I've always anticipated Striated as a potential species for HK and check any Red-rumped. When they started breeding at Kam Tin, I looked carefully at the birds hoping that they would be Striated. I think the most field guides suggest they are more easily separable than is actually the case in this part of the world. This presumably results from unfamiliarity of most observers with the Chinese races which are most similar to each other. Subspecies elsewhere are very different and, like Paul, I suspect there may be hidden species in this complex.
For what it's worth, when I saw striated in the Philippines it struck me looking rather different from HK birds, seeming larger and bulkier, but I don't know to what extent this was due to context. Plumage differences were difficult to pick up in the field.
