AN AVIAN HOSPITAL WAS BUILT ON THE SET.
Through a meticulous positive reinforcement process, animal handler Ray Berwick trained hundreds of live birds for use in Hitchcock’s movie. Most of these were wild-caught crows, ravens, seagulls, and sparrows. Berwick oversaw an entire bird-wrangling team whose members spent a huge amount of time corralling their feathered co-workers between takes. To ensure that none of the animals was harmed, the American Society For the Prevention of Cruelty to Animals (ASPCA) assumed an active role in the production. Under their watchful eye, the crew set up a makeshift avian hospital.
“We actually built an aviary onto the set for birds that had been hurt or injured,” Veronica Cartwright, who played Cathy in the film, said. Another measure taken in the name of animal welfare was the construction of a large net, which the special effects team draped over the living room set; this kept the birds from flying haphazardly through the rest of the studio.
The wrangling team had plenty of other tricks up their sleeves as well. Sometimes, to get their feathered friends to fly toward a camera, the crew would suspend a hunk of meat beneath the lens. In one interview, Hitchcock noted that a lot of prep work went into the shot in which a seagull latches onto a girl at a birthday party, harassing her as she tries to run off. “[We] built a little platform on her shoulder and a gull was put there,” Hitchcock explained. For safety reasons, its beak was bound shut with wire.
From the article found here: http://mentalfloss.com/article/518114/10-fascinating-facts-about-birds.