Hi Michael, Darrell and all,
Sorry to be lax in getting back here. I wouldn't want there to be any gaps in your knowledge, Michael, so let me say that our feral species in Japan include of course the ubiquitous Rock Dove (or what you may call 'em), the Collared Dove (decaocto, introduced in the 18th/19th C.), Mute Swan, Ring-necked Pheasant, and Chinese Bamboo Partridge. As well, there are breeding Budgerigar and Rose-ringed Parrakeet populations in metro areas (and I would guess some other psittacids as well), and down south Okinawa-way there are half-a-dozen waxbill species merrily reproducing; meanwhile I have personally recorded a steady increase in the Crested Mynah population of Yokohama since 1990.
Which of these would qualify for your feral list, I do not know-- I can't recall having read anything definitive on the status of all of our introduced/escaped species.