The Birds is basically a movie about foreshadowing. From the beginning the increasing presence of the birds is emphasized. On the boat she first notices the birds, and she receives an injury from one of the birds. This scene is heavily contrasted with the concluding scene in which she is brutally attacked by a swarm of birds.
The birds tend to appear in settings where characters are isolated and vulnerable. This creates a sense of paranoia that Hitchcock is famous for in all of his films. The eerie violin music and occasional squawk of the birds drive this suspenseful mood.
Once scene that is a good example of this foreshadwing is when a character gets out of their truck and walks into the house and walks in and notices the cups broken and the evidence builds and builds until the conclusion of finding the body.