You know that a species is in rough shape when a population increase of just 20 animals is cause for celebration. But that's the case in northern Vietnam this month, where one of the few remaining groups of critically endangered Tonkin snub-nosed monkeys (Rhinopithecus avunculus) has grown from just 90 individuals in 2006 to between 108 and 113 today. That's the highest number ever recorded in the Khau Ca Species and Habitat Conservation Area, which now holds about half of the world's population of this rare species. Khau Ca was home to just 30 or 40 of the animals in a decade ago.

Fauna & Flora International (FFI), which surveyed the monkeys with the assistance of local community conservation teams and researchers from the University of Colorado Boulder, says this is a rare case of a critically endangered species in Vietnam reversing its decline. FFI discovered the Khau Ca population in 2002 as well as another small group near the Chinese border in 2008.

Tonkin snub-nosed monkeys were presumed extinct until they were rediscovered in 1989. Today the species, which currently numbers fewer than 250 individuals, can be found in just five fragmented population groups in northeastern Vietnam. It has appeared in every edition of list of the IUCN's "The World's 25 Most Endangered Primates" report (pdf) since 2000. The species remains at risk due to deforestation, illegal hunting and the use of its body parts in traditional medicine.

Photo by Nguyen Van Truong, courtesy of Fauna & Flora International