sedge bird vs Old World warbler

sedge bird and Old World warbler both are nouns.

Word	Noun	Adjective	Verb	Adverb
sedge bird	Yes	No	No	No
Old World warbler	Yes	No	No	No

As nouns, Old World warbler is a hypernym of sedge bird; that is, Old World 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
Old World warbler: small active brownish or greyish Old World birds

Other hypernyms of sedge bird include true warbler.

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