Real world article
(written from a production point of view)
Referenced in the final draft script of the Star Trek: The Original Series first season episode "Charlie X", a bluejay is a type of Terran bird.
In the scripted stage directions from the aforementioned teleplay, Leonard McCoy was said to be "as irritated as a fussy bluejay," upon arriving on the bridge of the USS Enterprise while Charles Evans was psychokinetically taking command of the USS Enterprise.