Few viable populations of western black crested gibbon Nomascus concolor remain in southern China and northern Indochina, where the species is endemic. We conducted village surveys in the Nam Ha National Protected Area in Luang Namtha Province, Lao PDR to assess presence and status of gibbon populations. Forest surveys used to verify gibbon presence and species identification confirmed village reports of gibbon populations in three locations, and sonogram analysis identified all as N. concolor. These represent an expansion in the known distribution of western black crested gibbon in Lao PDR and the only known populations to occur inside the national protected area system. Significantly longer times since gibbons were last reported were associated with villages with <50% forest cover and high human populations. Although village taboos regarding gibbon hunting were reported, hunting and trade were nevertheless identified as factors contributing to gibbon decline. Results indicated that increased community-based management, public education and enforcement are needed to maintain N. concolor populations and their habitat in Lao PDR.

Unlike the great apes and most other primates, all species of gibbons are known to produce elaborate, species-specific and sex-specific patterns of vocalisation usually referred to as “songs”. In most, but not all, species, mated pairs may characteristically combine their songs in a relatively rigid pattern to produce coordinated duet songs. Previous studies disagree on whether duetting or the absence of duetting represented the primitive condition in gibbons. The present study compares singing behaviour in all gibbon species. Various vocal characteristics were subjected to a phylogenetic analysis using previously published phylogenetic trees of the gibbon radiation as a framework. Variables included the degree of sex-specificity of the vocal repertoire, the occurrence of solo songs, and the preference for a specific time of day for song-production. The results suggest the following scenario for the evolution of gibbon songs: (1) The last common ancestor of recent gibbons produced duet songs. (2) Gibbon duets probably evolved from a song which was common to both sexes and which only later became separated into male-specific and female-specific parts (song-splitting theory). (3) A process tentatively called “duet-splitting” is suggested to have led secondarily from a duetting species to a non-duetting species, in that the contributions of the pair-partners split into temporally segregated solo songs. This appears to be the first time that a non-duetting animal can be shown to be derived from a duetting form. (4) The return to exclusive solo singing may be related to the isolated island distribution of the non-duetting species.