DNA tests suggest mountain gorilla population 'shrunk'

One of the most endangered species of gorillas could be in greater peril than previously thought.

Kate Devlin, The Telegraph 21 Jan 09;

Experts could have to scale back their estimates of how many mountain gorillas are left in the wild after a new survey cut numbers in one of their main habitats.

Only around 700 of the gorillas still live in the wild after years of uncontrolled hunting, destruction of their forest habitat and illegal capture as pets.

Traditionally researchers have estimated the species population by counting the number of 'nests' which the animals build.

According to this method, there are 336 gorillas left in the Bwindi Impenetrable National Park in Uganda.

However, DNA tests on the animals' dung show that counting nests could be inaccurate and that there are far fewer mountain gorillas in the park than previously thought.

The scientists found just 302 separate genetic codes, suggesting that some of the animals create more than one nest, the findings, reported in New Scientist magazine, show.

Katerina Guschanski, from the Max Planck Institute for Evolutionary Anthropology in Liepzig, Germany, who led the new study, said: "We assumed that each individual constructs a single nest, but genetic analysis shows that several individuals construct more than one nest."

Previous studies of other species of gorilla have shown that they can build more than one nest if the original develops problems, such as leaking.

Conservationists had previously thought that the number of mountains gorillas in the Bwindi national park, one of only two places in the world where gorillas still live in the wild, had been growing.

There were just 300 of the animals left in 1997 but a census in 2003 found 320.

"Now we don't really know what is happening with this population," said Guschanski. "Probably the safest thing is to assume that the population is stable, but we will need to wait for another four to five years to assess how it is changing."

Researchers believe that only an accurate idea of population numbers can help prevent the species from becoming extinct.

"It is much better to have an accurate estimation of the population", said James Burton from the Earthwatch Institute in Oxford.

"Knowing whether it is increasing or decreasing governs the conservation activities."

The other main habitat for the gorillas is Virunga National Park in the Democratic Republic of Congo, thought to contain an estimated 380 animals.

Scientists believe that this figure could be more accurate as the gorillas there are more accustomed to human contact and scientists have been able to get closer to count numbers.

The mountain gorilla belongs to the Eastern Gorilla family, of which there are around 16,000 in the world.

The other family, Western Gorilla, has around 350,000 members, but both are considered endangered.