Bonobo apes live in Democratic Republic of the Congo (DRC) and often have sex every few minutes.
But because they have quite low fertility, are hunted for their meat and their babies are stolen as pets, their numbers are now perilously low.
The bonobos -- the closest species to humans -- are now classified as "endangered."
Evelyne Peteolot, from Lola Ya Bonobos Sanctuary near Kinshasa, said, "We know that the number of animals is diminishing in dramatic proportions."
Before the years of brutal civil war in the DRC, it was estimated there were around 100,000 bonobo apes. Now it is feared there are around 5,000, along with those housed in a handful of zoos around the world.
Peteolot said the exact number was unknown.
"It is so difficult with all the political problems here to be able to carry out a proper census," she added. "It's a species that will disappear, unfortunately, because this animal only exists [in the wild] here in Democratic Republic of the Congo. If there are no longer any left here, they will no longer be found anywhere. So they will become extinct, which is a real shame."