The Birds is in part a vision of one way the world might end: the planet's other residents could get sick of us and decide to wipe us out. To some extent, this is fanciful; everyone's always predicting the end of the world, and it never happens. On the other talon, our world will, in fact, end at some point. Why not through interspecies warfare? Some critics have suggested that the birds are a stand-in not for the natural world but for a future where machines or nuclear weapons will wipe us out.
MRS. BUNDY: Birds are not aggressive creatures, Miss. They bring beauty into the world. It is mankind, rather, who insists upon making it difficult for life to exist on this planet. If it weren't for birds—
The natural order is being turned upside down. Peaceful birds turn into dive-bombers; birds of a different feather are flocking together. It's what makes the townsfolk distrust Melanie's account, as it goes against everything they know. Mrs. Bundy, the ornithologist, makes the case that you should root for the birds. In this case, the birds are certainly more interesting than the human characters, but we don't think that's what she meant.
TRAVELING SALESMAN: Gulls are scavengers, anyway. Most birds are. Get yourselves guns and wipe them off the face of the earth!
MRS. BUNDY: That would hardly be possible.
DEKE CARTER (DINER OWNER): Why not, Mrs. Bundy?
MRS. BUNDY: Because there are 8,650 species of birds in the world today, Mr. Carter. It is estimated that 5,750,000,000 birds live in the United States alone. The five continents of the world...
TRAVELING SALESMAN: Kill 'em all. Get rid of the messy animals.
MRS. BUNDY: ... probably contain more than 100,000,000,000 birds!
Like the traveling salesman suggests, humans often do try to wipe out animals (or birds) they don't like. The fun (and horror) of The Birds is thinking about what would happen if the birds turned the tables on us. In his bird's-eye view shots, Hitchcock conveys that the birds are in control. While the humans only have their limited visual perspective, the birds can see us all down there and plot their strategy. Those shots are extremely disturbing.
MITCH: I think we're in real trouble. I don't know how or why this started, but I know it's here and we'd be crazy to ignore it ... The bird war, the bird attack, plague—call it what you like. They're amassing out there someplace, and they'll be back. You can count on that. Unless we do something right now, unless we get Bodega Bay on the move, they ... Mrs. Bundy said something about Santa Cruz, about seagulls getting lost in a fog and then flying in towards the lights ... Make our own fog ... we can use smoke pots the way the Army uses 'em.
Mitch plots to fight the birds using science and logic. What's interesting is they never actually put this plan into effect. The full-scale human vs. nature smackdown never happens; the humans just leave. Adding to the inexplicable nature of the attacks is that the birds let them leave without attacking them—a couple of pecks, but that's it.
CATHY: Mitch, can I bring the lovebirds in here?
CATHY: But Mom, they're in a cage.
LYDIA: They're birds, aren't they?
Guilt by association. Lydia draws the battle lines; nature over there, people over here. The lovebirds, caged pets, occupy an intermediate space between people and nature. They stay relatively calm throughout Bird-ageddon, never trying to bust out of their cage or attack anyone. Little Cathy is able to move past the bird phobia to bring the lovebirds with them when they flee. They seem to represent a shred of normal life in the face of all the chaos. Of course, maybe the lovebirds make their move in the fleeing car, and nobody makes it alive to San Francisco. We'll never know.