In Cambodia, the trees are alive with the sounds of monkeys, according to a recent survey by the Wildlife Conservation Society (WCS). The report reveals surprisingly large populations of two globally endangered primates in one of this Southeast Asian country’s protected areas.

Scientists from WCS together with the Royal Government of Cambodia’s Ministry of Agriculture, Forestry and Fisheries searched an area of 300 square miles within the Seima Biodiversity Conservation Area. They counted 42,000 black-shanked doucs and 2,500 yellow-cheeked crested gibbons. The estimate represents the world’s largest known populations for both species. The researchers believe total populations within the 1,150-square-mile landscape surrounding Seima may be even bigger.

The WCS scientists who worked on the census include Tom Clements, Nut Meng Hor, Men Soriyun, Edward Pollard, Hannah O’Kelly, and Samantha Strindberg.

Prior to this discovery, the largest known populations of the two primate species were believed to live in adjacent Vietnam, where black-shanked doucs and yellow-cheeked crested gibbons number at 600 and 200 respectively. Their total population figures remain unknown.

The Cambodian census took place in a former logging area where the two primates were once extensively hunted. In 2002, the Minister of Agriculture, Forestry and Fisheries declared the region a conservation area and began working with WCS on site management and planning for conservation and local development. In the years since the joint program began, the primates began to recover. Their populations have remained stable since 2005.

The primates have also benefited from a cessation of logging activities, a nation-wide gun confiscation program implemented in the 1990s, and a habitat where there is plenty to eat.

But WCS researchers in Cambodia remain concerned that looming threats could jeopardize recent successes.

“Despite this good news in Cambodia, the area still remains at risk from conversion to agro-industrial plantations for crops, including biofuels, and commercial mining,” said Tom Clements, the lead author of the report. “WCS is therefore committed to continuing to work with the Cambodian government to ensure that these globally important primate populations will remain secure.”

WCS has worked with the Royal Government of Cambodia since 1999, helping to establish the Seima Biodiversity Conservation Area and developing landscape-level conservation programs in the Northern Plains and Tonle Sap Great Lake.

WCS work in Cambodia has been supported by U.S. Fish and Wildlife Service’s Great Apes Conservation Fund, MacArthur Foundation, and Liz Claiborne Art Ortenberg Foundation. The Great Apes Conservation Fund and all the U.S. government funding to support global priority species and their habitats is at risk of being cut in the Fiscal Year 2009 federal budget. Although the budget process in Washington has stalled, WCS is calling for Congress to restore and grow these programs by completing work on the Fiscal Year 2009 budget before the end of September.