bird vs birdwatch

bird is a noun but birdwatch is not a noun.

As verbs, bird and birdwatch are synonyms defined as:

bird (noun)	birdwatch (noun)
warm-blooded egg-laying vertebrates characterized by feathers and forelimbs modified as wings
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 (verb)	birdwatch (verb)
watch and study birds in their natural habitat	watch and study birds in their natural habitat