I was captivated by these small, tree dwelling apes. They had so much expression in their faces and they seemed to watch and understand everything that was going on around them. I could have stayed all day just watching and photographing their activities. An unusual fact I learned: Siamangs are native to the island of Sumatra and the Malay Peninsula. Early in the morning, the tropical rain forest usually resonates with "singing" siamangs. Described as a combination of a dog’s bark and a grouse’s hoot, siamangs sing (or call) to communicate between family groups. The sound is produced from an external inflatable throat sac. This sac can be inflated to be as big as the siamang's head. It acts a resonating chamber for the vocal cords, making the sounds even louder. Their hooting can be heard up to 2 miles (3.2 km) away through the dense rain forest.