hmmmmm....
i'm confused. the siamangs don't live on an island at melbourne. they share the orangutan exhibit. i didn't know that they had had another baby, but its no surprise if they have.
pat - siamangs, like all gibbons live in family groups very similar to our own. they generally pair for life and adolescents live with parents and younger juvenile siblings. eventually the older offspring are pushed from the group and encouraged to go find mates of their own.
melbourne's siamang pair have only been together for a few years, but fortunately hit it off well from the start producing a female offspring almost immediately. unfortunately she died but soon after they had another, the young male you are talking about. he is still only young himself, so is far from ready to be moved to another zoo. gibbons stay with their parents for a very long time. he will no doubt instead stay at the zoo for now and help in the upbringing of his younger sibling.