AFAIK there is at least one that I saw twice on the large tree at Ma Hang Chung Road little park, in which one time she attempted (I think it succeeded) to catch little bird (a Tree Sparrow). I wonder whether she is the member of the flock you described, as I saw her flew away towards Kowloon City.
BTW there is another (I think it is another individual) appeared around To Kwa Wan Market and the hills behind Lok Man Sun Chuen.
Cheer
Gary