The Birds (Greek: Ὄρνιθες) is a comedy by Aristophanes first produced at the Athenian City Dionysia in 414 BC. It's fantastic plot may reflect an appetite for escapism during the tense period in which the city awaited the outcome of the Sicilian expedition. The play's protagonists are two Athenians who abandon the city go and live among the birds, who they persuade to build a city in the air, Nephelokokkygia or Cloudcuckooland, from which they force gods and humans to come to terms with them.
Free online texts
Internet Archive: L 488 - Aristophanes II - Peace, Birds, Frogs. Bilingual Greek-English Loeb edition. Multiple formats.
Poetry in Translation: Birds, translated by George Theodoridis. Multiple formats.
University of Adelaide (Internet Archive): The Birds. English translation, multiple formats.
BBC Radio 4 In Our Time: Comedy in Ancient Greek Theatre. Melvyn Bragg with Paul Cartledge, Edith Hall and Nick Lowe.
History of Ancient Greece: o54- Old Comedy and Aristophanes. Podcast by Ryan Stitt.
Wikipedia: The Birds (Play)
The Great Conversation: Further reading at Tom's Learning Notes
Ancient Greek resources: Learn to read Greek classics in the original.
Bloom's Western Canon: The Birds is listed.