Melopsittacus undulatus vs budgerigar

Melopsittacus undulatus and budgerigar both are nouns.

Word	Noun	Adjective	Verb	Adverb
Melopsittacus undulatus	Yes	No	No	No
budgerigar	Yes	No	No	No

As nouns, Melopsittacus undulatus and budgerigar are synonyms defined as:

Melopsittacus undulatus and budgerigar: small Australian parakeet usually light green with black and yellow markings in the wild but bred in many colors

Other synonyms of Melopsittacus undulatus include budgereegah, budgerygah, budgie, grass parakeet, lovebird, shell parakeet.

Melopsittacus undulatus (noun)	budgerigar (noun)
small Australian parakeet usually light green with black and yellow markings in the wild but bred in many colors	small Australian parakeet usually light green with black and yellow markings in the wild but bred in many colors