winter wren vs wren

winter wren and wren both are nouns.

Word	Noun	Adjective	Verb	Adverb
winter wren	Yes	No	No	No
wren	Yes	No	No	No

As nouns, wren is a hypernym of winter wren; that is, wren is a word with a broader meaning than winter wren:

winter wren: small wren of coniferous forests of Northern Hemisphere
wren: any of several small active brown birds of the Northern Hemisphere with short upright tails; they feed on insects

Other hypernyms of winter wren include jenny wren.

winter wren (noun)	wren (noun)
small wren of coniferous forests of Northern Hemisphere	any of several small active brown birds of the Northern Hemisphere with short upright tails; they feed on insects