Another merchant worth checking for bird and other subject books is
Alibris.com, from which MANY used and some NEW books may be found,
many out of print but still available. I've used them for several
purchases, and happy I did! [NOTE: I do not have any financial stake
in their income or survival] Their main page has changed since I
first used it, but one must still type in subject, or title, or
author, to go to sometimes extensive list of books they either have
or can readily locate, from trusted sources (third-party sellers)
often at good prices, sometimes better than "new" in today's market -
Jim Greaves