bird nest vs birdnest

bird nest and birdnest both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird nest	Yes	No	No	No
birdnest	Yes	No	Yes	No

As nouns, bird nest and birdnest are synonyms defined as:

bird nest and birdnest: nest where birds lay their eggs and hatch their young

Other synonyms of bird nest include bird's nest.

bird nest (noun)	birdnest (noun)
nest where birds lay their eggs and hatch their young	nest where birds lay their eggs and hatch their young

bird nest (verb)	birdnest (verb)
	gather birdnests