Burning and clearing of large areas of tropical forest, combined with hunting of primates for food and illegal wildlife trade, has placed many species of apes, lemurs and monkeys at risk of dying out.
These include iconic species such as the Sumatran orang-utan, Grauer's gorilla, the Northern brown howler monkey and the Hainan gibbon.
Scientists and conservation experts have now updated a report on the world's 25 most endangered primates based on the current knowledge of the animals numbers and the risks facing them.
Dr Christoph Schwitzer, a primatologist and director of conservation at Bristol Zoological Society who helped compile the list, said: 'This research highlights the extent of the danger facing many of the world's primates.
'We hope it will focus people's attention on these lesser known primate species, some of which most people will probably have never heard of, such as the Lavasoa Mountains dwarf lemur from Madagascar - a species only discovered two years ago - or the Roloway monkey from Ghana and Ivory Coast, which we believe is on the very verge of extinction.'
'Some of these animals have tiny populations remaining in the wild and support and action to help save them is vital if we are to avoid losing these wonderful animals forever.
'This report makes scary reading for primatologists and the public alike, and highlights where we as conservationists must focus our attention over the coming years.'
There are 703 species and sub-species of primates around the world.
Every two years experts from the International Union for Conservation of Nature (IUCN), the Bristol Zoological Society, International Primatological Society and Conservation International, produce a list of those most under threat.
In their latest report two species - the Philippine tarsier and the Lavasoa Mountains dwarf lemur from Madagascar - were included on the list for the first time.
The Lavasoa Mountains dwarf lemur was only discovered two years ago and its exact numbers are still unknown but its habitat is already being destroyed.
The report warned that Madagascar and Vietnam are home to large numbers of highly threatened primate species.
This is because many of the species live in isolated pockets of forest that are under threat of destruction.
The Northern sportive lemur from Madagascar is possibly the second most endangered animal to appear on the list with just 50 individuals known to survive.
The Cat Ba langur, or golden headed langur as it is also known, has just 60 individuals left on Cat Ba Island in Vietnam.
There are thought to be just 24 Hainan gibbons left on Hainan Island in China.
In Africa, the red colobus monkeys was under 'particular threat', as were some of South America's howler monkeys and spider monkeys.
The Northern brown howler monkey, for example, has less than 250 mature animals living in the wild.
The report warned: 'All of these species are relatively large and conspicuous, making them prime targets for bushmeat hunting.'
Russell Mittermeier, chair of the Species Survival Commission of the IUCN, said he hoped the report would encourage governments to commit to 'desperately needed biodiversity conservation measures'.
He said there was growing evidence that some primate species play important roles in dispersing tropical forest tree seeds, meaning they were essential to those habitats.
He added: 'The purpose of our Top 25 list is to highlight those primates most at risk, to attract the attention of the public, to stimulate national governments to do more, and especially to find the resources to implement desperately needed conservation measures.
'In particular, we want to encourage governments to commit to desperately needed biodiversity conservation measures.'
THE WORLD'S 25 MOST ENDANGERED PRIMATES
Primate species. Number remaining in the wild.
Lavasoa Mountains dwarf lemur Unknown
Lake Alaotra bamboo lemur 2,500 - 5,000
Red ruffed lemur Unknown
Northern sportive lemur Around 50
Perrier's sifaka 1,700 - 2,600
Rondo dwarf galago Unknown, but remaining habitat is just 100 square km
Roloway monkey Unknown, but thought to be on the very verge of extinction
Preuss' red colobus monkey Unknown
Tana River red colobus monkey 1,000
Grauer's gorilla 2,000 - 10,000
Philippine tarsier Unknown
Javan slow loris Unknown
Pig-tailed langur 3,300
Cat Ba langur 60
Delacour's langur 234 - 275
Tonkin snub-nosed monkey less than 250
Kashmir grey langur Unknown
Western purple-faced langur Unknown
Hainan gibbon 25
Sumatran orang-utan Unknown
Ka'apor capuchin Unknown
Northern brown howler monkey Less than 250 adults
Colombian brown spider monkey Unknown
Ecuadorian brown-headed spider monkey Unknown
Courtesy of IUCN, the Bristol Zoological Society, International Primatological Society and Conservation International
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