The Grauer’s gorilla, the world’s largest primate, has been a source of continual worry for conservationists for more than two decades. Longstanding conflict in the deep jungles of the eastern Democratic Republic of Congo left experts with no choice but to guess at how that gorilla subspecies may be faring.

Now, with tensions abating somewhat, researchers finally have an updated gorilla head count — one that confirms their fears. According to findings compiled by an international team of conservationists, Grauer’s gorilla populations have plummeted 77 percent over the last 20 years, with fewer than 3,800 of the animals remaining.

“We suspected that the Grauer’s gorilla had declined because of all the insecurity in the region, but no one had an idea of how much they’d declined by,” said Andrew Plumptre, director of the Wildlife Conservation Society’s Albertine Rift Program in Central and Eastern Africa. “It turns out that the rate of collapse pushes this subspecies to the verge of extinction.”

Grauer’s gorillas — named after Rudolf Grauer, an Austrian explorer and zoologist who first recognized the apes as a separate subspecies — resemble their close relative, the mountain gorilla, save for their longer limbs and shorter hair. Although Grauer’s and mountain gorilla populations were once connected, years of isolation have left them genetically distinct enough to warrant separate designations as eastern gorilla subspecies.