A series of computer models revealed what could happen to a lion population 50 years from now if lions are shot at age three and four compared with five- and six-year-olds.
The researchers discovered that shooting lions six years old or olderregardless of numberhad almost no impact on the population over a 50-year period. But just removing a couple of three- or four-year-old lions could cause extinctions or population crashes.
"Most hunting has been based on [conservation] quotas, with little regard to the age of the animals killed," Packer said. "But all our results prove how important age is to the health of the future population."
To date, trophy-hunting programs have relied on harvesting a set number of lions a year, or a quota. Quotas are easy to administer and regulate but are based on population estimates that are often wrong. Leopards, lions, and cheetahs, for example, are elusive, and estimates of populations made by government biologists vary widely.
Packer's scheme abolishes the traditional quota system and instead permits unrestricted hunting of male lions provided they are more than six years old. He will discuss this new approach with park directors in Botswana and Tanzania within the next few weeks.
Rather than enforcing quotas, park managers and game reserves need to enforce a minimum age for trophy lions, Packer said. The reason is mired in the lions' complex life history.
Male lions reach sexual maturity at about the age of 30 months, when they are usually forced out of their birth pride to lead a nomadic existence. At age three or four, a coalition of a few young males typically challenges pride males and initiates a takeover.
If they are successful, they kill the cubs sired by the previous coalition and proceed to mate with the females. In general, males only rule a pride for two or three yearslong enough to rear a single batch of cubs to independencebefore they are ousted by more vigorous, younger, males. By age six, many males have been kicked out of a pride.
Although lions six and older are not neccesarily "surplus," many of them will have made a genetic contribution by then. But more critically, "if a male lion dies after reaching six, there should be little impact on the population," said Luke Hunter, a conservation biologist and coordinator of the Global Carnivore Program at the Wildlife Conservation Society in New York. "It shows that whether these animals are removed by car, a hunter, or another animal, it is not going to make a difference to the ability of females to leave a generation of cubs."
Not everyone agrees with this approach.
"This is not the law of the jungle," said Steve Njumbi, a program officer in Kenya for the Massachusetts-based International Fund for Animal Welfare. "By targeting the black-nosed lions, we are choosing the oldest and the strongest lions. It is not for humans to decide when these animals should be removed from the population, or that an animal has completed its reproductive contributions. A lion is only defeated when another lion displaces himthat is the law of natural selection."
Killing young lions age three and older initiates rapid turnover of pride males, causing the lion population to dive; males are removed before they have had an opportunity to mate or before they can rear their cubs to independence.
By killing too many lions, hunters can drive the lion population to extinction. Basically there are no lions left to impregnate the females, leading to a "convent situation," Packer said.
"This is an incredibly important paper. We are losing lions outside the parks all over Africa because they are regarded as a pest and nuisance," said Laurence Frank, a research associate at University of California, Berkeley, who has been studying lions in the Laikipia district in Kenya for six years. "Unless these animals are making tourist dollars they are just a nuisance to people. The only way for these animals to earn a living [for Africans] is through trophy hunting."
In Kenya, where hunting has been prohibited for 25 years, 70 percent of the wildlife has been lost, and the lion population has dropped catastrophically, Frank said.
Lions are poisoned and shot by pastoralists in retaliation for eating cattle and other livestock. Other animals are killed and sold for a few shillings as meat.
"A zebra fetches about [U.S.] $30 as meat, versus $500 as a trophy. A big lion could easily fetch $30,000 or moresome of which could compensate the community for the cattle eaten. I'm not in favor of trophy hunting, per se, but it gives the wildlife value that it doesn't have now," Frank said. His study of lion conservation and lion-human conflict is funded in part by National Geographic's Committee for Research and Exploration.
Njumbi believes that hunting is a disruptive and intrusive activity. "You can't shoot animals and expect it not to disturb lion society and the ecology of the area. If people want to hunt they should say sothey should not hide behind excuses and say there are ecological arguments or that it will benefit the community."
Hunting a "Necessary Tool"
"I personally don't like shooting of big cats, but given that it does happen, there is good that can come of it," Hunter said.
Hunters control an enormous amount of African wilderness and can contribute to conservation. A good model, Hunter said, is water bird hunting in the United States, where hunters have bought large chunks of wetlandwhich preserves land for the birds and provides land for recreational hunting.
"This is a novel and interesting study that is of great practical significance, because it actually suggests a practical way to suggest which trophies should be shot to achieve a sustainable harvest," said Nigel Leader-Williams, the professor of biodiversity management at the University of Kent in the U.K. "The system would still require a good enforcement strategy to ensure that only old lions with mostly black noses were being killed," he said.
The black-nose strategy still needs to be tested in the field. It remains to be seen whether an excited hunter would take the time to examine a lion's nose before pulling the trigger.
Packer's report has broader implications for trophy hunting. If age-related characteristics could be identified for several species, these physical cues would target only males of a "threshold age" that had completed their genetic contribution but also possessed the highly sought trophy characteristics, such as large manes, antlers, horns, or tusks.
"I view hunting as a necessary tool in conservation. And a new approach is necessary to guarantee a long-term sustainable off-take of lions. If we look ahead both conservationists and hunters both have the same long term interest," Packer said.
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