Cassin's kingbird vs kingbird

Cassin's kingbird and kingbird both are nouns.

Word	Noun	Adjective	Verb	Adverb
Cassin's kingbird	Yes	No	No	No
kingbird	Yes	No	No	No

As nouns, kingbird is a hypernym of Cassin's kingbird; that is, kingbird is a word with a broader meaning than Cassin's kingbird:

Cassin's kingbird: a kingbird seen in the southwestern United States; largely grey with a yellow abdomen
kingbird: large American flycatcher

Other hypernyms of Cassin's kingbird include Tyrannus tyrannus.

Cassin's kingbird (noun)	kingbird (noun)
a kingbird seen in the southwestern United States; largely grey with a yellow abdomen	large American flycatcher