Thirty-one leading scientists have issued an urgent plea to save humanity’s closest biological relatives, saying scores of different species of apes, monkeys and other primates are all now facing “impending extinction”.

Despite gorillas, orangutans and lemurs being among the most popular wild animals, a factor that helps fund conservation efforts, their main threats are almost entirely caused by human beings.

Primates are hunted for meat and body parts or captured for life as pets; their habitats are destroyed as industrial-scale farms to make foodstuffs like palm oil take over previously wild land, dams are built or mining, oil and gas companies move in; and new threats like climate change and the spread of human diseases to animals are also emerging.

Of the 504 primate species, about 60 per cent are threatened with extinction and 75 per cent have declining populations.

However, the researchers, who published the findings of a major review of primates in the journal Science Advances, insisted they could still be saved.

“Despite the impending extinction facing many of the world’s primates, we remain adamant that primate conservation is not yet a lost cause, and we are optimistic that the environmental and anthropogenic pressures leading to population declines can still be reversed,” they argued.

But they said this would only happen if effective measures were taken “immediately”.

“Unless we act, human-induced environmental threats in primate range regions will result in a continued and accelerated reduction in primate biodiversity,” the scientists said.

“Primate [populations] will be lost through a combination of habitat loss and degradation, population isolation in fragmented landscapes, population extirpation by hunting and trapping, and rapid population decline due to human and domestic animal-borne diseases, increasing human encroachment, and climate change.”

They said that “perhaps the starkest conclusion of this review” was the collective failure to preserve primate species and their habitats.

“We have one last opportunity to greatly reduce or even eliminate the human threats to primates and their habitats, to guide conservation efforts, and to raise worldwide awareness of their predicament,” the researchers added.

“Primates are critically important to humanity. After all, they are our closest living biological relatives.”

Animals in decline Show all 8 1 /8 Animals in decline Animals in decline Harbour seal (Phoca vitulina) Where: Orkney Islands. What: Between 2001-2006, numbers in Orkney declined by 40 per cent. Why: epidemics of the phocine distemper virus are thought to have caused major declines, but the killing of seals in the Moray Firth to protect salmon farms may have an impact. Alamy Animals in decline African lion (Panthera leo) Where: Ghana. What: In Ghana’s Mole National Park, lion numbers have declined by more than 90 per cent in 40 years. Why: local conflicts are thought to have contributed to the slaughter of lions and are a worrying example of the status of the animal in Western and Central Africa. Animals in decline Leatherback turtle (Dermochelys coriacea) Where: Indonesia, Malaysia, Mexico, Costa Rica. What: Numbers are down in both the Atlantic and Pacific. It declined by 95 per cent between 1989-2002 in Costa Rica. Why: mainly due to them being caught as bycatch, but they’ve also been affected by local developments. Alamy Animals in decline Wandering albatross (Diomedea exulans) Where: South Atlantic. What: A rapid decline. One population, from Bird Island, South Georgia, declined by 50 per cent between 1972-2010, according to the British Antarctic Survey. Why: being caught in various commercial longline fisheries. Alamy Animals in decline Saiga Antelope (Saiga tatarica) Where: Kazakhstan, Mongolia, Russia, Turkmenistan, Uzbekistan. What: fall in populations has been dramatic. In the early 1990s numbers were over a million, but are now estimated to be around 50,000. Why: the break up of the former USSR led to uncontrolled hunting. Increased rural poverty means the species is hunted for its meat Animals in decline Swordfish (Xiphias gladius) Where: found worldwide in tropical, subtropical and temperate seas. Why: at risk from overfishing and as a target in recreational fishing. A significant number of swordfish are also caught by illegal driftnet fisheries in the Mediterranean Animals in decline Argali Sheep (Ovis mammon) Where: Central and Southern Asian mountains,usually at 3,000-5,000 metres altitude. Why: domesticated herds of sheep competing for grazing grounds. Over-hunting and poaching. Animals in decline Humphead Wrasse (Cheilinus undulatus) Where: the Indo-Pacific, from the Red Sea to South Africa and to the Tuamoto Islands (Polynesia), north to the Ryukyu Islands (south-west Japan), and south to New Caledonia. Why: Illegal, Unregulated and Unreported (IUU) fishing and trading of the species

Professor Paul Garber, of Illinois University, who co-led the study with Alejandro Estrada of the National Autonomous University of Mexico, emphasised how lose extinction was for some iconic species.

“This truly is the eleventh hour for many of these creatures,” he said.

“Several species of lemurs, monkeys and apes — such as the ring-tailed lemur, Udzunga red colobus monkey, Yunnan snub-nosed monkey, white-headed langur and Grauer's gorilla — are down to a population of a few thousand individuals.

“In the case of the Hainan gibbon, a species of ape in China, there are fewer than 30 animals left.”

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The critically endangered Sumatran orang-utan lost 60 per cent of its habitat between 1985 and 2007, Professor Garber added.

And he said at times humans were exploiting forest habitats “in needlessly destructive and unsustainable ways”.

The biggest problem was the increasing amount of land being used for farming.

“Agricultural practices are disrupting and destroying vital habitat for 76 percent of all primate species on the planet,” he said.

“In particular, palm oil production, the production of soy and rubber, logging and livestock farming and ranching are wiping out millions of hectares of forest.”

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And that meant many primates were now “clinging to life” in the forests of China, Madagascar, Indonesia, Tanzania, the Democratic Republic of Congo and other countries.

“Sadly, in the next 25 years, many of these primate species will disappear unless we make conservation a global priority,” Professor Garber said.