Simple solution: tennis rackets
I could kill/cripple hundreds of attacking birds with a tennis racket in just a few minutes. Each swing would put a couple/few birds out of commission if they were swarming close together like in the movie.
It's ridiculous that no one thought to arm himself with a tennis racket. Someone mentioned guns, but they wouldn't be very effective against swarming/attacking birds. If they'd had tennis rackets, the biggest problem would have been the fun of sending asshole birds sailing a couple hundred feet with every swing, being over too quickly.
About 21 years ago a bat got into my house and my very first thought was to get my tennis racket, not my gun. I found where it had landed in the kitchen and I stood there about 10 feet away waiting for it to make its move. It decided to fly directly at my face, and I treated it like a volley at net. It was dead before it hit the floor.