Of course, we all know better than to use four letter codes for
communications on tweeters. It not the best mechanism for
communicating with the most people, since most people do not
instantaneously recognize coded bird names.

But to answer the questions:

The official AOU spelling is Cedar Waxwing and that's what one
would use to derive the code. BUT both Cedar Waxwing and
Cerulian Warbler would have the same 4-code if the rules you've
posted were applied. So, in cases of conflict different rules
apply and that's where the 3 or 4 different 4-code systems part
company.

Those of us who band birds would call Cedar Waxwing CEDW and
Cerulian Warbler CERW. And we all defer to Pyle (Identification
Guide to North American Birds) for conflicts like MacGillivray's
Warbler (MGWA) and Magnolia Warbler (MAWA), since this is not an
intuitively practical resolution.

All the more reason to use 4-codes sparingly when sharing what
you've seen with others.

--
Mike Patterson
Astoria, OR
celata at pacifier.com

Scale, nature and our infinite capacity to rationalize
http://www.surfbirds.com/blogs/mbalame/archives/003674.html