The species was listed as Common Stonechat on the Hong Kong list until about a year ago, but research has suggested that Siberian Stonechat is a separate species from the birds occurring in Europe. So, this is the same as the birds that were previously listed in Hong Kong as Common Stonechat - only the name is different.
Confusingly, Siberian Stonechat has now also been split, and the form occurring in Hong Kong is named Stejneger's Stonechat - I'm not sure if this change is officially accepted by the Records Committee yet.
I suspect that the darkness of the face on this bird is actually due to the angle of the light. I would expect a male in January to show a more extensively black head (including crown and probably much of the throat), blacker back and more orange underparts. There is also no visible white in the inner greater coverts, which would normally be obvious on a male bird. This looks like a female to me.
