The evening started peacefully enough at Long Lane Recreation Park in the western suburbs of London, disturbed only by the occasional rumble of a distant jet landing at Heathrow Airport.
But just before sunset, five bright green missiles streaked through the air toward a row of poplars at the park’s edge.
Within minutes, hundreds more of the squawking birds — in formations 10, 20, 30 strong — had passed above the tidy homes and a cricket club, whizzing toward their nightly roost.
Individually, any of the rose-ringed parakeets could be the star of a DreamWorks film, electric green with bright pink beaks and the voluble personalities that have long made the tropical species a popular household pet. But for people who frequent the park or live nearby, the visceral experience is more like “The Birds” — albeit with more color and a much noisier soundtrack than the Hitchcock film.
Native to the Indian subcontinent and sub-Saharan Africa, the rose-ringed parakeet is enjoying a population explosion in many London suburbs, turning a once-exotic bird into a notorious pest that awakens children, monopolizes garden bird feeders and might even threaten British crops.
One rough estimate put the population in Britain at 30,000 a few years ago, up from only 1,500 in 1995. Researchers at Imperial College London are now trying a more scientific census through its Project Parakeet, which enlisted volunteer birders around the country for simultaneous counts on a recent Sunday evening.
“I was delighted when I first saw one in my yard, but when you have a flock of 300, it’s a different matter,” said Dick Hayden, a retiree who was volunteering at Long Lane Park. “They eat all the berries. They ate all the food from my feeder in one day; it was ludicrous. I had to stop putting it out because it got too expensive.”
There is wide agreement that the Adams and Eves behind the current population boom did not fly here from Asia or Africa but escaped from British pet cages or were intentionally released by their owners. The great mystery is what allowed the parakeets to procreate with such phenomenal success just in the past decade.
Throughout much of the 20th century, there have been occasional sightings around Britain of escaped parakeets, which are hardy enough to survive the foothills of the Himalayas. But their numbers remained low, and most scientists assumed that they were not adapted well enough to breed readily.
Theories abound. Is it that gardeners are planting more exotic ornamental plants, effectively providing imported food to match an imported bird species? That suburbanites are installing more feeders and putting out more seed? The booming British gardening industry guards sales figures and has provided little guidance.
Alternatively, some scientists suggest that a slightly warmer climate has indeed helped tip the balance, perhaps increasing the parakeet’s metabolism during its February breeding season, bolstering the growth of some of its favored food or killing off a predator.
“Being tropical, they’re used to a milder climate, and they’ve arrived here during a long spell of warm years,” said Grahame Madge, a spokesman for the Royal Society for the Protection of Birds. Yet the parakeets also did fine over the past two winters, which were uncommonly cold.
“The jury’s out,” Mr. Madge said. “I’m not aware of any predators being removed. I’m not aware of any environmental trigger that set this off. I’m not convinced that climate is playing into it.”
Perhaps the answer lies in the numbers game that prevails in any dating venue: once the population passed a certain threshold, it was more likely that each parakeet could find a mate and make a home in the suburbs.
The new bird census may help shed some light on the trend. Scientists, birders and policymakers are “waiting with bated breath for these latest numbers,” said David Leech, senior research ecologist at the British Trust for Ornithology. “It’s absolutely fascinating to have a species come in and proliferate like this; we’ve never seen that before. But we need to know a lot more so we can understand how they’ll spread.”
British officials are watching trends closely since the parakeets have proved major agricultural pests elsewhere, ravaging crops in places like India. So far, they have shown little predilection for leaving Europe’s cities and suburbs for agricultural areas. (Far smaller flocks of rose-ringed parakeets have also arrived in other European cities like Brussels and Amsterdam.)
There is also concern that the wily parakeet will outcompete more restrained British birds like the nuthatch, since both species nest in holes in old trees.
So far British scientists have not documented either problem, said Hannah Peck, a graduate student with Project Parakeet, but they remain watchful.
“I saw one have it in with a jackdaw,” she said, referring to a British crow that is itself no shrinking violet. “The jackdaw lost.” — NYT