water ouzel vs oscine bird

water ouzel and oscine bird both are nouns.

Word	Noun	Adjective	Verb	Adverb
water ouzel	Yes	No	No	No
oscine bird	Yes	No	No	No

As nouns, oscine bird is a hypernym of water ouzel; that is, oscine bird is a word with a broader meaning than water ouzel:

water ouzel: small stocky diving bird without webbed feet; frequents fast-flowing streams and feeds along the bottom
oscine bird: passerine bird having specialized vocal apparatus

Other hypernyms of water ouzel include oscine.

water ouzel (noun)	oscine bird (noun)
small stocky diving bird without webbed feet; frequents fast-flowing streams and feeds along the bottom	passerine bird having specialized vocal apparatus