Plot hole: When Jessica Tandy walks into Mr. Faucet's house everything is in perfect shape except a couple of broken cups, and there's not a dead bird in sight. (00:59:40)
The Birds (1963)
1 plot hole - chronological order
Directed by: Alfred Hitchcock
Starring: Jessica Tandy, Rod Taylor, Suzanne Pleshette, Tippi Hedren
Continuity mistake: A blond boy in a light brown shirt is attacked by a crow and goes from having no blood on his neck to having a lot of blood smeared on his neck between shots. (01:14:10)
Melanie Daniels: They're coming! They're coming.
Trivia: Although it lasts for only several minutes on screen, the scene where Tippi Hendren is attacked by the birds in the bedroom took seven days to film.
Question: What's making the birds go insane and attack people?
Answer: None of the characters knew why the birds attacked, or the reason it was confined to the one town of Bodega Bay. The incident was so isolated that the outside news media was barely aware it was occurring or knew its severity, so there was no investigation into it at the time. Alfred Hitchc0ck's explanation was that the birds were rising up against humans to punish them for taking nature for granted.
Answer: It is never explained, probably because it would ruin the mystery of the film to spell it out.
If you are a Hitchcock fan, you pay attention to dialogue. They mention quite often that it started Melanie's arrival, of which she brought 2 caged birds. The rest is implied.