AFAIK you are correct. As I said in my post, I did not see Leia or Tuan on my visit this week. I presume Tuan is still in the old Ape House and that Leia was out of sight, either among the plants in the outdoor enclosure or in the off-show chutes or den areas (which they used to give the Sumatrans free access to, so again I presume the same applies to the Borneans).
At the moment, all except Tuan run together and they can use all 3 indoor enclosures and the larger open-topped outdoor one - I am not sure if they actually have access to the other open-topped enclosure (overlooking the Aquarium) at the moment but they could easily be given it. The 2 netted enclosures that the Borneans previously used are empty and I don't know how they may be used in future.
The zoo could hold extra orangs now, as they did with ones from Blackpool, but the long-term plans will depend on the future of the old Ape House. If it is demolished completely they will need to provide some alternative accommodation for Tuan.
If anyone can enlighten us further, please do so.
I don't think that the soil eating problem can be cured.
I suppose it would be possible to house Tuan in the first of the three indoor areas in RotRA, without access to the planted outdoor enclosures. I don't know if the new bark flooring would be a problem for him or not, but I am sure there are alternatives. He could have outdoor access in the adjoining netted area, but that would certainly require modification: perhaps a gravel floor would be a better alternative than concrete.
On the other hand, if the zoo were going to do this, they could have started already. Perhaps they are concerned by the way that Tuan might react to being on-show again and to the other changes involved. Perhaps they are worried how Willie and Martha might react to his presence.
I don't think that the demolition of the old Ape House is an immediate priority. If the zoo continues to attract visitors in large numbers this year, I expect that once the current work on Cafe Bemba and the aye-aye exhibit is completed, the next projects will involve more upgrading of visitor facilities and then the completion of the current phase of Islands *touches wood*.
Alan
One further thought occurs to me. If Willie is doing his duty, Leia and Sarikei will fall pregnant again soon, if they have not already done so. This means that Willie and possibly Iznee will eventually need to be separated from them, which would really stretch their resources of space if Tuan were also on-show in RoTRA. I had overlooked this factor because I am so used to the 'happy families' approach used for the Sumatrans there.
