Did the lovebirds cause it?

no

I know this is an old post but that was my theory too. Overall though I was not impressed with the movie, long and boring.

"I knew it. I'm surrounded by *beep*

The story is How would you deal with an uncontrollable force? In this case nature.
It doesn't matter what caused it, it is about how would You react in a situation you can't control.
And Hitchcock was able to put YOU in that phone booth, or walking down that hall, Didn't he?

Ephemeron.

I wondered the same thing!

This is my take on the love birds.

To me this film is about peace and reconciliation, both on the personal and societal level. Remember also Hitchcock's strong Catholic beliefs, which he sometimes referenced in his films in subtle ways. Looking at the film from a religious/philosophical level the final shot makes a lot of sense. In the distance we see a ray of light breaking through the clouds. Mitch's mother and Melanie have a moment of tenderness together. The love birds represent the Christian idea of reconciliation and peace in the face of a frightening world we cannot explain or control. The apocalyptic tone of the story is driven home in the diner scene and the "It's the end of the world" refrain by one of the customers. Mrs. Bundy is like a rationalist who tries to explain things in scientific terms, although the film itself gives us no reason why the birds attack and Mrs. Bundy appears shocked and surprised by the events herself.

Keep in mind this film was made right after the Cuban Missile Crisis. Indeed, Hitchcock even went on to make a film dealing directly with that event in Topaz, so it's not far-fetched at all to make this connection. It's as if the characters in the story have reconciled with each other and are being given a second chance, just as the world had been given a second chance after the missile crisis. Even if nuclear war wasn't the intended subtext of the film, in a general sense the attacking birds are a symbol of chaos while the love birds are a symbol of reconciliation and hope.