In Alfred Hitchcock's The Birds, a flock of various birds is driven to attack a coastal community for seemingly no reason. The film's horror rests in making the seemingly mundane birds, not any supernatural creature, the monster lying in wait to attack humanity. The film draws inspiration from a short story by Daphne du Maurier with the same name that was published in 1952. However, another real-world event closer to the film's release might have inspired Hitchcock to make the film and may reveal the true cause of the birds' attacks.

The Real-World Incident That Inspired The Birds

In The Birds, released in 1963, Melanie Daniels meets Mitch Brenner in a pet store before she travels to his hometown, Bodega Bay, to deliver a pair of lovebirds for his sister Cathy's birthday. What begins as a meet-cute shifts into a psychological drama as the birds begin attacking, seemingly without cause, and turn the film into a survival horror movie. Melanie and the Brenner family struggle to evade the birds' attacks in the Brenner home. The film ends with Melanie and the Brenners escaping Bodega Bay in her car as the birds watch ominously. The birds seem to have ended their reign of terror, but without a known cause, it is uncertain whether the birds will begin to attack again later.

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While the birds' motivations are never explained in the film, there is a biological reason for the bird attacks. In an article for ABC News, Alexandra Ludka explains that a similar incident to The Birds actually occurred around Monterey Bay, California in 1961. She writes that "hoards of disoriented seabirds rammed themselves into the sides of homes," but the explanation for why was not found until decades later after the incident and the release of Hitchcock's film.

Ludka explains that, after other incidents involving toxic mussels and animal stranding, researchers found that certain algae emit toxins that cause "amnesia, disorientation and seizures" in creatures that ingest the toxins. Thus, researchers now believe that the Monterey Bay incident was caused by a flock of birds that had ingested the algae and suffered the effects of the toxin.

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Daphne Du Maurier's Influence On The Birds

Hitchcock's The Birds also was inspired by a short story of the same name by Daphne du Maurier, first published in 1951, which takes place in Cornwall's countryside in a farming community. The story focuses on Nat Hocken, a farmer, and his family as they desperately try to protect their home as thousands of birds descend upon them. Unlike the film, which limits the attacks to Bodega Bay and the surrounding area, in the short story, the bird attacks are not limited to Cornwall. The birds besiege all of England, and the story quickly takes an apocalyptic turn. Unlike the movie, where the bird attacks end, there is no end in sight for the Hocken family's horror. While Nat and his family are alive at the end, it is unclear whether they will be able to stand against the birds forever.

While this short story was published ten years before the Monterey Bay incident, it still could have been inspired by similar events. In Ludka's article, she states that the toxic mussels were ingested in Prince Edward Island, an eastern Canadian island. This fact shows that the algae that release this toxin exist all over the world, not just in the Pacific Ocean. In an article for dumaurier.org, Ann Willmore writes that Daphne du Maurier was inspired to write "The Birds" after witnessing "gulls wheeling to attack the farmer" who lived next door to her. While the birds did not actually attack the farmer, they still could have been under the influence of a similar toxin. However, there is no conclusive evidence tying these particular birds' behavior to the toxin or the bird's behavior in Monterey Bay.

In an article for The Guardian, Patrick McGrath explains that du Maurier was not a fan of Hitchcock's adaptation due to the changes he made. McGrath writes that du Maurier "was baffled as to why the great director had distorted it as he had." The change in setting at least can probably be partially attributed to the Monterey Bay bird bombardment prior to the film's release. The Birds leaves the bird's motivations unknown because the reason for the real-world birds' actions is still a mystery, but at least audiences know that algae and poison, not true malice, motivated the avian attacks.