American Birding Association Checklist

Code 1 and Code 2: Regularly occurring North American avifauna.
Includes regular breeding species and visitors. There is no firm designation between Code 1 and Code 2 species, except that logically Code 1 species are more widespread and are usually more numerous. Code 2 species have a restricted North American range, are more widespread, but occur in lower densities, or are quite secretive making their detection often difficult.

Code 3: Rare.
Species that occur in very low numbers, but annually, in the ABA Checklist Area. This includes visitors and rare breeding residents.

Code 4: Casual.
Species not recorded annually in the ABA Checklist Area, but with six or more total records-including three or more in the past 30 years-reflecting some pattern of occurrence.

Code 5: Accidental.
Species that are recorded five or fewer times in the ABA Checklist Area, or fewer than three records in the past 30 years.

Code 6: Cannot be found.
The species is probably or actually extinct or extirpated from the ABA Checklist Area, or all survivors are held in captivity (or releases are not yet naturally re-established).