In August 1961, thousands of crazed seabirds flew over the shores of Monterey Bay, California. The strange event inspired Alfred Hitchcock, who spent the summer in the area, to devise the script for his famous film Birds (1963), in which flocks of frenzied birds attack the residents of a small coastal town, Bodega Bay.
Today we know that those birds had incorporated into their metabolism a neurotoxin produced by the bloom of marine algae, diatoms.
These days, 70 years later, tons of dead fish are surfacing in the San Francisco Bay. The high temperatures and the increase in the water of nitrates, fertilizers and other types of waste from urban and industrial areas have once again formed a perfect breeding ground for the bloom of a microscopic algae that affects dozens of marine species that They are the food of the birds. This recent event is closely related to the event that inspired Alfred Hitchcock.
The damage of red tides
Eutrophication, the excess supply of inorganic nutrients, produces blooms, that is, exponential multiplications followed by massive accumulations of phytoplanktonic organisms, among others of certain algae that give the water the characteristic color of red tides. Among other harmful effects, today we know that these algae release neurotoxins that can alter the behavior of aquatic birds.
Probably the earliest record of the toxic effects of algal blooms appears in the Old Testament when the waters of Egypt turned to “blood.” But much earlier, seventy million years ago, hundreds of dinosaurs failed to escape what turned out to be a death trap caused by toxic algal blooms in the water that had lured them in to quench their thirst.
The neurotoxins that reach the birds
Red tides are associated with the production of neurotoxins such as domoic and kainic acids. These neurotoxins are incorporated into the food chain and accumulate in bivalve molluscs or in fish such as anchovies and sardines that are the food of marine birds. Ingesting them alters their neuronal functioning.
Domoic and kainic, two chemical analogs of glutamic acid, are highly toxic for vertebrate metabolism. When they pass through the blood-brain barrier of birds and mammals and bind to neuronal glutamic receptors, they cause symptoms that were first detected in 1987 in Canada and twenty years later in Spain.
The red tide that inspired Birds
On August 18, 1961, a California newspaper, the Santa Cruz Sentinel, reported that thousands of crazed seabirds swept the shores of Monterey Bay. The birds, which regurgitated anchovies, were gray shearwaters (Ardenna grisea). In 1991 a similar episode occurred in the same area. This time it affected brown pelicans (pelicanus occidentalis) who collapsed on the ground disoriented and dying.
The first record of domoic acid
Although diatoms of the genus Pseudo-nitzschia have lived in California waters for millennia, domoic acid was only detected in 1991 when high concentrations of these diatoms and the domoic acid they produce were found in the digestive tracts of Monterey Bay fish. By eating these contaminated fish, the pelicans had incorporated into their metabolism the neurotoxin produced by the diatom bloom.
Before this finding, seabird mortality episodes off the California coast were attributed to other factors such as fog, infectious diseases, oil spills and abusive fishing practices.
One such episode was the accumulation of disoriented gray shearwaters in Monterey in the summer of 1961, an event that probably inspired Hitchcock to devise the screenplay for Birds, adapted from a short story by Daphne du Maurier, an extraordinary suspense story and apocalyptic message in which, in a romantic context, some birds begin to show violence against humans.
For several weeks in the summer, huge flocks of shearwaters feed on krill, squid and fish in the productive waters of California bays like Monterey affected by the California Current. In the summer of 1961, the shearwaters covered the skies of the bay, flying clumsily at random, landing anywhere to regurgitate anchovies before dying in the streets in death rattles.
The study that confirmed the link between diatoms and shearwaters
That Pseudo-nitzschia was responsible for the poisoning of birds in 1961 was a plausible hypothesis. The verification of it came with a research work focused on demonstrating that the species of Pseudo-nitzschia Toxin-producing cells were present in high concentrations in that year’s episode.
The three marine biologists who carried out the research analyzed the content of specimens of the herbivorous zooplankton that feeds on diatoms collected by the sampling that oceanographic vessels routinely carry out in the bay.
And so they were able to reconstruct the regional phytoplankton of 1961. The species of Pseudo-nitzschia Toxin-producing cells accounted for 79% of the digested diatoms in the zooplankton samples. Among the six species of Pseudo-nitzschia found two stood out: P. australis Y P. multiseriescausing the flowering that, thirty years later, also drove the brown pelicans crazy.
On the other hand, if the oceanographic data of the movements of the oceanic surface waters in Monterrey are analyzed, it can be observed that the conditions of the currents in 1961 were very similar to those registered in 1991.
Alfred Hitchcock probably never knew that behind one of the most awe-inspiring scenes in his work were “supercharged” diatoms, which continue to wreak havoc.