Our Trekkers visit the last strongholds of many rare and sometimes endangered species of primates. Justine Shapiro heads to Thailand in search of the White-Handed Gibbon. Holly Morris, Ian Wright and Megan McCormick get up close and personal with the orangutan in Borneo and Sumatra, the chimpanzee in Tanzania and Zambia and the Mountain Gorilla in the remote mountains of Uganda. Ian glimpses the elusive Golden Bamboo Lemur on Madagascar, Eils Nevitt discovers the Black-Crowned Dwarf Marmoset - at six inches high, the world's second-smallest monkey - in the Amazon jungle and Zay Harding encounters two enormous and extremely rare apes in Africa: the Drill in Cameroon and the Mandrill, known as the world's largest monkey, in Gabon.