New Forensic Technique may Track Illegal Ivory


New Forensic Technique may Track Illegal Ivory

July 01, 2013

Epic Elephant Slaughter Leads Scientists to Develop Dating Tool

Nearly 25 years after an international ban was placed on ivory, African elephants are being slaughtered at a rate that could bring about their extinction this century. By allowing the trade of ivory acquired before 1989 to continue, the ban put the burden on law enforcement to distinguish between legal ivory and poached. Now, a new method for dating elephant tusks, described in the latest issue of the Proceedings of the National Academy of Sciences (PNAS), could make it easier to enforce the ivory ban and save the African elephant from extermination say researchers. The method might also be applied to endangered rhinoceroses and other wildlife.

“We’ve developed a tool that allows us to determine the age of a tusk or piece of ivory, and this tells us whether it was acquired legally,” said the study’s lead author, Kevin Uno, a postdoctoral researcher at Columbia University’s Lamont-Doherty Earth Observatory. “Our dating method is affordable for government and law enforcement agencies and can help tackle the poaching and illegal trade crises.” 

Elephant tusks grow ring by ring, recording what plants the animals ate. Elephant tusks, it turns out, also record how much radioactive carbon was in the air, giving scientists a time marker for all those meals. During photosynthesis plants absorb radiocarbon put into the air by nuclear weapons testing in the 1950s and 1960s. The radiocarbon travels up the food chain, finding its way into the fingernails, hair, teeth and tusks of animals. By comparing radiocarbon levels in those tissues against the fluctuating “bomb curve” of radiocarbon in the atmosphere, forensic scientists can pinpoint when the tissues formed, and in some cases, when the animal died. The method works for tissue formed from about 1955 until the bomb curve, or concentration of carbon 14 isotopes in the air, reaches background levels, 10 to 15 years from now.

In the highly-regulated market for legal ivory, finding tusks for scientific research is not easy. With the help of a Salt Lake City zoo and several agencies in Kenya, the researchers gained access to the tusks of two elephants: Misha, euthanized at Utah’s Hogle Zoo in 2008, and Amina, who died naturally at Kenya’s Samburu National Preserve in 2006. Study co-author Thure Cerling, a geochemist at the University of Utah, read about Misha’s death in the local newspaper and immediately called the zoo. “They told us, we can work with you because we haven’t buried her yet,” he said. The researchers traveled to Kenya for Amina’s tusk, which they sawed into domino-sized samples under the watch of Kenya Wildlife Service.  

In the lab, the researchers measured radiocarbon levels at the base of each tusk to independently calculate when the elephants died. Similar tests were done on monkey hair, hippo canines, oryx horn and elephant tail hairs to verify that the method worked across tissues of different ages. Two steps were key to getting precise ages. The researchers sampled each tusk lengthwise, along the growth ring, and used the most advanced technology--an accelerator mass spectrometer--to measure the radiocarbon. In addition, the study calculated growth rates for the teeth, which can be applied to elephant teeth in the fossil record to understand how climate and vegetation varied in Africa when humans were evolving. In other applications in wildlife forensics, the technique can be applied to rhino horns, which are intensely sought after for their perceived medicinal benefits.

The researchers’ method complements a forensics tool developed at the University of Washington’s Center for Conservation Biology that allows researchers to track ivory seizures back to their source. In a 2004 study in PNAS, center director Sam Wasser laid out a map of African elephant populations based on DNA from their dung that, when matched against a piece of seized ivory, could tell investigators where the ivory originated. The DNA tool has helped law enforcement identify where elephants are being poached; the new radiocarbon tool tells them when. “It can reliably tell us, is it legal ivory or not?” said Wasser, who was not involved in the study.

Elephant poaching is now at its highest level since record-keeping began in 2002, according to a 2012 report by the Convention on International Trade in Endangered Species (CITES). More elephants are slaughtered today—at the rate of 30,000 a year--than before the 1989 ban, experts say. Some 423,000 African elephants are left, according to the International Union for Conservation of Nature’s elephant database

Much of the illegal ivory leaves Africa through Tanzania and Kenya and ends up in Asia, where it is carved into religious icons, decorative art and signature seals popular among the Chinese and Japanese. While China imports about 70 percent of the smuggled ivory, the next biggest market is the United States, where ivory is worked into the handles of guns and knives, said Richard Ruggiero, an expert at the U.S. Fish and Wildlife Service. Global seizures of illegal ivory reached a new record in 2011, at 86,000 pounds (39,000 kilograms), equaling nearly 6,000 elephants. But the magnitude of the problem is no match for law enforcement.  “With poaching rising exponentially because of exploding demand we are actually losing ground,” said Ruggiero.

A kilogram of ivory—about 2.2 pounds--fetched $200 in 2004; by 2007, a kilo was worth $850. Escalating prices are driving Africa’s notorious militias, including the Lord’s Resistance Army in northern Uganda and south Sudan, the Shabab in Somalia and the Janjaweed of Darfur to kill elephants for tusks to buy guns, The New York Times reported last year. Organized crime is now involved in smuggling ivory out of Africa, leading former U.S. Secretary of State Hillary Clinton to speak out against the problem last year. At a Senate Committee of Foreign Relations hearing last year, former U.S. Sen. John Kerry (now Clinton’s successor) testified to the global security threat posed by elephant poaching.

The disappearance of the African elephant will mean more than the loss of a majestic, highly intelligent creature, ecologists say. It could change the structure of Africa’s savannahs and rain forests. “They are environmental architects,” said Wasser. “They keep woods down in the savannah and are the most important dispersers of seeds of rain forest trees. The central African rain forest is the second most important area on earth for capturing carbon dioxide and storing it.” 

Other authors are: Jay Quade, University of Arizona; Daniel Fisher, University of Michigan; George Wittemyer, Colorado State University; Iain Douglas-Hamilton, Save the Elephants; Samuel Andanje, Patrick Omondi and Moses Litoroh, Kenya Wildlife Service.

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The study, “Bomb-curve radiocarbon measurement of recent biologic tissues and applications to wildlife forensics and stable isotope (paleo)ecology,” is available from the authors or PNAS:


Scientist contact:

Kevin Uno, 845-365-8308

More information: Kim Martineau, Science Writer, Lamont-Doherty 646-717-0134


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The Earth Institute, Columbia University mobilizes the sciences, education and public policy to achieve a sustainable earth.


Lamont-Doherty Earth Observatory seeks fundamental knowledge about the origin, evolution and future of the natural world. Its scientists study the planet from its deepest interior to the outer reaches of its atmosphere, on every continent and in every ocean, providing a rational basis for the difficult choices facing humanity.