Hi Bruce,
I guess most bookstores in HK do not have a wide stock of bird books as the local market is not too big and I usually order books via internet.
Nevertheless, you may try these two ones
1. Swindon (see "about us" for the address of branches)
http://www.swindonbooks.com/
2. Commercial Press
http://www.hkcp.com/ww/english/retailing.htm
The ones at Star House near Star Ferry Pier (Kowloon side, Tsim Sha Tsui) and Causeway Bay should have more English books.
Some fieldguides and books about wildlife and countryside in HK are bilingual (Chi and Eng) but are placed in the Chinese section, so better to check with the storekeeper.
Good luck,
Captain Wong
