Hitchcock called it "God's point of view." It's an aerial shot of Bodega Bay. A soft wind mutes all sounds and everything in the frame is peaceful except for a small strip you could cover up with your thumb. In that tiny strip, everything important in the world changes. "The Birds" is filled with scenes like these. There's conflict in the air, but there's also just a soft wind and the compressed white noise of the sea nearby.
Up until the last 45 minutes of the movie, when the landscape becomes choked with birds, there's a similar disconnection in the lives of the characters, between the moments of mayhem and the ordinary flow of their lives. The focus of the first part of the movie is on the quirky romance between Melanie and Mitch and of the negotiation of egos and needs between Melanie and Mitch's mom Lydia. A full 25 minutes passes before the first bird attack takes place. We see yet another and the aftermath of a third and even then, the dialogue between the principle characters is about their relationships and their feelings. It isn't until 1:15 into the film that birds become the central part of the dialogue.
This happens in a scene in a coffee shop. The schoolyard attack has just happened and Melanie is on the phone to her news tycoon dad. Two men sit at the bar eavesdropping on the phone call. The waitress and the cook call out orders. A mariner talks about his own bird problems. A drunk at the end of the bar calls it the end of the world. A woman sits anxiously with her two children, trying to get everyone to stop talking about such scary things. The birds are a hot topic, but that's about it. Everyone's still nestled in the belief that this day, like all other days are about ordinary concerns.
All that stops when the first explosion happens. Now nothing else matters. The birds are everything.
At the outset, the birds are at worst a nuisance. The greatest threat is that the birds might provide enough of a distraction while we're operating a car or a gas pump that we lose control of our devices and that's what actually kills us. Not the bird attack, but the explosion or the crash. (Of course, it's also worth pointing out that the first fatality is an old man whose eyes have been plucked out, but c'mon: dude was old. Old people are dumb. That's why they don't live long.)
But the birds increase in number until all the landscape from here to the horizon is covered with them. Any startling noise and you won't have 5 or 10 to try to wave away from your eyeballs, but rather thousands.
You could draw a limited comparison to a slow-zombie movie. The threat can be avoided so long as it comes to us in small numbers. Higher numbers though, we're fucked. Also, like a zombie movie, the action eventually must gravitate towards a small confined space. There's nothing left but indoors; the birds own everything else.