Among simians, the howler monkey can make one of the loudest calls among animals by inflating the air sacs in its throat. It is not only used for communication, but also as a mating display.
Orangutans have a little-known physical feature – an inflatable pouch along their necks that expands to hold nearly six litres of water! Amazingly, the pouches inflate when the orangutan breathes out rather than in. the sac helps amplify its calls and to climb, breathe and float.
Each social group of howler monkeys consists of 10-20 members organized in a strict hierarchy, with a dominant male as the leader. Group members spend nearly 2/3 of their time sleeping; this is due to the energy-poor diet of the monkeys. Much like the sloth, howler monkeys feed mainly on leaves. This means that they are folivores, or leaf-grazers. These leaves, however, are a poor source of nutrition because most of the calories in the leaves are bound up in hard-to-digest cellulose. To gain a sufficient amount of energy, an adult howler monkey thus needs to ingest more than 15% of its body size per day in leaf matter.
Picture Credit : Google