sedge wren vs Old World warbler

sedge wren and Old World warbler both are nouns.

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

As nouns, Old World warbler is a hypernym of sedge wren; that is, Old World warbler is a word with a broader meaning than sedge wren:

sedge wren: 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 wren include true warbler.

sedge wren (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
small American wren inhabiting wet sedgy meadows