Four-digit Codes (German: Vierstelliger Code) is a concept based on the real life American Ornithological Society's "Alpha" codes. (For example, Bald Eagle is BAEA). A similar concept is Six-digit Codes for scientific names.
No two codes must be the same, or it gets confusing. No codes should have inappropriate language either.
- Bluegill and Bluethroat: Bluethroat's code conflicted with Bluegill's. It has been changed to BLUG.
- Jaguar and Jaguarundi: Since Jaguar comes first in the Anidex, it gets the code JAGU, while Jaguarundi gets the code JAGA.