A key to saving elephants may be their own dung. Researchers have demonstrated a new way of identifying where the pachyderms are being slaughtered by analyzing DNA from confiscated ivory and matching it to excrement sampled from nature reserves. The technique could provide clues to the mysterious smuggling routes used by international criminal networks.

Tracing the origin of seized ivory is “a really critical piece of the puzzle,” says conservation biologist George Wittemyer of Colorado State University, Fort Collins, who was not involved in the study.

African elephants are in crisis, facing an onslaught of poaching for the valuable ivory in their tusks. More than 50,000 were likely killed in 2013, according to conservation biologist Samuel Wasser of the University of Washington, Seattle. This number is a significant toll on the continent-wide population of about 434,000 elephants. Last year, a study suggested that 75% of elephant populations in Africa are shrinking due to poaching.

DNA is a useful tool in fighting the trade in illegal wildlife. It has been used to confirm the identity of many kinds of contraband from rare and endangered species, such as fins harvested from protected great white sharks. In 2003, Wasser figured out how to extract DNA from ivory. The hope was to help identify where elephants were being killed. Working with Interpol, the International Criminal Police Organization, Wasser and colleagues have now sampled DNA from 28 large seizures of African ivory—each more than a half-ton—that police and custom officers had confiscated in Africa and Asia between 1996 and 2014. Large shipments like these make up 70% of ivory that is seized. “We are talking about the majority of ivory being moved around the world,” Wasser said at a press teleconference. “It is really staggering, the extent.”

To figure out where the ivory came from, the team matched its DNA to a database of DNA samples from African elephants, which took about 15 years to create. Wasser and his colleagues had gathered samples from the field, in some cases relying on trained dogs to locate dung. Other researchers contributed samples, too. All told, they had DNA from 1001 savanna elephants and 349 forest elephants from 29 countries. “It’s really a herculean effort,” Wittemyer says. By analyzing small stretches of DNA, called microsatellites, Wasser’s team found representative patterns for individual nature reserves on the scale of a few hundred kilometers, they report online today in Science.

The ivory showed a major change in poaching patterns. Before 2006, Zambia and the Democratic Republic of the Congo (DRC) were hot spots. Then the poachers apparently shifted their targets, because the elephants disappeared from eastern DRC and international attention had ramped up pressure on Zambia (because it wanted to sell stockpiles of ivory), said Bill Clark, an adviser to Interpol and a co-author of the new paper, in a press teleconference. Almost all of the 22 shipments of ivory seized after 2006 had been poached in two other places: savanna in southeast Tanzania and northern Mozambique, and forests that span parts of Gabon, Republic of the Congo and the Central African Republic. Other lines of evidence, such as surveys of carcasses and isotopic analysis of poached tusks, also suggest these areas are rife with poaching. What is notable about the new study, says geneticist Rus Hoelzel of Durham University in the United Kingdom (who was not involved in the study), is the scope of the analysis and the potential for rapidly identifying the source.

The DNA analysis is a useful tool for law enforcement, Clark said, as it can help clarify smuggling routes. It shows, for example, that most of ivory was shipped via other countries, not where it was poached. “There are false trails put down intentionally,” he said. Wasser said the key action should be increasing political pressure on countries by tying international aid to progress on fighting poaching and smuggling.