[Hong Kong] ID please

On the other hand, for me this bird is not a Saker.
- Head pattern is wrong for me. The mask and moustachial are quite dark, making the eye indistinct. Saker do sometimes show dark moustachial, but on these birds the entire plumage is usually dark, unlike the bird here. The supercilium seems indistinct.
- Underparts show distinct but narrow streaks on the breast and trousers with dark 'arrowhead' markings on the rear flanks. Saker adult typically shows spots (not streaks) on the breast, and is often darker on the underparts than this bird.
- Barring on the undertails coverts is not typical for Saker (some photos do seem to show some barring though).
- Underwing of Saker usually shows a darker band on the greater underwing coverts, due to dark-centred feathers with white spots on edges. This bird has whiter feathers with narrow dark bars, a pattern I cannot find on photos of Saker.
- Little tail projection beyond wings.
- The taxon of Saker most likely to occur (milvipes) seems to frequently have strong barring to the feathers of the upperparts (scapulars and greater coverts), unlike this bird.

For me the closest fit is with juvenile Barbary Falcon (sometimes treated as a subspecies of Peregrine), as in these photos: ... Bird_Image_ID=49358 ... y_ID=&Location=
- Head pattern with dark mask and moustachial. Moustachial fairly narrow and sharp-tipped. Mask contrasting with paler crown. Pale super behind eye connecting to pale rear crown.
- Eye ring and bill faintly yellow but not distinct (Barbary apparently changes to yellow on bare parts earlier than related species, shortly after fledging).
- Underparts with narrow streaks and distinct arrowheads. It has been suggested to me that the underparts are too white, but I wonder whether that is related to exposure on the photograph; the flight photo suggests some contrast between the white cheeks and sandy breast (giving a hobby-like appearance).
- Upperparts with distinct narrow buff fringes to lesser and median coverts, weak barring on greater coverts.
- Obvious broad barring on tail.
- Underwing greater coverts white with dark bars. The forewing is slightly paler than on the OBI photo, but is this within a range of variation?

As Jonathan has said, more photos would be useful.