boat-billed heron vs heron

boat-billed heron and heron both are nouns.

Word	Noun	Adjective	Verb	Adverb
boat-billed heron	Yes	No	No	No
heron	Yes	No	No	No

As nouns, heron is a hypernym of boat-billed heron; that is, heron is a word with a broader meaning than boat-billed heron:

boat-billed heron: tropical American heron related to night herons
heron: grey or white wading bird with long neck and long legs and (usually) long bill

boat-billed heron (noun)	heron (noun)
tropical American heron related to night herons	grey or white wading bird with long neck and long legs and (usually) long bill