Whether the inappropriate diet is a reason for langurs populations in zoos do not thrive? Here are included many species, including doucs, proboscis monkeys (as I saw on ZTL they are gone from Europe), Nilgiri langurs (curently only kept in one German zoo - Erfurt Zoopark - but there are about 35 of them in Indian zoos), and others. Is eventual small founders number reason for some species? Yet some species are doing well, like for example Javan lutung (Javan langur) with currently 25 holders in Europe, I don't know for other holders world wide (are there in USA, Japan, Australia&New Zeland...?)
Many langur species are leaf-eaters. Leaves are diffucult to work with, as they usually need to be fresh and if you freeze them you can expect loss of quality (nutrients, structure, taste). Some species are rather choosy, they do not accept every type of leaf as food. So food is definately one of the problems.
Outside Europe, the Javan Lutung is held by Singapore and NY Bronx. François' Langur is kept by many American zoos, as well as in Europe, Japan, China and Australia. Semnopithecus langurs (Hanuman and relatives) do well in captivity, but there is limited interest from zoos in holding them. In fact, other than doucs and Proboscis Monkey, most langurs don't seem to be too difficult to maintain. There have been problems when a relatively small number of founders have produced offspring with a bias towards males...or when Damian Aspinall decides to undo his father's work and send all his Grizzled Langurs back to Java.
Javan luntung may also be held by Henry Doorly (Omaha). It's on their website but I've never seen in listed on ZooChat. Spectacled langurs (Dusky leaf monkeys) came from a small founding population. The US population is all related and quite unlikely to grow. Silvered leaf monkeys (silvery langurs) are on the rise in the USA.
