Universal Pictures knew horror.
They were the home of the Dracula, The Mummy, The Invisible Man, and Frankenstein franchises, and from the 1920s through the 1950s, their bread-and-butter productions were low-budget horror flicks. (Source)
Hiring Alfred Hitchcock? Yeah, that definitely upped their game.
Universal had a long on-again, off-again, sometimes contentious relationship with Hitchcock. Way back in 1942, Hitchcock made a film called Saboteur for Universal, in which the studio made him use contract performers Robert Cummings and Priscilla Lane. Did anyone tell Picasso what color to use in his paintings? Did they tell Shakespeare what words to put in his sonnets? Nah, but Hitchcock wanted to get paid, so he took Cummings and Lane and slapped them down in his film like he was told.
He wasn't happy about it.
By the 1960s, Hitchcock was a world-famous director. In 1960, he made what was probably his most successful film for Universal. The horror/suspense movie Psycho was a massive box-office hit; it made Hitchcock himself more than $15 million dollars. He used the money to buy into MCA, Universal's parent company, in the hope that they'd have to stop messing with him. He agreed to make six more films for Universal.
Did it work? Not really. Universal did give Hitchcock a lot of time and resources to make his next film, The Birds, but the studio couldn't help meddling. Hitch's original conclusion shows Mitch's car driving through all the birds, followed by a fade out.
Ambiguous, creepy, and unsettling, right?
Well, Universal thought it was a little too creepy and unsettling and confusing. So, instead of a fade out, they put in a title card saying, "The End." Hitch had wanted audiences to feel like the story did not end and would not end—that maybe the bird attacks would continue.
That would keep everyone awake nights, yeah?
P.S. Sound familiar? Some streaming and DVD versions have eliminated the end title in keeping with the director's wishes.