By Richard Black
BBC environment correspondent
One of humankind's closest relatives, the bonobo, may be facing extinction.
Bonobos share 98% of their genes with humans (Image: WWF-Canon/Martin Harvey)
Scientists working in the Democratic Republic of the Congo - the only country where bonobos live - have found evidence that they are being hunted for bushmeat in areas where they should be protected.
Numbers may be down to 20% of previous levels.
They look like a smaller, cuter version of the chimpanzee; and uniquely among animal species, they use casual sex to bond social groups.
Bonobos are as closely related to us as chimps are. But research from a coalition of conservation groups led by WWF suggests their numbers may be in sharp decline.
In areas of the Salonga National Park where previously bonobos had been abundant, scientists saw no live animals at all - they heard calls, they saw droppings and nests, but made no actual sightings.
Peter Stephenson, the co-ordinator of WWF's African Great Apes programme, said: "What was disturbing is first, that they were finding fewer bonobos than had previously been found in areas where we know bonobos to occur; and secondly, they found lots of traces of people being in the park and traces of active hunting.
"And basically as this is a national park, all of this hunting was illegal, and therefore poaching."
The root cause of the bonobo's plight is the DRC's history of conflict.
Protection work has been extremely difficult, there's been a demand for bushmeat, and armed gangs have moved into some areas of the Salonga Park.
Researchers say they encountered elephant poachers armed with semi-automatic weapons.
Militia hiding in parks are thought to be poaching bonobo (Image: WWF-Canon/Martin Harvey)
Salonga is the only area where bonobos are supposed to be protected in the only country in which they live - it is crucial to their survival.
WWF and its partners have launched a new initiative to track the remaining populations and prevent their extinction.
"It's been almost impossible for the Congolese Institute for Nature Conservation, which runs the national parks, to function properly in most of the protected areas in DRC during the war, " continued Peter Stephenson.
"Armed militias often use national parks as areas to hide out because of the dense forest; and that's been the case in Salonga too - armed militias have hidden out there - and for sure, with the easier availability of guns, it's been easier for people to hunt bonobos as well as other threatened species such as elephants.
"The problem with estimating the population of bonobos, like any other large mammals that live in dense rainforest, is it's not terribly easy to count them.
"And so over the last few decades, people's estimates of population have largely been based on counting animals in a small area, and then extrapolating up, based on the densities they find in the small areas, and trying to estimate how many there might be in the broader Congo Basin.
"So, the methods haven't up until now been incredibly accurate; but based on the efforts that have been made, we think there were between 10,000 and 50,000 bonobos in the Congo Basin."