rock wren vs jenny wren

rock wren and jenny wren both are nouns.

Word	Noun	Adjective	Verb	Adverb
rock wren	Yes	No	No	No
jenny wren	Yes	No	No	No

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

rock wren: wren inhabiting badlands and mesa country of western United States and Mexico
jenny wren: any of several small active brown birds of the Northern Hemisphere with short upright tails; they feed on insects

Other hypernyms of rock wren include wren.

rock wren (noun)	jenny wren (noun)
wren inhabiting badlands and mesa country of western United States and Mexico	any of several small active brown birds of the Northern Hemisphere with short upright tails; they feed on insects
short-tailed bird resembling a wren