The most recent census of mountain gorillas in Uganda's Bwindi Impenetrable National Park--one of only two places in the world where the rare gorillas exist--has found that the population has increased by 6 percent since the last census in 2002, according to the Uganda Wildlife Authority, the Wildlife Conservation Society, the Max Planck Institute of Anthropology and other groups that participated in the effort.
"This is great news for all of the organizations that have worked to protect Bwindi and its gorilla population," said Wildlife Conservation Society researcher Dr. Alastair McNeilage, who is also the director of the Institute of Tropical Forest Conservation in Bwindi. "There are very few cases in this world where a small population of a endangered primates is actually increasing."
According to the census, which also successfully used for the first time genetic samples from fecal specimens, Bwindi's gorilla population now numbers 340 individual gorillas, up from 320 in 2002, and 300 in 1997.
The census was conducted between April and June 2006 to determine the size and makeup of the Bwindi population, in addition to their distribution and to gauge human impacts on the gorillas. During that time, survey teams set out with the intention of counting every family group in the population, a method possible only with small animal populations in a relatively small area; Bwindi Impenetrable National Park is approximately 127 square miles in size.
In addition to census methodologies such as counting trails and nests (gorillas construct a nest each night), researchers used genetic analyses as well, specifically because many of the groups were clustered in the same area of the park, which presented survey teams with the risk of double-counting the same individuals or groups. DNA analysis, however, allowed individuals to be identified and distinguished, even among groups which have never been seen by people. Fecal specimens were analyzed at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.
Researchers were encouraged by the overall growth of the population, showing an annual increase of one percent over the past decade. The age composition of the population shows a healthy distribution of adult and immature classes, including infants and juveniles. Other findings are that gorillas are not using the eastern side of the park, a possible result of human disturbances there. Particularly encouraging, however, is that one group of gorillas are starting to use the northern sector of the park for the first time in living memory.