The scene when Norman Bates stabs Marion in the shower has a few references to birds in it. The sound effects during the actual stabbing are high pitched shrieks similar to those of a bird of prey such as a hawk. The weapon and stabbing technique used to kill Marion Crane work together to form an allusion to birds. He uses a knife that he stabs downward with. This act is similar to how a bird would attack its prey. Marion is lower to the ground than Norman which adds to the idea that Hitchcock is using Norman to represent a bird swooping down on its prey.
Hitchcock’s use of actual birds in some shots adds to the menacing nature of the movie. The scene with a large stuffed bird surrounded by shadows serves as foreshadowing for the trouble that is looming ahead for Marion.
Wilshire, Peter. Alfred Hitchcock's PSYCHO and 'The Art of Pure Cinema. Australian Screen Education. 2009
This is an article written about Alfred Hitchcock’s film Psycho. It talks about how Psycho was one of Hitchcock’s experimental films because it was so unlike the norm of the day. It discusses how he assembled certain elements of film to create a frightening experience for his audience.
Chandler, Charlotte. It's Only a Movie: Alfred Hitchcock; A Personal Biography. Applause Books.
This source is a full book length biography of Alfred Hitchcock. I will use sources like this to search for reasons as to why Hitchcock was so interested in