Science Daily reports that the 14-member scientific team recently carried out a survey in all Chinese forests. They could not locate a single Yunnan white-handed gibbon. The last time this ape was observed in China was in 1988 at the Nangunhe Nature Reserve in south-western Yunnan province. Their loud, melodious calls were last heard in 1992. This subspecies (Hylobates lar yunnanensis) is not known from any other place.
Luckily, these apes are not lost to us forever. Several zoos have included them in their programs. One is the Honolulu Zoo. On their web page, you can hear the call of the white-handed gibbon:
listen
You can also see pictures of Emma, an adorable baby white-handed gibbon, born in 2000. Here's a picture of Emma, 7 hours after birth.