A new survey shows Africa's critically endangered mountain gorillas have exceeded 1,000 after conservation efforts, making them the only great ape in the world considered to be growing in number.

Gihishamwotzi, 18, an endangered silverback high mountain gorilla from Sabyinyo family, rests atop trees inside the forest in the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018.
Gihishamwotzi, 18, an endangered silverback high mountain gorilla from Sabyinyo family, rests atop trees inside the forest in the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018. (Reuters)

The population of mountain gorillas, one of the world's most endangered species, which survives on the forest-cloaked volcanoes of central Africa, has increased by a quarter to over 1,000 individuals since 2010, wildlife authorities said.

That is despite the threat posed by poachers and armed groups in the Virunga Massif, a spine of volcanic mountains in the western Rift Valley straddling eastern Democratic Republic of Congo, Uganda and Rwanda, where most of them reside.

An endangered baby high mountain gorilla from the Sabyinyo family plays inside the forest within the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018.
An endangered baby high mountain gorilla from the Sabyinyo family plays inside the forest within the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018. (Reuters)

The latest census put them at 1,004 individuals: 604 in Virunga, and 400 in Uganda's nearby Bwindi Impenetrable National Park, Joel Wenga Malembe, spokesman for the Congolese Institute for the Conservation of Nature, told Reuters.

The last survey, in 2010, found just 786 of this critically endangered eastern gorilla sub-species, of which 480 were in Virunga.

Park wardens are seen in the forest as they track the high mountain gorillas from the Sabyinyo family, within the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018.
Park wardens are seen in the forest as they track the high mountain gorillas from the Sabyinyo family, within the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018. (Reuters)

"These numbers are truly remarkable, far exceeding our expectations, and are the result of a collaborative, three-country effort with governments and partners all playing an important role," Mike Cranfield, of charity Gorilla Doctors, said in a statement.

Partly because they are so rare, the mountain gorillas are a major source of tourist revenue for the three nations, and their habitat supports other rare species found nowhere else such as golden monkeys.

But they are under constant threat of encroachment by farmers in one of Africa's most densely populated rural regions, and hunting for bush meat or bizarre trophies sold abroad.

Endangered high mountain gorillas from Sabyinyo family play inside the forest within the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018.
Endangered high mountain gorillas from Sabyinyo family play inside the forest within the Volcanoes National Park near Kinigi, northwestern Rwanda, January 9, 2018. (Reuters)

Congo has also invited oil companies to start drilling in Virunga, Africa's largest tropical rainforest reserve, which conservationists worry will put the environment in greater danger.

Adding to Virunga's woes, rangers banned tourists this month from entering the park during investigations into the kidnapping of two Britons by an armed militia.

Source: Reuters