An impressive male Proboscis Monkey. As we sailed along the Sekonyer River in Tanjung Puting National Park (Indonesian Borneo) we spotted a male Proboscis Monkey sitting on an exposed branch over the river. These are very striking and impressive monkeys. The proboscis monkey or long-nosed monkey is an arboreal Old World monkey with an unusually large nose, a reddish-brown skin colour and a long tail. Theories for the extensive length of their nose suggest it may be sexual selection by the females, who prefer louder vocalisations, with the size of the nose increasing the volume of the call. An amazing monkey.