The American Ornithologists’ Union (AOU) has released the 51st supplement to the AOU Checklist. Expert birder Michael Retter has an excellent summary of these changes. Bird sound expert Nathan Pieplow has additional info as well, including sounds.
These periodic changes occur when new scientific information is learned about species and their relationships to each other. For “listers” these changes involve refiguring their lifelists and often adding new species.
It is always a good idea to study notable subspecies of birds that are likely or possible to be “split”.