Female Mang, who was born on 21 October 1988 at San Francisco Zoo, arriving at Adelaide Zoo in 1997, is the most dominant in the group and calls all the shots. Reckon I would do as she says with a mouth like this. The Siamang have a ritual territory calling each morning and it doesn't matter where you are in the zoo you will hear their call - Calls are harsh barks and shrieks, punctuated by the boom from the throat sac which both sexes possess, that swells when calling. The throat sac acts as a resonating chamber t o amplify and carry the call.