There does seem to be a nice bond forming between Melur and Daya. Possibly it's because of Daya's gentle nature and because she tends to respect Melur's space and acknowledges Melur as the dominant female - Wanita and Gangsa were more dominant personalities and from what I've heard, Melur tended to defer to Wanita and came into conflict on occasion with her half-sister, Gangsa.
The five females (Indra, Intan, Wanita, Melur and Gangsa) cohabited from the arrival of the Taronga females in 2001 until 2005. It appears this was out of necessity as the separation annex (used to house the male not on rotation) was at most big enough for two orangutans. A better approach would have been to house the two adult males (Horst and Charlie) with 2-3 females each and indeed the departure of the chimpanzees freed up their exhibit for them to do this. Following Madju’s birth, the group in the main exhibit was further subdivided into Charlie, Gangsa, Melur (and Madju); and Wanita and Isim. Charlie was presumably assessed as the safer option for housing with the infant; and Wanita was provided to Isim for companionship.
On hindsight, importing Melur alone would have probably worked best. She would have deferred to Indra and a cohesive grouping may have developed long term. Taronga were clearly keen to phase out Bornean orangutans though, otherwise they could have imported Isim into replace Datuk.
I am wondering, though, if perhaps an Australian zoo doesn't become a second holder of Bornean orangutans, if Orana Park is a future possibility? I think that Orana's original plan was to house Sumatran orangutans in one half of the Great Ape Centre, opposite their bachelor gorillas, but that never panned out. That way, Australia could be the regional holder for Sumatrans and New Zealand for the Bornean species.
That would be great to see and in the early 1990’s, was the original plan for management of orangutans within the region. New Zealand would manage Bornean orangutans; and Australia would manage Sumatran orangutans.
Orana Wildlife Park have a spacious great ape facility, but are frequently in the news with regards to financial struggles. Housing a solitary/semi-social species would appear more cost effective than gorillas or chimpanzees, which thrive in larger social groupings.