At a San Francisco pet store, socialite Melanie Daniels meets lawyer Mitch Brenner, who wants to buy lovebirds for his sister Cathy's 11th birthday. Recognizing Melanie from her court appearance regarding a practical joke gone awry, Mitch pretends to mistake her for a shop employee. Mitch tests Melanie's knowledge of birds, which she fails. He discloses his prior knowledge of her and leaves without buying anything. Smitten, Melanie buys the lovebirds and drives to Bodega Bay after learning Mitch has gone to his family's farm for the weekend. Melanie is directed to a teacher at Bodega, Annie Hayworth, to learn Cathy's name. Annie is Mitch’s ex-lover, but their relationship ended due to his overbearing mother, Lydia, who dislikes any woman in Mitch's life.
Melanie rents a boat and crosses the bay to discreetly leave the lovebirds at the Brenner farm. Mitch spots Melanie as she leaves and drives to meet her at the dock. As Melanie approaches the wharf, a gull attacks her. Mitch tends to her head wound inside a diner. Lydia arrives and meets Melanie, whom Mitch invites to dinner. At the farm, Lydia's hens are refusing to eat. Lydia dislikes Melanie due to her exaggerated reputation, as reported in gossip columns. Mitch invites Melanie, who is staying with Annie, to Cathy's birthday party being held the next day. Later, there is a thud at Annie's front door. A dead gull is found at the threshold.
At Cathy's party, Melanie tells Mitch about her troubled past and her mother running off with another man when she was Cathy's age. During a game, the children are attacked by gulls. Later that evening, as Melanie dines with the Brenners, sparrows swarm the house through the chimney. Mitch insists she delay driving back to San Francisco and stay the night. The next morning, Lydia visits her neighbor to discuss why their chickens will not eat. She discovers broken windows in his bedroom and his eyeless corpse, pecked by birds, and flees in horror. While recovering at home, Lydia fears for Cathy's safety, and Melanie offers to pick her up at school. As Melanie waits outside the schoolhouse, a flock of crows engulfs the jungle gym behind her. Anticipating an attack, she warns Annie. Rather than leaving the students in the building with its large windows, they evacuate them, and the crows attack. Mitch finds Melanie at the diner. When gulls attack a gas station attendant, Mitch and other men assist him outside. The spilled gasoline is ignited by an unaware bystander's match, causing an explosion. During the escalating fire, Melanie and others rush out, but more gulls attack. Melanie takes refuge in a telephone booth. Mitch saves her, and they return to the diner. A distraught woman blames Melanie for the attacks, claiming (from what others told her) they began with her arrival. Mrs. Bundy, an ornithologist who scoffed at the reports of birds attacking, sits in stunned silence.
Mitch and Melanie go to Annie's house to fetch Cathy. They find Annie's body outside; she was killed by the crows while protecting Cathy. They take a traumatized Cathy home. That night, Melanie and the Brenners barricade themselves in the family home, which is attacked by birds that nearly breach the boarded-up doors and windows. During a lull, Melanie investigates a fluttering sound in the attic bedroom. After discovering that the birds have pecked their way in through the roof, Melanie is attacked, trapping her until Mitch pulls her out. Mitch insists they all drive to San Francisco to take Melanie, now injured, traumatized and catatonic, to a hospital. As Mitch readies Melanie's car for their escape, a sea of birds has gathered around the Brenner house. Mitch quietly moves the car out. The car radio reports bird attacks on nearby communities such as Santa Rosa, and that the military may intervene. Cathy retrieves her lovebirds (the only birds who do not attack) from the house and joins Mitch and Lydia as they escort Melanie past a mass of birds and into the car. The car slowly drives away as the birds watch.
