I know that many males born now are just not going to be used for breeding. So given that experiance todate suggest that the sooner they are placed together the better the chance for long term stability.
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I agree males put together at a younger age are going to get along better and its sometimes very difficult to get strange fully grown males to live together.
One never knows when even a male of low genetic value may not be required to breed- if suppose several group leaders suddenly die around the same time, creating a sudden niche for previously non-breeding males.
I think there may be a move, with contraception, to limit the number of babies(particularly males) produced nowadays as eventually the number of zoos prepared to create bachelor groups will reach saturation point.
Rigo was an unusual case. Have you read the thread 'Rigo the Gorilla' under Melbourne Zoo where many people have written pages about him? Melbourne were in a difficult situation with him for a long time. I agree that no Gorilla, even a 'lone' silverback, should be denied company of some sort- even if its only visual contact of some sort.