Very interesting - after a bit of research I believe these are Sciurus lis - a very rare exhibit species (though around in the pet trade according to Google!). Zootierliste only lists one other European collection with them.
Are you sure they're not Sciuris vulgaris - which, according to Zootierliste, are in four places in Europe. One of these, bizarrely, is the Reserva Africana in Mallorca. Another is the Spaycific Zoo, near Le Mans, where I saw them in the summer.
If they are Sciuris lis, Isis has them listed as only being at Ueno Zoo in Tokyo. So what are they doing at a place whose name alone marks it out as being dreadful: "Wingz" indeed - what is the world coming to?
Unfortunately if you Google 'Japanese White-bellied Squirrel' it mostly goes to pet websites, where trying to find a scientific name is an impossible task - though the pet trade activity does explain how a small collection has access to them. nb123, are they labelled with a scientific name?
From what I could see on t'Internet, Japanese vulgaris seemed much more reddish (like UK individuals), but the Zootierliste picture does match this animal much more closely. Nice animal, either way.
I have seen some extremely dark-coloured wild red squirrels in Spain.In Soria I saw one individual who looked almost black.As always, European species are among the least-studied and least-understood on the planet, although hopefully the situation will improve in line with the changing sensibilities & research priorities of new generations of zoologists.
