This big bird is the greater coucal or crow pheasant (Centropus sinensis). But it is actually a cuckoo, and don't try eating one, as they taste disgusting
How do I know this (given that all birds in HK are protected by law? Well, I have read that they were mistaken by English soldiers in India for pheasants, and they reported it "evil flavoured" giving it the nickname of "Griff's pheasant". A lot of animals taste of what they eat, so this bad taste is probably because they are known to eat toxic fruits.
Yes, its a cuckoo, but they are non parasitic, ie they do not lay their eggs in other's nests. They are quite unmistakable in Hong Kong, as not many birds are this big, and they have a long tail and coppery brown wings. But they are weak fliers, and are often seen clambering about in vegetation or walking on the ground as they forage for insects, eggs and nestlings of other birds, caterpillars and small vertebrates such snakes and lizards, but they also eat seeds and fruit.
The flesh was once eaten in India as a folk cure for tuberculosis and pulmonary ailments.
here below a juvenile coucal that I had previously mistaken for a Koel.
Please also see www.wildcreatureshongkong.info for ID and animal information, around species are listed with photo ID, and www.hongkongsnakeid.com for snakes.