For your future reference, the easiest ways to separate Eurasian Collared Dove from Red Turtle Dove are size, structure and tail pattern.
- Red Turtle Dove is tiny - it often looks almost as small as a starling - while Eurasian Collared Dove is much larger, slightly bigger than a Spotted Dove. - Red Turtle Dove is fairly short tailed, whereas Eurasian is longer-tailed, again looking structurally more like Spotted Dove.
- The tail pattern of Red Turtle Dove (when seen in flight) looks like the tail is surrounded by white, with an even fringe of white around the tip of the tail (
http://orientalbirdimages.org/se ... e_ID=55631&p=25). On Eurasian, the tail usually looks like it has large white 'corners' with little white on the inner tail feathers and the white of the outer tail is less obvious (
http://orientalbirdimages.org/se ... Family_ID=&p=47). Eurasian Collared Dove has a lot of white on the undertail (at least half of the tail), which is visible on your photo.
- It is also useful to note that the underwing of Eurasian Collared Dove is white, which can be very obvious in flight (
http://orientalbirdimages.org/se ... Family_ID=&p=45)
Typically, Eurasian Collared Dove in the field looks like a larger, paler bird than Red Turtle Dove. Once you are familiar, this is easy to recognise in the field (much easier than looking in detail for the colour of the iris!)
You've done some good research on subspecies. I think, though, that the Hong Kong population only contains
decaocto. Some birds may show a hint of yellow in the orbital ring, as on your bird, but I think the critical differences between the two are the width of the orbital ring and the intensity of the yellow - compare this
xanthocycla from Myanmar:
http://orientalbirdimages.org/se ... _ID=&pagesize=1 . Birds like this certainly don't seem to be present in Hong Kong.
