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Alfred Hitchcock may not have been a marine biologist, but he was a keen observer of the news. So it was that the famed horror movie director may have found inspiration for the 1963 film, "The Birds," from a mass bird casualty that occurred near his home on August 18, 1961. That morning, the residents of Capitola, California, awoke to the sight of hundreds of dead sooty shearwaters strewn across the streets and the sound of others ramming themselves into their roofs.
A mystery at the time it happened, scientists now believe the cause for this bizarre display of behavior was domoic acid, a deadly toxin released by algae exposed to urea pollution, reports Nature's Amy Coombs. The discovery was made by Raphael Kudela, an oceanographer from the University of California, Santa Cruz, who was studying Pseudo-nitzschia australis, a common species of algae.
Image from Brian Bill/NOAA
A deadly neurotoxin
The blooms the species produces, though typically harmless, can sometimes result in the release of domoic acid, a toxin that causes extensive brain damage and provokes unusual behavior patterns that resemble homicidal tendencies -- hence the large number of birds slamming into the residents' rooftops. The acid does this by tightly binding to surface receptors on excitatory neutrons, which prevents cells from turning off. Over the last few decades, domoic acid has been responsible for several large outbreaks of deaths and illness, as Coombs notes:
Although researchers can only speculate that domoic acid caused this historic event, modern toxicologists have conclusively linked the toxin to more recent cases. In 1987 contaminated shellfish poisoned 100 people on Prince Edward Island in Canada, killing three and causing many cases of amnesia. In 1998, 400 disoriented sea lions died along California's central coast — domoic acid was traced back to contaminated fish that swam through a toxic bloom before being eaten by the sea lions. "Every few years there is a big outbreak that causes otters, pelicans or sea-lion deaths," says Kudela.
Urea responsible for stimulating the release of domoic acid
Scientists have long thought that human pollution played a key role in stimulating the deadly blooms but did not know which particular pollutant caused P. australis to produce the toxin. Kundela and his colleagues tested a number of chemicals found in fertilizer, such as nitrate and ammonium, to find out; it turned out that urea was the only chemical that boosted production of domoic acid -- in some cases even doubling it. Indeed, they found concentrations of the acid to be high enough in Monterey Bay and San Francisco Bay to account for recent bloom events.
Hitchcock used coverage of the event as "research material" for The Birds
Even though there is no way to verify whether the bloom events, and the large amounts of domoic acid they produced (resulting in the shearwaters' strange behavior), did serve as inspiration for Hitchcock's film, "The Birds," Kudela says that significant quantities of urea were leaching into the ocean at the time due to the prevalence of unregulated septic tanks. Furthermore, a local paper at the time reported that Hitchcock asked for news of the event to use as "research material for his latest thriller," which became "The Birds."