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Caspian Tern was created in 1770.
Sterna caspia
This is a Tern. Three match your description but since you talk of a black plume, it is the Elegant Tern. Two others are similar- Royal and one other.
We need location, size and behavior to be sure, but it is probably some sort of tern, possibly a Royal or Caspian.
The tern's cousin