birdwatch vs bird

birdwatch is not a noun while bird is a noun.

Word	Noun	Adjective	Verb	Adverb
birdwatch	No	No	Yes	No
bird	Yes	No	Yes	No

As verbs, birdwatch and bird are synonyms defined as:

birdwatch (noun)	bird (noun)
	warm-blooded egg-laying vertebrates characterized by feathers and forelimbs modified as wings
	badminton equipment consisting of a ball of cork or rubber with a crown of feathers
	a cry or noise made to express displeasure or contempt
	the flesh of a bird or fowl (wild or domestic) used as food
	informal terms for a (young) woman

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