Alfred Hitchcock's 1963 movie, The Birds, is truly a masterpiece of film making, and has often been listed as one of Hitchcock's greatest films.
Loosely based on the 1952 short story by Daphne Du Maurier, The Birds won the Horror Hall of Fame Award in 1991.
But did you know that there was actually some grain of truth in the movie, which influenced Hitchcock greatly when he was putting together the screenplay? That truth related to spates of unusual bird behaviour, which occurred in the spring and summer of 1960 and 1961.
In the La Jolla area of California, in April 1960, hundreds of small birds called Vaux Swifts migrated in a most peculiar fashion.
Instead of their normal tendency of using hollow trees for their communal roosting sites, they swooped down unused chimneys in their hundreds around dusk.
As the spring of 1960 was exceptionally cold, this windy climate was attributed to making the birds concentrate near the coast.
On the 26th April, in the aftermath of some very unsettled weather, huge numbers of these Vaux Swifts were observed in southwestern California.
At the home of a married couple in La Jolla, hundreds of swifts swooped down their chimney and caused complete chaos, flying through every door and passageway that was open in the house like some hellish whirlwind.
One of the birds even became entangled in the wife's hair.
And as if all the damage that these birds had done to the house by their flying everywhere wasn't enough, the horrible smell of bird excrement emanating from everywhere only exacerbated the revolting mess.
Finally, the matter became so bad that the police had to be summoned.
Hitchcock later was greatly inspired by the events of this case, and used it to create the sparrow attacks inside the Brenner house.
The real-life incident involving the bird becoming tangled up in the wife's hair would be replicated in the scene with Lydia Brenner.
He also used other incidents from the true-life case, like the broken ornaments and other damage caused inside the house.
A scene depicting the birds being burned on a bonfire was later deleted.
But a more significant true-life incident involving strange bird behaviour was a source of even greater inspiration to Hitchcock.
This occurred in the seaside town of Santa Cruz, Monterey Bay, on Friday 18th August 1961, not too far from where Hitchcock had a second home.
An enormous flight of sooty shearwaters, fresh from feeding on anchovies, were involved in a collision with shore side structures from Pleasure Point to Rio Del Mar during the night.
The sound of birds slamming against their homes disturbed residents around 3.
00 a.
m.
Police and sheriff's phone lines were subsequently jammed with calls from frightened residents as the birds, vision obscured by thick night fog, flew into rooftops, poles and other obstructions.
Dead and stunned seabirds littered the streets and roads in the foggy, early dawn, blocking traffic.
This scenario was also referred to in the movie, when the people of Bodega Bay are trying to find a reason for the birds attacking, and Mrs Bundy, the ornithologist, tells the story.
The seabird invasion of the coastal town made newspaper headlines, and Hitchcock was quick to react to the news.
He requested that a copy of the newspaper in question, the Santa Cruz Sentinel, be sent to him for research material.
But these weren't the only reported cases of strange bird behaviour.
In some parts of America and England, there were other incidents of birds attacking that helped to add more substance to Hitchcock's screenplay.
For instance, barn swallows attacked newsboys doing their paper rounds in a quiet midwestern town.
Also, in the port of Dover, thousands of gulls left their homes on the white cliffs and swooped down on the town, soiling cars and hitting people who were out walking on the streets.
And in Bodega, farmers told Hitchcock how crows had plucked out the eyes of their newborn lambs.
Hitchcock later used this detail for the attack on Dan Fawcett.