sedge bird vs true warbler

sedge bird and true warbler both are nouns.

Word	Noun	Adjective	Verb	Adverb
sedge bird	Yes	No	No	No
true warbler	Yes	No	No	No

As nouns, true warbler is a hypernym of sedge bird; that is, true warbler is a word with a broader meaning than sedge bird:

sedge bird: small European warbler that breeds among reeds and wedges and winters in Africa
true warbler: small active brownish or greyish Old World birds

Other hypernyms of sedge bird include Old World warbler.

sedge bird (noun)	true warbler (noun)
small European warbler that breeds among reeds and wedges and winters in Africa	small active brownish or greyish Old World birds