Avibase
Birdnet-Forum
German Association for the Protection of Common Swifts
Clements Checklist
IOC World Bird List
Committee Against Bird Slaugther (CABS)
LBV (Landesbund für Vogelschutz)
NABU (Nature And Biodiversity Conservation Union Germany)
Ornitho
Swiss Ornithological Institute (Vogelwarte Sempach)
Wildvogelhilfe (German or French)
Xeno-canto