Actually very rarely heard on HK Island, or at least they were in the past, when I lived there.
I heard one once in ten years from '87 - '97.
Rather localised in Sai Kung, where I live now, but we do have them roving around here in the spring at least, where I live now at Tsiu Hang Special Area.
Nam Shan near Sai Kung town, and Ho Chung are also strongholds.