I agree with the comments about Whipsade's chimps, and feel they should either reinvigorate the group somewhat (on welfare grounds), or relocate them into an existing group elsewhere.
I realise the words are interchangeable, but I think of static, ageing small groups as 'chimps', but when seen in a dynamic and socially cohesive troop I see 'chimpanzees'. It would be very gratifying to see research into the differing levels of association and social organising in various captive groups of this species, with some kind of a benchmark for optimum activity levels. Its one thing to provide food-based enrichment but, as many on here have stated, there is a world of difference between a group of six adults and a breeding group of 20+ individuals. I think it is wrong to prevent all breeding in certain species, when limited breeding can still prevent a population increase but maintain a good intergenerational balance. I think it is a shame that the UK or European population is managed genetically rather than socially (in terms of pure/generic, not in terms of inbreeding), and I think it would be wrong for ZSL to just hold these last individuals as they gradually die out. Maybe the example to be followed here is Chester or Edinburgh.
Additionally, if groups are allowed limited breeding but with the intention of reducing numbers still over time, then this presents a case for combining remaining groups at strategic points, difficult as this may be it is achievable. I suspect that Whipsnade, Dudley, Twycross and Colwyn Bay don't really intend to hold their chimps long-term, but that is still an awful lot of years in which these individuals will be slowly ageing in ever dwindling groups. I don't think that's an ideal way for a zoo chimp to grow old, and ultimately results in situations such as Drayton Manor or Africa Alive, where solitary individuals are argued as being too old to relocate. Its strange to consider that in 2014 we have chimps living on their own in the UK. I suspect ZSL may even be planning an eventual relocation of the chimps, but are possibly unable to do so until certain dominant or elderly individuals have passed away if any are deemed too risky for moving/introduction into a new group. Of course, I very much doubt anywhere without an existing group would ever take them and, politically, there's no way any facilities associated with 'rescue' would be considered. Blair Drummond is a very interesting case, as they are the only example in recent years of a collection willing to absorb the remaining individuals of a defunct non subspecific group (from Flamingoland) that I am aware of. Prior to this it would have been Dudley perhaps?