bird vs passerine

bird and passerine both are nouns.

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

bird: warm-blooded egg-laying vertebrates characterized by feathers and forelimbs modified as wings
passerine: perching birds mostly small and living near the ground with feet having 4 toes arranged to allow for gripping the perch; most are songbirds; hatchlings are helpless

Other hyponyms of bird include dickey-bird, dickeybird, dicky-bird, dickybird, cock, hen, nester, night bird, bird of passage, protoavis, Archaeopteryx lithographica, archaeopteryx, archeopteryx, Sinornis, Ibero-mesornis, archaeornis, ratite, ratite bird, flightless bird, carinate, carinate bird, flying bird, passeriform bird, nonpasserine bird, raptor, raptorial bird, bird of prey, gallinacean, gallinaceous bird, parrot, cuculiform bird, coraciiform bird, apodiform bird, caprimulgiform bird, piciform bird, trogon, aquatic bird, twitterer.

bird (noun)	passerine (noun)
warm-blooded egg-laying vertebrates characterized by feathers and forelimbs modified as wings	perching birds mostly small and living near the ground with feet having 4 toes arranged to allow for gripping the perch; most are songbirds; hatchlings are helpless
the flesh of a bird or fowl (wild or domestic) used as food
informal terms for a (young) woman
a cry or noise made to express displeasure or contempt
badminton equipment consisting of a ball of cork or rubber with a crown of feathers

bird (adjective)	passerine (adjective)
	relating to or characteristic of the passeriform birds

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