In a remote region in the north of the Congo scientists discovered an unknown population of Eastern chimpanzees. Like all natural ape populations poaching is a major threat. Credit: Ephrem Mpaka, Lukuru Wildlife Research Foundation

(Phys.org) —With great ape populations in fast decline, it is crucial to obtain a global picture of their distribution and abundance, in order to channel and direct conservation activities to where they are most needed. Researchers of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, and the University of Amsterdam in The Netherlands conducted hundreds of kilometers of chimpanzee surveys at multiple sites in the Central Uele region of northern Democratic Republic of the Congo and discovered a large, continuous population of Eastern chimpanzees (Pan troglodytes schweinfurthii). The population in the remote Bili-Gangu forest was surveyed in 2005 with line transects and again in 2012, and appears to have remained stable. The total area surveyed, which encompasses about 50,000 square kilometers, is home to several thousands of chimpanzees and, according to the researchers, should be considered a priority site for conservation of the eastern subspecies.

Over the past two decades the African great apes have experienced a steep population decline, up to 90 percent in some regions. This has been a result of expanding agriculture in many African countries, as well as logging and the uncontrolled extraction of natural resources. Furthermore, chimpanzees often fall victim to poachers and are killed by human diseases. "In order to monitor chimpanzee population trends and to decide where to best allocate conservation resources, it is crucial that we develop the means to accurately map the species' distribution and make precise estimates of abundance", says Hjalmar Kuehl of the Max Planck Institute for Evolutionary Anthropology. In order to determine the chimpanzee population size in an area the researchers traverse it at regular intervals along parallel line transects. From the existing number of chimpanzee sleeping nests they can then estimate the total number of chimpanzees in this area.

From 2004 to 2012, a research team from the Max Planck Institute for Evolutionary Anthropology and the University of Amsterdam conducted chimpanzee surveys in the north of the Democratic Republic of the Congo, a region where chimpanzee populations have never previously been systematically assessed. They covered a total of 1,800 kilometers of reconnaissance walks to the north and 500 kilometers to the south of the Uele River as well as 160 kilometers of line transects in the Bili-Gangu Forest, and discovered a population of chimpanzees numbering in the thousands. Evidence of behavioral continuity shows that the north and south groups may be connected culturally as well. "Our results suggest that a large and widespread population of chimpanzees inhabits the forests and savannas of northern DRC", says Thurston C. Hicks. "This population has remained unnoticed to researchers until now and may represent the largest viable population of this subspecies, but it currently lacks any protection." When they re-walked parts of these transects again in 2012, the researchers found that the number of chimpanzee sleeping nests had not declined since 2005.

While this chimpanzee population has remained stable over the last decade, the researchers have recently found signs that it is falling under increasing threat from the bush meat trade. "Increasing numbers of bush meat carcasses and chimpanzee orphans were found in Bili and nearby areas", says Christophe Boesch, director of the Department of Primatology at the Max Planck Institute for Evolutionary Anthropology. "Without proper protection these chimpanzees may succumb to the same factors that are eliminating populations of the species elsewhere". According to the researchers additional field survey projects will need to be conducted so that future conservation activities can be directed to areas where they are most needed – before it is too late. It is recommended that wildlife guards be installed permanently in the region to avoid an escalation of poaching.

"Bili-Gangu's diverse mosaic of closed forest, wooded savannas and open grasslands, with its populations of chimpanzees, elephants, leopard and other large mammals, rare or extirpated elsewhere, represents one of Congo's most important opportunities for the establishment of a new conservation initiative within the Bili-Uéré complex", says John Hart of the Lukuru Wildlife Research Foundation.

More information: Thurston C. Hicks, Sandra Tranquilli, Hjalmar Kuehl, Geneviève Campbell, Jeroen Swinkels, Laura Darby, Christophe Boesch, John Hart, Steph B.J. Menken. "Absence of evidence is not evidence of absence: Discovery of a large, continuous population of Pan troglodytes schweinfurthii in the Central Uele region of northern DRC." Biological Conservation, 05.02.2014, Journal information: Biological Conservation Thurston C. Hicks, Sandra Tranquilli, Hjalmar Kuehl, Geneviève Campbell, Jeroen Swinkels, Laura Darby, Christophe Boesch, John Hart, Steph B.J. Menken. "Absence of evidence is not evidence of absence: Discovery of a large, continuous population of Pan troglodytes schweinfurthii in the Central Uele region of northern DRC.", 05.02.2014, DOI: 10.1016/j.biocon.2014.01.002