young bird vs biddy

young bird and biddy both are nouns.

Word	Noun	Adjective	Verb	Adverb
young bird	Yes	No	No	No
biddy	Yes	No	No	No

As nouns, biddy is a hyponym of young bird; that is, biddy is a word with a more specific, narrower meaning than young bird:

Other hyponyms of young bird include fledgeling, fledgling, baby bird, nestling, eaglet, chick, cygnet.

young bird (noun)	biddy (noun)
a bird that is still young	young bird especially of domestic fowl
	adult female chicken