Monkeys: The use of colourful displays and sound
In Africa there lives de Brazza's Guenon (Cercopithecus neglectus) which has a white beard, blue spectacles, orange forehead and black cap, the Mandrill (Mandrillus sphinx) with a scarlet and blue face, and the vervet monkey, the males of which have startling blue genitals; in China, the Golden Snub-nosed Monkey (Pygathrix roxellana) with a metallic golden coat and an aquamarine face; in the Amazon forests, the Red Uakari with a scarlet naked face (Cacajao calvus). With these colourful displays they advertise and threaten and proclaim both their species identity and their sex.
They also use sound in a similarly extravagant way, for up in the trees they are beyond the reach of most predators. Howler monkeys (e.g. Alouatta seniculus) in South America sit morning and evening, and sing in chorus. Their larynx is extraordinarily large and their throats swell into resonating balloons. The resulting chorus can be heard for several kilometres.