In the summer of 1961, seabirds hurled themselves into homes across California’s Monterey Bay, inspiring one of Alfred Hitchcock’s least scary films.

Now, it appears scientists have solved the mystery of the real-life murder of crows behind The Birds. “I am pretty convinced that the birds were poisoned,” biologist Sibel Bargu of Louisiana State University told USA Today.

Bargu and her team investigated by inspecting the stomach contents of turtles and seabirds scooped up during 1961 Monterey Bay ship surveys. The animals’ tummies contained a toxic algae that causes nerve and brain damage. The scientists say the birds that kamikazi-ed Monterey Bay that year likely munched on anchovies and squid packed with the same toxin.

A similar study in 2008 came to the same conclusion, noting that leaking septic tanks from newly-built homes in the area may have fed the toxic algae bloom in the bay.

The American Film Institute ranks The Birds among its top 10 thrillers of the last century.