The Zoo began 2010 with three lions, and today we have ten. That leonine leap reflects animal instinct and deft human handling.
By Lindsay Renick Mayer
In a small den at the Smithsonian’s National Zoo, seven African lion cubs are asleep in a pile—carelessly nestled on top of one another, limbs sprawled at all angles. One of the cubs occasionally wakes with the aim of taking a nip out of his sister’s tail, but gives up before falling back into a deep slumber.
Through the Zoo’s live lion cub cams, Internet users around the globe are peering into this world, glimpsing sights once reserved to keepers and veterinarians. What is missing from this vantage point, though, is the extensive behind-the-scenes work that went into these heralded births. The seven healthy cubs are the result of years of extensive research, consultation, and observation; careful hormone monitoring; and continuous world-class veterinary and animal care. And the scientific lessons the Zoo stands to learn going forward from its first lion cubs in 20 years are not insignificant.
The Zoo's adult lions meet in their enclosure for the first time. (Meghan Murphy/NZP)
Building a Pride
Two years before the first cub’s first breath, the vision for the Zoo’s lion pride was already taking shape. In 2008, keepers Rebecca Stites and Kristen Clark began to consult more than a dozen other institutions to learn about how they built their prides. This initial legwork helped Stites and Clark draft protocols, goals, and timelines that they could use to create a pride starting with the National Zoo’s three lions: sisters Naba and Shera and our male, Luke.
The three had come to the Zoo in 2006 from a private reserve in South Africa with a specific recommendation to breed from the Association of Zoos and Aquariums’ Species Survival Plan (SSP) for African lions. An SSP matches individual animals across the country for breeding in order to maintain a genetically diverse and sustainable captive population. Because the trio’s genes were not represented elsewhere in North America, they were among the most genetically valuable lions in the country. Any offspring they produced would play an important role in a sustainable captive population.
But just because the SSP makes a recommendation doesn’t mean that the animals are going to abide by it. For a full year after Stites and Clark drew up their original protocols, the animal-care team slowly introduced Luke to Shera and Naba, giving them access to one another through a mesh opening, called a “howdy door.” By allowing the lions to become familiar with one another’s smell, looks, and temperament, animal-care staff aimed for a peaceful meeting when the time was right to put the three together.
In December 2009, keepers began to put Naba and Shera in separately with Luke for short periods of time indoors, carefully observing their interactions. The most intense introduction came in March, when all three lions met in the yard for the first time. They scuffled fiercely, or so it would appear to an untrained eye. But for Clark, who was assigned to call it off if things got too violent, the experience was successful—if nerve-racking.
“Even with Luke getting beat up for about two seconds in the yard, that’s part of the process, and we have to let the animals work it out,” says Craig Saffoe, interim curator for lions and tigers. “That’s probably very scary for people to watch. We were nervous because those encounters can quickly turn, and an animal can be hurt or killed. Without seeing that kind of aggression and how Luke responded, we never would have been comfortable with whether Luke could hold his own.”
The Zoo’s progress in building a lion pride doesn’t look so different from how it happens in the wild. The nucleus of a pride is a family of females, while different males come and go as the “resident male.” One or two young males from outside of the pride will challenge the resident male, usually an older lion, for that spot. These battles are often bloody and to the death, Saffoe says. But that’s just the first step. After the resident male has been overthrown, the females have to decide if they’ll accept the new male or males.
If he’s approved, the new resident male will assume dominance, breeding with the females that are in heat or killing the pride’s cubs so that the females will start to cycle again (they won’t do so while nursing). So essentially Naba and Shera were trying to decide whether Luke was worthy of being their resident male. Eventually, he proved his worth and was breeding with both females.
Lioness (Mehgan Murphy/NZP)
The Science of Success
Once a pride is established, lions are relatively easy to breed compared to other great cats, most of which are solitary. That’s why scientists were baffled when few cubs were born in the U.S. between 1999 and 2005. Those that were born, moreover, had a low survival rate.
This dearth of cubs came after a five-year breeding moratorium around the country, when the SSP suspected that African and Asian lion species had been allowed to breed with one another. That’s when the National Zoo stepped in. In 2005, Budhan Pukazhenthi, a reproduction physiologist at the Smithsonian Conservation Biology Institute (SCBI) and reproductive advisor for the lion SSP, began to study captive lion reproduction to figure out why lions were having trouble reproducing. Pukazhenthi and a team of scientists monitored the reproductive cycles of 20 lions in zoos across the country and ultimately found that the drought may not have had anything to do with the animals at all.
“We believe the decline might be attributed to lack of experience amongst animal care managers,” Pukazhenthi says. “When you stop breeding animals for a long period of time, you lose people from institutions with knowledge. When new people come in, there’s a learning curve.”
Although lions don’t appear to have any trouble breeding now, lessons learned from the reproductive study that Pukazhenthi spearheaded helped the Zoo determine whether Shera and Naba were pregnant this year. The study confirmed that the length of pregnancy for a lion is 105-110 days and helped Zoo researchers become the first to determine that the length of a pseudopregnancy, or false pregnancy, is about 55 days.
This was vital information. Cats can show all of the signs of being pregnant, including gaining weight, without actually being pregnant. Under these conditions, determining whether they are indeed pregnant is nearly impossible through behavioral and physical changes alone.
The answer to whether Shera and Naba were pregnant lay in hormones found in their waste. To analyze those hormones, Sarah Putman, a technician in the endocrinology lab at SCBI, had to collect their poop, freeze it, dry it, crush it, sift it, weigh it, add alcohol to it, boil it, and then dilute it. The whole process takes about two weeks.
Putman was looking at progesterone levels. If a female lion ovulates spontaneously after copulation but doesn’t get pregnant, the progesterone levels will be high for 50 to 55 days (halfway through a 110-day pregnancy) and then drop back to baseline levels. If she’s pregnant, however, the progesterone levels will stay high for the remainder of her pregnancy.
Expectation turned to joy on May 18, when Naba gave birth to a single cub. Joy soon yielded to sorrow, however, when the young male inhaled a straw seed. It punctured his lung, giving the cub pneumonia. He died on May 21. It was a hard reminder that 30 percent of captive lion cubs don’t survive their first year (compared to a 70 percent mortality rate in the wild).
Lion cubs (Mehgan Murphy/NZP)
By summer, Naba was pregnant again, and Shera was expecting as well. On August 31, Shera gave birth to a litter of four. Naba's litter of three came along three weeks later, on September 22. With those births, the pride had ten members.
A pride of lions provides the Zoo with an unparalleled opportunity to study lion reproduction, behavior, and health. Armed with this knowledge, the Zoo is positioned to help other institutions breed their animals and build prides of their own. In the months to come, the Zoo will also have some challenges to grapple with.
For example, having ten lions puts the Zoo at about capacity for the number of these animals it can manage at one time. But when Shera and Naba begin cycling again, they could potentially breed anew with Luke. Right now, the primary option for preventing this will be to pull Luke and eventually the male cubs out of the mix to form their own “bachelor pride.” What researchers don’t know—and aim to find out—is how safe it is to use some form of contraception on the female lions and whether doing so will affect their ability to successfully breed when use of the contraception is stopped.
In April, the African lion SSP will meet to determine which institutions need lions and which have lions to send out. Given their genetic value, the Zoo’s cubs will no doubt be a part of that conversation as the SSP determines where they will be sent— and when. Before the SSP matches lions with mates, the animals are put through rigorous background checks. They must be healthy, sexually mature, and capable of breeding. Saffoe predicts that the cubs will stay at the National Zoo until they are at least one or two years old.
Before going on exhbit, each cub had to demonstrate its ability to swim in the moat surrounding the lion enclosure. (Mehgan Murphy/NZP)
In the meantime, visitors to the Zoo and the Zoo’s website will continue to watch as the cubs grow and encounter new situations. “The response is pretty overwhelming from the public,” Clark says. “It’s like we’re all in this together. They’re seeing what we’re seeing, and we’re not hiding anything from them. They get to experience the same milestones and challenges that we do. By witnessing this unfold, I hope the public gains an appreciation for how much work goes into building a pride and understands how essential these animals are.”
— LINDSAY RENICK MAYER is a public affairs specialist for the Smithsonian's National Zoo.
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