birth of lion cubs marks the next step in building a pride, and keepers will slowly introduce the cubs to their aunt with the aim of eventually bringing all seven lions together. Keepers had a similar plan for Nababiep, who gave birth to a single male cub May 18. Unfortunately, a straw seed became lodged in the cub’s lung, and it died of pneumonia.

“Since the unfortunate death of Naba’s cub, we’ve investigated various alternative bedding options,” said Rebecca Stites, a lion and tiger keeper. “The use of bedding is imperative as it protects the cubs from trauma during the first fragile weeks of their lives. We’ve provided Shera and her cubs with shavings and soft hay with as few seed as possible.”

Nearly two weeks after Nababiep was reintroduced to the pride, she bred with Luke again. Keepers suspect that Nababiep is pregnant again and will monitor her behavior in the coming weeks.

The formation of prides makes lions unique among the great cats, many of which are solitary animals. Hunting, disease and habitat loss have contributed to a decline in the population of African lions, which are considered a vulnerable species by the International Union for Conservation of Nature.

“Our hope is that her maternal instincts will kick in quickly, but we are keeping in mind that this whole experience is new to her,” said Kristen Clark, a lion and tiger keeper. “We will be closely monitoring how she reacts to her cubs, since there is a possibility that she could reject them. Naba was an excellent mother to her first cub, and we have every indication that Shera will be the same.”