In November, 2011, a caravan of poachers—as many as a hundred, by some counts—crossed into the Central African Republic on horseback from Sudan. They rode seven hundred miles along the northern border, and entered Bouba-Njida National Park, in Cameroon. The caravan included a pack train of camels loaded with AK-47s, bags of ammunition, heavy machine guns, and two mortars. The poachers had been in the park before, in 2010, when they killed about a dozen elephants and two park guards. This time, they were shooting elephants in far greater numbers, and in some cases sawing off the tusks while the animals were still alive. Céline Sissler-Bienvenu, a regional director for the U.S.-based International Fund for Animal Welfare, heard about the slaughter, travelled to the park, and notified the authorities in Yaoundé, the capital. Cameroon’s government sent a contingent of Army troops to drive the poachers out. A handful of people on each side were killed or wounded in skirmishes, but the poachers, who were by then better acquainted with the park’s geography, continued about their business.

“They were very well organized,” Sissler-Bienvenu recalled. “Very well armed, very strategic, and they implemented ambushes in military style.” Some of the men were believed to be members of Rizeigat, a nomadic Arab group with ties to the janjaweed and to the Darfuri genocide. They cut pieces from the elephants’ ears to use as gris-gris. The manager of a lodge in Bouba-Njida Park, who encountered a group of the poachers on horseback, recalled, “When you looked at them, they stared straight back at you. They didn’t fear anything from anybody.”

As the killings continued, Sissler-Bienvenu went to the press, and soon Le Monde ran a story featuring photographs of elephants with their trunks missing and their faces cut off. A copy of the newspaper found its way to Cameroon’s President, Paul Biya, who was staying at a hotel overlooking Lake Geneva. He ordered an additional three hundred troops into Bouba-Njida, but they, too, failed to drive out the poachers. In the three months that the poachers were in the park, they killed six hundred and fifty elephants.

After leaving Cameroon, the men split into smaller groups, and four of them apparently detoured north, toward Zakouma National Park, in neighboring Chad, where, just outside the park, they slaughtered nine more elephants before rangers spotted their camp from the air. When the rangers reached the camp, three of the poachers were out hunting; the fourth escaped on foot, and his horse was killed in the crossfire. The rangers found thousands of rounds of ammunition, along with uniforms, documents, and phones linking the men to specific Army and paramilitary units in Sudan. The poachers remained at large. Three weeks later, at dawn, as a group of Muslim park guards knelt in prayer, the poachers shot them all in the back. They seized the guards’ horses and fled to Sudan.

The Bouba-Njida attack was one of the bloodiest massacres of elephants to date, and represented a serious escalation in the tactics and the daring of poachers in Africa. George Wittemyer, the chairman of the scientific board of the conservation group Save the Elephants, characterized the event as a “significant awakening,” involving “a terrorist militia coming into a relatively effectively governed country and engaging successfully with the Army—even, arguably, driving it off.”

Elephants are under siege throughout Africa. Demand for ivory is increasing in Asia: once prized by Chinese aristocrats, it is now sought by members of China’s growing middle class, who buy ivory cigarette holders, chopsticks, and even carved miniature elephants. In Hong Kong, a hub of illegal trade, ivory can sell for three thousand dollars a pound. The price has tripled in the past four years, and a pair of carved tusks can be worth two hundred thousand dollars. The poachers themselves are paid much less—only a hundred or two hundred dollars a pound—but that goes far in Africa. Criminal organizations trafficking in illegally obtained ivory have sprung up in recent years, and the money involved has begun to attract terror groups—not just the janjaweed from Sudan but also, according to reports, the Shabab, from Somalia, and the Lord’s Resistance Army, from the Democratic Republic of the Congo and the Central African Republic. The overlap of organized crime and terrorism has become a concern for the Obama Administration, which recently announced an aggressive plan to involve American intelligence agencies, including the F.B.I. and the D.E.A., in tracking and targeting wildlife traffickers.

The forest elephants roaming the dense jungles of the Congo Basin, south and east of Cameroon, have only recently been identified as a species distinct from the larger, savanna elephants found at Bouba-Njida and elsewhere on the continent. Because their habitat is virtually inaccessible, little is known about them. Stephen Blake, of the Max Planck Institute, who studied the feeding and range habits of forest elephants, refers to them as the “megagardeners of the forest.” The animals consume a great deal of fruit, and play a crucial role in dispersing, through their dung, the seeds of tropical fruit trees. Blake described to me their “extreme spatiotemporal intelligence,” and their ability to keep track of one another in the dense environment through the use of “infrasound,” a frequency below the level audible to humans. Their ivory, sometimes called hot ivory or pink ivory, is especially coveted on the illegal market.

The person who knows forest elephants best is an American researcher in the Central African Republic named Andrea Turkalo. She has spent more than twenty years camped out in Dzanga-Ndoki National Park, near a bai, or clearing, where the elephants congregate in numbers unequalled at any other site. A wryly humorous woman of sixty-three, who wears her hair in a tightly pulled-back bun, Turkalo has gained most of her expertise in the field; her only scientific credential is an undergraduate degree in environmental studies from Antioch College, in Ohio. She spends much of her time alone or in the company of local trackers. When I visited her camp, a few months ago, she told me that she grew up in Taunton, Massachusetts, in a working-class family. Her father, a Second World War veteran, was a guard at the Bridgewater state prison; her mother taught in a school for children with special needs. The Taunton Public Library sustained Andrea from the age of six, and she still checks books out from there electronically and reads two a week on a Nexus tablet. She said that she’d just finished Edvard Radzinsky’s biography of Stalin and Caroline Moorehead’s “A Train in Winter,” a history of French Resistance women imprisoned at Birkenau. “That’s why I like being here,” she said. “You have time to focus on things.”

Turkalo arrived at Dzanga-Ndoki in 1990, after working in the Peace Corps elsewhere in the Central African Republic. She and her husband at the time, the explorer Mike Fay, had been hired to run the new park. “I liked elephants, but I never thought I’d end up studying them,” she told me. But then the couple discovered the clearing, called Dzanga bai, several miles away. “The first time we went out there, we pitched a tent right on the bai,” Turkalo said. “We heard the elephants calling the entire night.”