Flying squirrels of various species, varying in size from the tiny ones in North America and Russia to giant (Grey Squirrel-sized) species in tropical Asia can be found in many forests but I do not think I have ever seen an exhibit of one. Has anyone here ever seen a flying squirrel exhibit and how did it work out? As a group there are not many tree squirrels to be seen in zoos considering how iconic they are as forest animals.
I've seen the smaller American and Siberian in nocturnal exhibits in several zoos and that works fine. Same for the superficially similar gliding marsupials: sugar glider, feather-tailed glider. The giant Asian are considerably larger than a grey squirrel. I've seen red-and-white giant, Indian giant and red giant in zoos, but their exhibits rarely work well (typically either diurnal exhibits [flying squirrels are nocturnal] or too small to really show their behavior). The one exception is the giant flying squirrel exhibit at Singapore's Night Safari, which basically is a large netted walk-through enclosure and IMO one of the highlights of the place. Check the Singapore Night Safari gallery on this site or search giant flying squirrel night safari on youtube for some videos.
In Europe it seems the most common practice for the smaller species (Southern and European) is to just keep them like you would keep any other small rodent; in a glass-fronted terrarium with a few climbing possibilities and nest boxes, but without any place for them to glide (which I'm not sure they really need in captivity, either). An interesting species I've seen them combined with is Hispid cotton rat, with the Southern flying squirrel in Plzen's Sonora house. With the larger species you can do more, though. Wroclaw keeps red-and-white flying squirrels together with echidnas in a nocturnal indoor enclosure that has access to an outdoor aviary. I'm not sure if they also have access to the aviary at night, but I do assume so as otherwise I don't think the squirrels would use it. The indoor area there is not the biggest, but I suppose can show a very short amount of "gliding" when they jump down from their nest box. In Gembira Loka Zoo a single red giant flying squirrel is housed in a diurnal outdoor cage, where gliding is impossible and where I only saw it sleeping. As @temp mentioned, the most impressive enclosure for flying squirrels is, without a doubt, that of red-and-white and Indian giant flying squirrels in the Night Safari, where you walk through their exhibit and where they are encouraged to do a very short "glide" from the trees surrounding their indoor enclosure/nest box to the trees in which they are fed. On my visit these were combined with the very rare yellow-striped mouse deer, that had an enclosure within their aviary.
The only time I've seen one was at the Oklahoma City Zoo. They had a couple of southern flying squirrels in the "Creatures of the Night" section (an indoor nocturnal house obviously) of the Oklahoma Trails exhibit. It was a fairly big space for such a small animal, more vertical than horizontal, but clearly not enough room for a glide. "And now..." "Hey, Rocky! Watch me pull a rabbit out of my hat." "Again?!"
In Bay Beach Wildlife Sanctuary's Woodland Building, there is a nocturnal exhibit for Southern Flying Squirrel and Eastern Cottontail. It is very good, with lots of room to climb and lots of places to hide (I visit at least once a years and have only seen it a few times). That is the only captive flying squirrel I have seen.
Riga Zoo actually has them (Siberian flying squirrels) in a "regular" squirrel aviary (no night exhibit and no glass-fronted exhibit). Of course they were no-shows. Same with Dresden Zoo where I also didn't see them. I haven't come across a night exhibit yet, so I've never seen a flying squirrel. As for tree squirrels, I find that many zoos keep them, but now that you mention it, they do seem to be much easier to find in small, privately-owned collections (probably because many squirrel species are kept and bred in private hands) and underrepresented in major zoos (with the exception of Prevost's squirrel).
