ant bird vs ant thrush

ant bird and ant thrush both are nouns.

Word	Noun	Adjective	Verb	Adverb
ant bird	Yes	No	No	No
ant thrush	Yes	No	No	No

As nouns, ant thrush is a hyponym of ant bird; that is, ant thrush is a word with a more specific, narrower meaning than ant bird:

ant bird: any of various dull-colored South American birds that feeding on ants some following army ant swarms
ant thrush: a kind of antbird, with species spanning the genera Formicarius and Chamaeza

Other hyponyms of ant bird include ant shrike, Hylophylax naevioides, spotted antbird.

ant bird (noun)	ant thrush (noun)
any of various dull-colored South American birds that feeding on ants some following army ant swarms	a kind of antbird, with species spanning the genera Formicarius and Chamaeza