birdnest vs bird nest

birdnest and bird nest both are nouns.

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

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

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

Other synonyms of birdnest include bird's nest.

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

birdnest (verb)	bird nest (verb)
gather birdnests