Adelaide seems to be the only zoo in the region truly committed to tamarins; the others are rather half-hearted.
oh... i dunno if thats fair - last i checked it was perth and melbourne keeping the emperor tamarin population alive in australia - not adelaide.
melbourne also have a long and current history of keeping/breeding cotton-tops and golden lion tamarins and are planning on soon adding pygmy marmosets to that list (a species bred by perth and mogo).
i don't think adelaide is any better than any of these above mentioned zoos. i'de say they are all pretty "committed"
emps, cottontops, golden-lions and pygmy marmosets are all being bred with the intention of maintaining the species.
common marmosets are bred at some private zoos and research facilities and are in good numbers, but unfortunately are not being embraced by major zoos. black-lions look destined for a definite phase-out.
i agree it would be nice to keep them all. and i agree wholeheartedly it would take minimal effort compared to larger species. but four definite species, thats more species than most individual zoos keep.