Their bright green feathers and unmistakable squawk make ring-necked parakeets a striking addition to British park wildlife, but the question of how the tropical birds were first introduced has been a subject of contention.

One urban legend traces their origin to a pair released by Jimi Hendrix on Carnaby Street in 1968; another suggests they arrived in 1951 when Humphrey Bogart and Katharine Hepburn visited London with various animals in tow to film The African Queen, set in the equatorial swamps of east Africa.

Now the question has been subjected to a rigorous forensic analysis for the first time, in research that points to an entirely different explanation: pet owners around the country releasing the birds into the wild, possibly prompted by media coverage of fatal “parrot fever” outbreaks.

Steven Le Comber, who led the research at Queen Mary University London, said: “The ring-necked parakeet has become a successful invasive species in 34 countries on five continents. The fun legends relating to the origins of the UK’s parakeets are probably not going to go away any time soon.”

However, analysis by Le Comber and colleagues based on geographic profiling methods used to track down criminals concluded that Britain’s booming parakeet population has grown from numerous small-scale accidental and intentional pet releases.

The analysis tested other popular theories, including that parakeets kept at Syon Park in west London escaped in the 1970s when debris from a plane crashed through the aviary roof, or that damage to aviaries during the Great Storm of 1987 was responsible. However, none of the suspect sites showed up prominently in the heatmap of more than 5,000 unique records dating from 1968 to 2018.

The research, published in the Journal of Zoology, drew on sightings recorded in the National Biodiversity Network Atlas dating back to the 1960s. When this failed to produce an obvious hotspot of parrot activity, the researchers turned to newspaper archives, and a search turned up thousands of pages of news stories about parakeets written between 1804 and 2008.

The team found numerous sensational accounts of human deaths due to so-called parrot fever, an infection called psittacosis, which has the potential to be passed from bird to human and which can be deadly. In 1932 the Middlesex County Times reported that parakeets had been spotted in Epping Forest and credited the “parrot disease scare” of 1931 for an increase in pet birds being released into the wild.

A 1952 headline in London’s Daily Herald reported calls to “Stop import of danger parrots”, while a 1974 report in the Reading Evening Post described eight people falling sick after the death of a parrot.

Sarah Elizabeth Cox, a postgraduate history student at Goldsmiths, said: “It is easy to imagine [these] headlines leading to a swift release of pets. If you were told you were at risk being near one, it would be much easier to let it out the window than to destroy it.”

Steven Le Comber commented on the findings in August, when the research was submitted for publication. He died in September, aged 53.

• This article was amended on 13 December 2019. An earlier version referred to one of the theories being that parakeets kept at Syon Park in west London escaped in the 1970s when a plane crashed through the aviary roof. It was debris from a plane that damaged the aviary, not a plane itself. This has been corrected.