What links a film starring Katharine Hepburn, Jimi Hendrix, bits of a plane falling on to Syon Park in London and the great storm of 1987? The answer is that they’ve all been proposed as the origin of one of Britain’s loudest, most colourful and recognisable birds: the ring-necked parakeet. Parakeets are unusual among British birds in that they actually need an origin story. A century ago, there were none flying free in Britain and, as recently as the early 1990s, parakeets were relatively hard to find in the country. There were only a couple of reliable sites – the leafy Berkshire village of Wraysbury, or the trees around Esher rugby club in Surrey – where they would roost on winter evenings. Since then, their population has exploded into the tens of thousands. They’ve spread across the country from Plymouth to Aberdeen, and even over the water to Northern Ireland. London is their stronghold, though, and it’s increasingly rare to venture outside without hearing their raucous cries or seeing their long-tailed silhouettes skimming the rooftops. Where did they come from? Parakeets naturally live on the Indian subcontinent and across northern Africa, but at some point they were released or escaped from captivity in Britain. Perhaps the best-known “origin story” is that Jimi Hendrix released a pair of parakeets, named Adam and Eve, on Carnaby Street near the end of the 1960s. It’s unlikely they spread, as it’s very unusual for a population to arise from just a single pair. The story that some parakeets escaped in 1951 from Shepperton Studios and the set of the Hepburn and Humphrey Bogart film, The African Queen, is more credible (Shepperton is midway between Wraysbury and Esher). The only problem? The African Queen was actually filmed at Worton Hall studios, near Twickenham. We can rule out the other explanations. Parakeets were established in Britain before the 1970s, which means they were neither brought here by the great storm of 1987 nor emerged after plane debris broke open aviaries at Syon Park at some point in the 1970s. Working out the source of Britain’s parakeets has become a scientific detective story, so it’s appropriate that the researchers trying to do this (including me) have borrowed a technique from criminology: geographic profiling, or GP. This method helps detectives to pinpoint the likely home of a serial offender given the scenes of their crimes. Scientists can use it too, for things like identifying the source of a disease outbreak or the origin of a population of alien species. Parakeets, for instance. GP shows that neither Carnaby Street nor Worton Hall studios are likely to be the starting point for Britain’s parakeets. They probably came from releases or escapes from more than one place. The most likely spots, according to the findings of a study using GP that was conducted in 2019, place them near Croydon in Greater London and Dartford in Kent. This raises another question – why were there multiple releases of parakeets in different areas? We can find evidence to answer that in newspaper archives. Searching for articles about parakeets reveals that in the early 1950s, Britain was gripped by a health scare: psittacosis, or parrot flu. Psittacosis can be caught from pet birds and can be fatal. It seems that many parrot owners didn’t want to take any chances. Their options would be to have Polly put down or let her go. Many people presumably chose the latter. The liberated parakeets clearly found London to their liking. Their descendants throng the city today, and have used it as a springboard to colonise the rest of the country. Parakeets are now part of the British avifauna, but they are technically aliens and they have spread, which makes them an invasive species. Many such species are a cause for concern because of their impacts on the environment or the economy. Japanese knotweed, ash dieback, the Asian hornet, and the Colorado beetle all spring to mind. Should we be worried about the parakeets too? Unfortunately, the answer is probably yes. We know that parakeets can have negative impacts on other birds and bats, competing with them for food and nesting sites. Another concern is their appetite for flowers, fruits and seeds. I’ve watched them stripping blossom from trees in spring and apples in autumn. At the moment, parakeets live mainly in cities, but they may eventually give Britain’s soft fruit and growing wine businesses cause to worry. At first, parakeets were a curious addition to the local flora or fauna. A few parakeets – what’s the harm? We may only discover the true answer to that question when it’s too late to do anything about them. Love them or hate them, parakeets are probably here to stay. Tim Blackburn is professor of invasion biology at UCL and author of The Jewel Box: How Moths Illuminate Nature’s Hidden Rules