Killing the eldest males will protect lion populations.
Researchers have developed a rule of thumb that they hope could save lion populations from declining at the hands of trophy-hunters. They are urging hunters to kill only males with dark noses.
A lion's nose is speckled with dark pigment, and these freckles become more pronounced as the lion ages, explains Craig Packer of the University of Minnesota in Saint Paul, who led the study.
Removing only the old males whose noses are at least 50% dappled with pigment would minimize the disruption to lion prides, his team found1. This gives cubs a better chance of survival.
Packer's team used data from 40 years of observations of lions in the Serengeti National Park and Ngorongoro Crater in Tanzania, where hunting is banned. They created a computer model that simulates the consequences of different hunting strategies.
If a young male is killed, his pride stands a good chance of being taken over by a rival, who will kill the cubs to encourage females to devote themselves to raising new ones sired by him. If a pride changes hands too often, fewer cubs make it to adulthood and lion numbers slump.
The team calculate that populations will not decline as long as hunters target only males over five years old. These lions are old enough to have already raised their cubs to adulthood. In the populations Packer studied, five-year-old males had noses half-blackened with pigment.
This rule shouldn't upset hunters, Packer argues. "Hunters get the older males, which are the best trophies anyway," he says. "They're spectacular-looking."
Current rules on lion hunting vary from country to country, but they generally set a quota for the number of animals that can be killed. These can be males of any age.
But quotas are controversial, as there is often some dispute about how many animals are in the field and how many can be shot while keeping the population sustainable.
The new rule of thumb could negate the need for quotas, Packer suggests. And, because it is so simple, it could prove more useful for conservation. "Hunters need to have clues they can spot in the field - if you have more complex rules, hunters will ignore them," says Claudio Sillero, head of conservation with the Born Free Foundation, a British campaign group.
Some hunters are respectable but some are complete cowboys Andy Loveridge , University of Oxford
But Andy Loveridge, a conservationist at the University of Oxford, UK, who studies sustainable hunting in Zimbabwe, says the rule needs to be rigorously policed in order for it to work. "It presupposes that hunters behave in an ethical way," he says. "Some are respectable but some are complete cowboys."
Lion hunting is a rich man's sport. Most agencies that offer lion hunts charge more than US$3,000 just for a licence to pull the trigger. Factor in the cost of guides, park-management fees and taxidermy charges, and a two-week safari can cost up to $30,000.
The lucrative nature of hunting could prompt those who support lion hunting to aid conservation, says Packer. After all, if lions go extinct, they go out of business. "In the long term, there's really no conflict between trophy-hunters and conservationists," he says.
Whitman, K., Starfield, A. M., Quadling, H. S. & Packer, C. Sustainable trophy hunting of African lions. Nature, published online, doi:10.1038/nature02395 (2004).
University of Oxford
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Hopkin, M. Hunters urged to shoot only dark-nosed lions. Nature (2004). https://doi.org/10.1038/news040216-22