The Lions in the Ngorongoro Crater are likely to be the descendants of just 15 cats
Tracing the history of Lions residing in the Ngorongoro Crater and what ails the 64 big cats
Ngorongoro Conservation Area, together with its adjacent Serengeti National Park, marked the 60th Anniversary of protected existence in 2019.
The conservancy is now 67 years old and counting.
The first study of its lions was conducted when Ngorongoro was only 20 years old.
In January 1979 Craig Packer with colleague and wife Anne Pusey, began their study of lions in Ngorongoro Crater, a 2,000-foot-deep caldera with a hundred square mile floor located at the eastern edge of Tanzania’s Serengeti Plain.
The crater’s cliff walls serve to isolate about 100 lions from their nearby Serengeti counterparts.
Suspecting the lions were subjected to repeated inbreeding and that they may conceal genetic vulnerabilities, the Packers set about reconstructing the family tree of at least five generations of every lion that lived in the crater.
The scientific mystery would take ten years to solve.
The method used by the Packers incorporated the monumental task of assembling and organizing all the lion photographs they could find from around the world, from biologists and scientists who had studied the crater lions, through to film crews and tourists who had journeyed to the crater floor since the road granting access was completed in 1959.
The Lion and the Jewellery
In 1979 Packer and Pusey began using lion ID cards with pictures of individuals at various ages, noting field marks such as whisker spots and ear notches to pinpoint lions.
They contacted preceding researchers who had photographed or drawn the same lions or their forebears and solicited photographs taken by tourists, receiving hundreds to help fill in the gaps.
Eventually their catalog put faces on more than 500 individuals, most now dead.
Their detective work determined that all of today’s crater lions descend from only 15 lions that either survived the flies or invaded Ngorongoro shortly thereafter.
The studied chronology revealed that the entire crater population descended from 15 animals.
Only eight individuals survived the plague while the others were males that may have entered the crater from the adjacent Serengeti plains.
The plague had removed so many adult males from the crater that fresh blood was able to enter.
Once the residents resumed breeding, they had several large sets of sons that monopolized the crater prides and kept any additional immigrant males out.
Therefore, the current crater population has been subject to close inbreeding since 1969, about five lion generations.
The Packers invited Steve O’Brien at the National Cancer Institute and his colleagues from Washington’s National Zoo to conduct genetic studies of the crater lions in 1984.
O’Brien had surveyed the genetics of several different cat species through his research on feline leukemia.
Genetics and reproductive physiology of the crater lions were assessed by comparing them with the nearby Serengeti lions, since long-term studies of the Serengeti population had shown that close inbreeding is almost nonexistent in that area.
Fast-forward to 35 years ago, in April 1992 to be precise, Craig Packer published his recollection of Ngorongoro Lions after a study he conducted with his wife 13 years earlier.
Killed for Hunters’ ego
This is the account from Craig’s Lions of Ngorongoro Crater, Published in 1992
“I visited Henry Fosbrooke again in October 1990. When I told him that I suspected the crater lions had been through previous periods of genetic decline,” writes Packer.
Fosbrooke, who is the first conservator of Ngorongoro, then retired and living at the shores of Lake Duluti in Arusha, led Craig into his large library and told him, ‘You should read these.’
They were accounts of big-game expeditions that went into the crater in the early twenties.
During two weeks in 1922 one hunting party bagged seven adult lions and badly wounded another three.
The last expedition was in 1924, when five more lions were killed.
Considering that there are never more than about 30 adult lions in the crater and that most of the wounded animals probably died as well, the breeding population must have been severely reduced.
“Our genetic assays more than 60 years later may well have revealed the results of this onslaught!”
The Serengeti and Ngorongoro were declared wildlife sanctuaries in the late 1920s to protect the lions from further hunting.
Ngorongoro Crater became a world heritage in 1979 in recognition of its special significance as a microcosm of African savanna.
The popular appeal of charismatic carnivores such as lions has often led to the conservation of habitat that sustains a host of other species.
But living at the top of the food chain inevitably means that predators often end up in small, threatened populations.
The history of the crater lions may represent the future for many other large vertebrates.
The Inbreeding factor
Increased human habitation around Africa’s national parks has formed virtually impermeable boundaries, and recently many species have become isolated in small populations, making them even more vulnerable to environmental catastrophe.
Add to this the effects of close inbreeding, and many small populations may well be caught in a downward spiral.
Ironically, according to Packer, they are strong enough to deter what their population most needs — the entry of outside lions with new genes ‘Perpetuating these populations will require more than just protecting them from hunters and poachers.
The crater lions are conspicuous and have therefore proved surprisingly easy to monitor. The fates of most other small populations will run their course undetected.’
There were two reasons to suspect the crater lions were inbred:
No new lions had entered the crater during the previous four years
A report suggesting the population of crater lions had been devastated by a plague of biting flies in 1962
According to Henry Fosbrooke, the first conservator of the Ngorongoro Conservation Area during 1961 and 1962, exceptionally heavy rains permitted the biting fly Stomoxys calcitrans to breed constantly for more than six months.
By May 1962 the crater had switched from heaven to hell for the lions.
Most lions became emaciated and covered with festering sores, and while many sought shelter by climbing trees or hiding in hyena burrows, they eventually became so ill they were no longer able to hunt.
By the time the rains finally abated, Fosbrooke estimated the population of at least 70 lions had been reduced to about ten.
The crater seems to be the main feature of the Ngorongoro Conservation Area.
It was formed when a large volcano erupted and collapsed on itself two to three million years ago, is 610 metres (2,000 feet) deep and its floor covers 260 square kilometres (100 square miles)
The Bygotts studies
By 1972 the Lion population in the crater was reported to have recovered to its former levels and was distributed among three prides and by 1975, the Bygotts reported lions on the crater floor dispersed among five prides.
Jeannette Hanby met David Bygott as zoologists studying primate behaviour at the University of Cambridge, England.
After their marriage the Bygotts then went to Serengeti National Park to continue the long-term Lion Project.
As part of their work on comparing lions in different habitats they extended the study into Ngorongoro Crater.
The Bygotts documented that, compared with singletons and pairs, male lions in groups of three or more can more reliably gain tenure of female prides, retain tenure for longer, mate with more different females, and produce more surviving offspring; thus, each individual has higher fitness through cooperation.