Africa’s forest elephants have nowhere to hide. Even those living in isolated wilderness in Gabon, in Central Africa, are vulnerable to poachers, scientists report today. Their analysis reveals that more than 25,000 of Gabon’s forest elephants—some 80%—were killed between 2004 and 2014. That’s another grim bit of news for the forest elephants (Loxodonta cyclotis): A similar study in 2013 found that their numbers across Central Africa dropped 62% since 2002.

Conservationists had thought that the elephants would thrive in large, intact landscapes, even without active guarding or armed patrols. But the new data show that wilderness itself offers little protection.

“The loss of elephants at this site is even graver than we thought,” says Fiona Maisels, a conservation scientist with the Wildlife Conservation Society in New York City who was part of the 2013 study. She was not involved with the new work, which she says is based on a “more intense” survey inside one large reserve and its buffer lands. “This is one of their last strongholds,” adds George Wittemyer, an elephant conservationist at Colorado State University in Fort Collins, who was not involved in the study. “Their last bastions are now being eroded.”

This bastion includes the 7570 square kilometers of Minkébé National Park, established in 2002 to protect the elephants, and 2403 square kilometers of the adjoining buffer zones. Isolated from cities and villages by dense forest and swamp, the park lies 48 kilometers from the nearest major road in Gabon. “It had the highest density of elephants in Central Africa and was very hard to get to,” says John Poulsen, a tropical ecologist at Duke University in Chapel Hill, North Carolina, and a co-author of the new study.

To estimate the elephant population, scientists counted the number of dung piles they encountered along 43 transect paths, each 1 kilometer in length, in 2004. A decade later, they repeated the exercise, adding 66 transects for a total of 106. These data suggest that from 2004 to 2014, the number of elephants in and around the park plunged from about 35,000 to about 7000, they report today in Current Biology. “We knew we’d see a decline,” says Poulsen, “but we hadn’t expected one that drastic.”

Gabon’s government had not realized the scale of the poaching: It had created an agency for national park police only in 2012. Between 2012 and 2015, guards at the park recorded just 161 poached elephant carcasses, which are difficult to find in dense forest.

To figure out what caused the massive decline, the scientists analyzed the distribution of the dung. They found fewer piles in the southern area, close to logging roads. Elephants there were most likely targeted by poachers in Gabon, Poulsen says. The park’s northern and central regions had almost no dung, leading the scientists to suspect that poachers from Cameroon wiped out these elephants. They base their hunch on three factors: The nearest Cameroonian road is just 6.1 kilometers from the park; Cameroon’s known role in the illegal ivory trade; and an unauthorized gold mining camp in the center of the park. In 2011, Gabon’s National Parks Agency expelled more than 6000 illegal immigrants—most of them Cameroonians—from the camp. “It shows that poachers will do anything and go anywhere to kill elephants as long as there’s a market for ivory,” Poulsen says.

To save the animals, cross-border law enforcement measures and patrols are urgently needed, the scientists say. They have also called on the Convention on International Trade in Endangered Species of Wild Fauna and Flora to recognize forest elephants as critically endangered and in need of the highest protection. But ultimately, the solution lies in reducing or eliminating the global demand for ivory—as China recently promised. “As long as some countries persist in their ‘right’ to trade in ivory, there will be cross-border poaching,” says Phyllis C. Lee, an animal behaviorist at the University of Stirling in the United Kingdom, who was not involved in the study. “That’s clear for all to see now.”