The species already has a strong track record in detection. The Belgian organization APOPO has been training its “heroRATS” to find land mines for 20 years, and it says the animals have helped clear more than 100,000 mines from former war zones. In the past decade, the rats have been used to detect tuberculosis, a highly infectious disease that public-health facilities often miss. They can screen 100 mucus samples in 20 minutes — a job that would take clinics four days — and APOPO says the rats have boosted TB detection by 40 percent at the clinics where they are used.

Now, with funding from the U.S. Fish and Wildlife Service, the organization has begun training the keen-nosed rodents to help another animal — one at risk of going extinct. Demand for pangolins, reclusive animals that look like walking pine cones, is so great that some conservation groups say their populations in Africa and Asia have dropped 90 percent in the past decade. Smugglers often pack their dried scales with other pungent products, like coffee and wax, that can throw off detection dogs.

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The rats, which APOPO breeds at its headquarters in the city of Morogoro, are introduced to people when they’re 4 weeks old. They’re then trained for months using basic Pavlovian conditioning: The rat hears a click and gets a treat — avocado or banana — when it sniffs a target scent. Eventually, various scents are placed in holes, and the rodent gets the food reward when it stops and lingers over the target.

Using rats to ferret out pangolins could have advantages over other methods, said Cynthia Fast, APOPO’s head of training and behavioral research. X-rays are used at some ports but are expensive and can bottleneck operations. Dogs sometimes struggle in withering heat and can contract some fly-borne diseases, but not the giant rats, Fast said. And while the rats can be very affectionate, they don’t bond with individual handlers, making their training and deployment more seamless than that of detection dogs.

“They bond in general with people. If you come and visit our center, you see them following certain people around, not even on a leash. It’s the cutest thing,” Fast said. “But they do it indiscriminately.”

The trainee rats have all been named after celebrity wildlife conservationists — one is Fossey (for Dian, the gorilla researcher); another is Betty White, after the actress and animal activist.

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The pangolin project has faced some challenges. For one, it’s not easy to acquire pangolin parts to help the rats practice detection. APOPO had a lead on samples in South Africa, but securing the permits to get them across the borders — legally, that is — proved too big a hurdle, Fast said. The Tanzanian government also had some seized samples available, but they needed to be held until accused smugglers were prosecuted.

At one point, a well-meaning local man showed up at the organization’s office with a live pangolin he’d found in the wild; he’d heard about APOPO’s program and thought they might know what to do with it, Fast recalled. The group handed the animal over to Tanzanian wildlife authorities, who released it in a protected area.

Eventually, a pangolin at a zoo in Dar es Salaam, Tanzania’s former capital, died. Now its remains are being used to train the rats.

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Another complication is that pangolins are terribly pungent, with “almost a fishy smell,” Fast said. That is true both of the live animal that showed up on APOPO’s doorstep and the scales that the researchers dried in the sun, Fast said.

“It was very challenging to dry them outside and not attract a bunch of different wildlife or flies, because they are so stinky,” Fast said. It’s not easy to find other similarly potent scents for use in training, she said, though dried fish is one possibility.

“You don’t want them to miss actual samples that are being smuggled,” Fast said of the rats. “But you also don’t want to have a high number of false alarms, where the rat says, ‘Hey, there’s pangolins here . . . just to find out it’s a bunch of fresh fish.”

Fast said the pangolin-sniffing rats won’t be put to work for another two to five years, and doing so will depend on what may be the most difficult step: securing the cooperation of busy ports in Asia and Africa. The rats are also learning to detect shipments of ebony wood, which is illegally logged in Madagascar.

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Some day, Fast said, the sniffer rats might even be used to detect smuggled rhino horn, elephant tusks or lion bones.

“Here you have a rat working for fellow nonhuman animals. But it’s also still helping people as well, because of lot of who is involved in illegal smuggling and trafficking is organized crime, and they’re exploiting the local population,” Fast said. “This is one project where the rats are actually helping a lot of different levels of humanity.”