Is this group reproducing at all, or is it simply fading away? There's something rather sad about the idea of a species such as this - and the various other mangabeys and guenons - slipping away from the world zoo scene.
Interestingly, I've just noticed since posting this that according to Zootierliste there is a single individual in the unlikely-sounding Sochi Monkey Nursery, so they may not be unique.
Photo reminds me rather of the rare Golden-bellied Mangabey pair at Port Lympne which I saw again just a month or so back,- they have never bred since they have had them- the male is very geriatric, (if he's still alive) and no further animals have ever been added to try to promote breeding-a problem in obtaining more animals or a lack of interest after getting them initially? A bit of both I suspect.