1. Tippi has a weird effect on birds wherever she goes, and the power is magnified when strong emotional feelings are involved.
2. The birds have become 'aware' and are nuts.
3. Jessica Tandy's character was uses telepathic powers to control the birds and keep Tippi from interfering with her happy home life.
4. Hitchcock wanted to use the birds as a substitute for Communist expansion and contrast the different attitudes people had towards it.
The Birds has a progression and flow to it. Things start small and slowly build with every scene. Hitchcock was great at building suspense and making the normally innocent menacing. Shower muder scenes, attempted murder in a cornfield, little birds pecking at your face... these are all everyday things that Hitchcock used to make people scared. This is a super gynocentric film. There is a battle over Mitch, who is still unmarried for some reason, between Tippi, Anne and his mom. It is a bit weird that the birds seriously attack both Anne and Tippi, but Jessica Tandy stays unmarked. The Birds is freaky. I love its mood, and think it is the type of movie modern film directors wish they could make.
Why? Look at every M. Night Shyamalan movie. It's some huge event that is happening that never gets answered or resolved and the main characters are not the cause of action. They just exist in the situation. That is the Birds in a nutshell. It's like M. Night saw the Birds and wanted to make his films all similar to it because it rocked. M. Night fails for many reasons but one big one is: no one cares about his core characters. No one liked Bruce Willis' family in Unbreakable, the only likeable character in Signs was the cute little girl, and The Village was devoid of charisma or even a good villain. The r-tards in Hollywood are going to remake the Birds and Tippi isn't happy.
Does Tippi Hedren make the film? No, but she is enjoyable. She stalks a man, and it does not affect how viewers feel about her. She tracks some guy she meets quickly, and people swallow it whole. Her antics are strange, she takes risks and really shoves herself into this man's life with no reason besides being a rich girl interested in a single guy. She plays the assertive woman, playful charmer, and aggressive flirt well. There is plenty of mischeif in her smile and sly glances. Later she would star in Marnie for Hitchcock, and be better than she was in the Birds. Tippi was one of Hitchcock's many blonde leading ladies, and and stand out amongst the many.
The Birds has a dark tone to it. The attack scenes and aftermath shots are pretty graphic for the 1960s. The bird attack on Tippi in the house is just as bad as the shower scene with Janet Leigh in Psycho. I would argue it is worse as the birds are living, breathing animals. The question 'why are the birds doing this?' is never answered, and that mystery is far better left unsolved for viewers to dicuss for years than for a director's commentary to answer on a dvd. Sometimes the advance of technology can be a bad thing, and I am thankful that Mr. Hitchcock never lived long enough to record commentaries for his movies.