The lions in southern Africa's Kgalagadi Transfrontier Park are among the toughest and strongest on the continent. But they're not as tough as this hero in a half shell.

The tortoise's tough exterior proved too strong for the canines and claws of this pair of young lions.

The two youngsters were first spotted by Kgalagadi regular Peet van Schalkwyk as they were feeding on a gemsbok kill in the south of the reserve, along with the rest of their pride. After gorging themselves on the 200-kilogram antelope, the adults did what lions do best: slept off the meal.

But for two of the younger members of the pride, a passing tortoise proved to be an irresistible distraction. "The lions are approximately 18 months old, classified as large cubs," says Dr Paul Funston, Senior Lion Program Director for Panthera, the global wild cat conservation organisation.

While lions are opportunistic hunters, it's likely this encounter was more a case of curiosity than a genuine attempt at predation. "The tortoise is absolutely a curiosity for these young lions," Funston explains. "[It's] something to taunt and play with." The cats' unusual chew toy is likely an older individual with a shell strong enough to withstand some chomping. "Due to the size of the meal, tortoises can't really be regarded as lion prey," Dr Funston adds. "But there are cases of starving lions crushing open and eating smaller tortoises with less robust shells."

Big cats in this semi-desert terrain have it tough. Large antelope like gemsbok are not always easy to come by, and a lack of dense vegetation makes ambush hunting difficult. Studies have shown that the lions here often eat a variety of smaller animals like spring hares, aardvarks, bat-eared foxes and porcupines. If tortoises weren't so tricky to crack open, they may well feature on the menu, too.

And while the tortoise may disagree, the Kgalagadi Transfrontier Park needs lions. These apex predators play a vital role in the ecosystem and have a direct effect on the number of prey and smaller predators in the area. But the big cats may be heading for trouble. "Though lions are recognised and revered around the world, few people realise that Africa's lions are in crisis," Funston points out. "Just over a century ago, more than 200,000 wild lions lived in Africa. Today, only about 20,000 remain — a staggering decline."

Poaching, conflict with humans, habitat loss and hunting are the biggest threats to the iconic species. Despite the challenges though, Funston is confident that there is hope for lion populations, and much of it hinges on well-managed national parks.

The Kgalagadi Transfrontier Park is home to about 450 lions and is one of the last sizeable strongholds for the species. "Although about 30 [lions] die per year around the park in times of heightened human-lion conflict, the population is large enough to absorb these pressures and has remained remarkably stable for many years because conservation efforts allowed lion populations to recover," says Funston. "This is key for lions going forward; there is just no replacement for large national parks [and] protected areas."