The following are excerpts from the explanation of band codes used in the AviSys bird data base which I use. I can email the entire band code file as an attachment to anyone who responds to me by email.


The band codes used in AviSys are those established by the
* U.S. Department of the Interior, Fish and Wildlife Service,
* Bird Banding Laboratory.
*
The following is the rationale for the non-standard codes
* that were established because of conflicts created by similar
* bird names:
*
* In the case of code conflict between two normally occurring
* N.A. species, a "three and one rule" has been applied where
* the first three letters of the first word are combined with
* the first letter of the last word. An example of a conflict
* for the code "basp":
*
* "bacs bachman's sparrow"
* "bais baird's sparrow"
*
* However, where the code conflict is between a normally
* occurring N.A. species and a vagrant, the normal code is
* retained for the normally occurring species, and the
* "three and one" rule is applied to the vagrant. Example:
*
* "brsp brewer's sparrow"
* "banp band-rumped storm-petrel"
*
* A small number of code conflicts are not solved by the above
* rules, or create additional code conflicts when the rules are
* applied. For those species, code combinations were selected
* to make the species as recognizable as possible.