That tree is 15 years out of date yet still proudly displayed ! I actually like info like this where family connections between animals held are explained but only where it's relevant .... and it does seem to contradict somewhat with the few colobus still there (as Bele said). From memory (I might be imagining this) I think there's also some additional written info there about how successfully the colobus have bred, which again doesn't quite ring true these days.
Yes, I've often noticed it and the fact its well out of date now. I think it might be time to take it down?
Colobus breed freely(like flies almost) in many Zoos so it is hardly a major achievement for them, but that's not to decry their past success with them. I rather wish they would concentrate on keeping just a few large thriving groups of their simpler-to- breed primates e.g. Colobus, Langurs etc if they cannot achieve anything with many of the other more difficult/shyer species, particularly the Guenons.
The sign can't possibly be fifteen years out of date, as there is at least one date on there from 2005. I guess they must not have updated it over the last few years, when did they last breed them?