bird nest vs bird's nest

bird nest and bird's nest both are nouns.

Word	Noun	Adjective	Verb	Adverb
bird nest	Yes	No	No	No
bird's nest	Yes	No	No	No

As nouns, bird nest and bird's nest are synonyms defined as:

bird nest and bird's nest: nest where birds lay their eggs and hatch their young

Other synonyms of bird nest include birdnest.

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