Siamangs

Siamang's are also lesser apes. Their arms are twice the length of their body and they are the largest gibbons. Like the white-handed gibbon this species can walk upright among the branches with its arms stretched out for balance. The gibbon can leap 30 feet to another branch quickly. The siamangs are a close family usually staying with 30 feet of each other at all times are rarely more than 100 feet apart. Underneath the chin is an inflatable throat skin that the siamangs use to increase or amplify the volume and distance of their duets. Each siamangs has a distinct voice and while they are performing they also do acrobatic moves through the trees. This special duet can be heard every day mid-morning at the Zoo, and you don't have to be next to the exhibit to hear it, the sound travels for more than a mile.

Information from:http://www.miamimetrozoo.com/map2.htm