bird vs girl

bird and girl both are nouns.

As nouns, girl is a hypernym of bird; that is, girl is a word with a broader meaning than bird:

Other hypernyms of bird include miss, missy, fille, young lady, young woman.

bird (noun)	girl (noun)
warm-blooded egg-laying vertebrates characterized by feathers and forelimbs modified as wings	a young female
the flesh of a bird or fowl (wild or domestic) used as food	a youthful female person
informal terms for a (young) woman	a female human offspring
a cry or noise made to express displeasure or contempt	a girl or young woman with whom a man is romantically involved
badminton equipment consisting of a ball of cork or rubber with a crown of feathers	a friendly informal reference to a grown woman

bird (verb)	girl (verb)
watch and study birds in their natural habitat