Bwindi Impenetrable National Park in Uganda is one of the last places where mountain gorillas still live in the wild, a dwindling redoubt in the last decades of the 20th century. But a new census shows that gorillas there have been making a comeback since the government began protecting the mountainous forest in 1991, dramatically limiting logging, hunting and other human activities that cut into their population. The most recent census of its small mountain gorilla population shows that they are continuing to thrive: up from just 300 in 1997 to 340 in 2006. "In Bwindi, which is one of only two populations of mountain gorillas [left in the world], there seems to be a continued small increase," says Alastair McNeilage, a research ecologist at the Wildlife Conservation Society, who worked on the census.

The researchers surveyed the 127-square-mile park in several teams in search of gorilla trials. They then followed the trails to the gorillas' evening nesting sites; they used the nests (gorillas construct a new one each night) to gauge the size of the population. "You can follow the trail and count the nests and work out how many individuals are in that group," McNeilage says. "Size of the nest, size of the dung and the presence of silver hairs can tell you quite a lot about the group."

Researchers used genetic analyses of the gorilla dung left behind to determine the individual identities of overlapping groups. "There was one corner of the park where, by coincidence, there were three or four groups all overlapping. If we were just looking at the trails, we would have thought there were one or two groups," McNeilage says. "But looking at the genetics, we could identify four different groups." Ongoing research is surveying the flow of genetic material through the population, the true habitat requirements of the gorillas as well as how to create buffer zones between them and the surrounding humans.

Even though the population is showing signs of growth, it is still perilously small, putting it at risk of disease outbreaks or other threats, meaning the gentle giants are not safe in the woods yet. "There are a number of things that could happen just because it's a small, vulnerable population," McNeilage says. But "we're fairly hopeful that the upward trend will continue."