4-letter Alphabetic (“alpha”) codes are abbreviations of English or scientific bird names that were created by the Bird Banding Laboratory (BBL) for use by bird banders in submitting data in shorthand. They allow quicker data entry than filling out the full English or scientific name of a species and they can also serve to cross-check other recorded names or numeric data.
The basic codes were derived from a simple set of rules for reducing a name to four letters. A major problem is that the rules can create “collisions”; cases where two (or more) different names reduce to the same four letters. In these cases, different codes had to be created ad hoc. Unfortunately, if you want to use the codes, you simply must memorize the special cases; there is no way around it.