Ok, I will take your word for that, I can`t recall them being labelled as anything other than just Douroucouli, of course back then that was mostly the case.
I'm quite interested in these animals, Dave, and would be keen to know why you think they are Humboldt's.
For the year this picture was taken (1990), the ZSL annual report lists only 'Dououcouli', to which it ascribes the scientific name Aotus trivirgatus bolivensis., rather than the name one might now expect (Aotus azarae boliviensis).
By 1994, it was calling them 'Douroucouli (Bolivian)', and using the same scientific name.
In the same year, a pair of simple 'Douroucouli' joined the collection, with Aotus trivirgatus given as the scientific name.
The 'Bolivians' left the collection in 1996, and the following year the other animals were 're-branded' as Aotus lemurinus griseimembra (the grey-legged - although ZSL did not use this term until 2000).
So, by that reckoning, in recent years the zoo has had, first Bolivian, then grey-legged, but not Humboldt's. Unless anyone knows different! (trying to untangle the occasionally rather nebulous annual reports is quite a mission, sometimes).
My statement was based on the fact that ZTL lists both Humboldt's and Bolivian at London during this time - presumably, from what you say, interpreting the mention of trivirgatus to refer to the true taxon rather than the pre-split larger classification - and to my eye these animals did not look like the Bolivians I have seen in the past at Tropical World and Zoo Berlin.
Which is actually quite amusing in retrospect, as one of the Bolivians at Tropical World *is* one of the old London animals, and thus quite likely is in this photograph!
I'm quite interested in these animals................trying to untangle the occasionally rather nebulous annual reports is quite a mission, sometimes).
As I am sure you all know, the problem is that years ago Douroucoulis were simply labelled as that. (The same goes for many, many other species too of course) Only in more recent years have zoos decided to split them into sub-species and label them accordingly. Strangely enough, even Marwell itself, who run the studbook through Shelly Parkes, as Tim rightly says, initially referred to them as just Douroucoulis when they first arrived, it was only afterwards when the studbook was administered by Marwell did they actually come out and say they were Grey-legged! So I think it is very easy to be confused about them as a whole. The differences between the sub-species are not always obvious in a species which rarely shows itself in daylight.
