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IT鈥橲 MINUS 13掳C in Fargo, North Dakota, and I鈥檓 talking to a woman about tropical . Page Klug, a biologist at the National Wildlife Research Center鈥檚 (NWRC) field station there, has recently taken a keen interest in the squawky invaders. Not, she stresses, because they have got as far as North Dakota 鈥� not yet, anyway. But because she is a leading researcher on agricultural pests of the avian variety and her expertise is in demand.

To Londoners like me, this will come as no surprise. When I moved to that city three decades ago, ring-necked parakeets were a rarity, an occasional raucous flash of green in a park. These days it is a rare walk through the urban jungle that doesn鈥檛 feature an encounter, and the city is now as famous for its parakeets as for its pigeons. 鈥淭he population has really taken off,鈥� says Tim Blackburn, a biologist at University College London. 鈥淧retty much anywhere you go in London you can鈥檛 miss them, and they鈥檙e obviously spreading very rapidly.鈥�

What is happening in my backyard turns out to be happening all over the world. A decade ago, it was mostly a European problem. Now, more than 35 countries, from the US to Israel and most recently Azerbaijan, are experiencing an explosion in their populations of alien parakeets. This makes these birds among the and, like other invaders, they are increasingly making a nuisance of themselves. How did these showy creatures from the tropics spread so far and wide? What does their success tell us about the world we are creating? And can anything be done about them?

Even before it started its world tour, the range of the ring-necked parakeet (Psittacus krameri, also known as the rose-ringed parakeet) was extensive. When first , the species inhabited a band right across sub-Saharan Africa, from Gambia to the Horn of Africa. In the early 20th century, a separate subspecies, Psittacus krameri borealis, was described living on the Indian subcontinent. It is this population from which the European parakeets are descended, according to genetic evidence.

They probably arrived as pets. In the UK, the first recorded sightings in the wild were in Norfolk in 1855, but the birds don鈥檛 seem to have survived for long. A breeding pair with five offspring was reported living in a tree in Lincoln鈥檚 Inn Fields in central London in 1886, but again didn鈥檛 persist. The first long-term wild populations were established in Kent in the late 1960s, and by the 1970s there were small colonies in counties around London. The first northern populations were established in Greater Manchester around this time too. Now, parakeets can be found in Scotland and there have been a few sightings in Wales, but they have yet to make it to Ireland.

There is no shortage of colourful stories about how they got here. Some involve Hollywood goddesses, rock gods or even acts of god, but all are almost certainly apocryphal (see 鈥�Just so stories鈥�). The prosaic truth is that there was no single founding population. The birds probably escaped 鈥� or were released 鈥� from captivity in dribs and drabs over many years. Parakeets are expert escapologists and break out of cages and aviaries all the time, says Richard Bufton at the University of Birmingham, UK, who researches their spread.

The population remained in the low hundreds until about 1986, then exploded. The most recent census, from 2012, put the number of breeding pairs in the UK at 8600. 鈥淚t鈥檚 likely to be a lot more now,鈥� says Bufton. He maintains a register of sightings and reckons there are about 30,000 individuals across the country, which officially makes the ring-necked parakeet a . What鈥檚 more, numbers now appear to be rising by about 30 per cent a year.

Exactly what caused the upswing isn鈥檛 clear. 鈥淚 suspect it鈥檚 partly a natural stage of population growth,鈥� says Blackburn. 鈥淧opulations often bounce along at relatively low levels, then reach a point at which they grow much more quickly.鈥� It may be that a recent escapee introduced new genes into the population, which increased individuals鈥� chances of survival in their new environment.

Perhaps this was an adaptation to the cold. Blackburn points out that ring-necked parakeets live quite happily in the foothills of the Himalayas, so must already be adapted to cold to some extent. But not fully. 鈥淵ou often see them with missing toes as a results of frostbite,鈥� says Bufton. He thinks that parakeets exploit the urban heat island effect to cling on through the winter months, which in the UK means living in or near cities. The most northerly outpost they have conquered in the world so far is Glasgow. The recent arrivals in Baku, Azerbaijan 鈥� where midwinter temperatures hover around freezing 鈥� appear to survive by roosting near oil refineries that burn waste gas.

For now, invasive parakeets are considered synanthropic, meaning that they live in close proximity to humans so as to exploit artificial habitats such as heat islands and bird feeders. But climate change could alter that. 鈥淢y suspicion is that as the climate generally warms, and particularly as winters get milder, there are probably more birds making it through the winter and that鈥檚 helping the population to grow,鈥� says Blackburn. 鈥淚ncreasingly, I think we鈥檒l see them outside the cities.鈥� They will probably spread even further north. So, there may yet be life in Monty Python鈥檚 parrot 鈥� there is a blue variety of ring-necked parakeet.

Their further spread is an intriguing prospect, but no joke. 鈥淎lien species are one of the primary ways that humans are changing the natural world,鈥� says Blackburn. 鈥淯nderstanding that invasion process is very important for understanding environmental risks humans are posing.鈥�

鈥淲ith 30,000 parakeets in the UK, they are officially a common bird there now鈥�

In the US, parakeets have already expanded beyond cities: southern states, including Alabama, California, Florida, Louisiana, Texas and Virginia, have . And they are increasingly troublesome. 鈥淭hey have the capability of becoming serious agricultural pests,鈥� says Klug. The birds naturally eat fruit, so flock to fruit trees, but they also devour nut and seed crops. They are destructive, wasteful eaters. 鈥淭hey鈥檒l pick something up, give it a peck, ruin it for sale, but then drop it and move on to something else,鈥� says Jim Groombridge at the University of Kent, UK.

, but there is growing concern that expanding parakeet populations are putting a squeeze on native wildlife. Invasive species are one of the leading causes of biodiversity loss, and parakeets compete with other species in several ways. For a start, they nest in tree hollows. 鈥淭hey occupy nest sites much earlier than British birds do,鈥� says Bufton. That can leave birds that nest in tree holes, like nuthatches and woodpeckers, with nowhere to go. 鈥淭his is one of the reasons why they are so successful,鈥� he says. 鈥淭here鈥檚 also some evidence that they push certain native species off bird feeders and therefore potentially have impact through competition for food,鈥� says Blackburn. In southern Spain, meanwhile, the parakeets are , Europe鈥檚 largest bat, which is classified as vulnerable to extinction. The birds usurp its nesting holes in trees and sometimes peck the bats to death.

There is also a growing realisation that parakeets can be a reservoir of pathogens. They carry some diseases found in livestock, although there is no evidence that they pass these on to them, says Blackburn. However, pet parakeets do sometimes transmit a flu-like infection called ; an outbreak of this 鈥減arrot fever鈥� in France in 1930 apparently caused some owners to release their birds into the wild, which has been proposed as the origin of the European population.

Noise pollution

Another growing problem is the squawking. Parakeets are noisy birds and when they mass together in roosts they can be cacophonous. There are anecdotal reports of people being kept awake at night or being unable to sell their houses because of parakeet noise pollution, says Groombridge.

If you want to see the damage parakeets can do, look to Hawaii. Ring-necks arrived on Oahu island in the 1930s and found the conditions to their liking. For years they were little more than a curiosity, but now they are becoming a serious pest. 鈥淧arakeet populations can have these really long lag times where they鈥檙e not a problem. Then numbers start to increase exponentially,鈥� says Klug. This is what has happened in Hawaii in the past two decades. By 2018, there were approximately and a further 6800 on Kauai. 鈥淭hey are really starting to show an impact on agriculture and tourist resorts, with their faecal and noise pollution,鈥� she says. Many people have had enough. 鈥淚 think that the level of damage has reached a point that there is support for controlling that population,鈥� says Klug.

Eradicating Hawaii鈥檚 parakeets wouldn鈥檛 be easy, though. There are essentially two options: the gun or the pill. Shooting is quick and deadly but hard to do safely when there are people and other animals around. Contraceptive-laced bait has proven effective in the lab, but is difficult to roll out in the wild, as you have to design feeders that are accessible only to your target species. Even then, parakeets are long-lived, so a contraceptive-led eradication programme may take 20 to 30 years. And there is a fear that a control programme could make things worse by driving parakeets out of the agricultural lowlands and into the highlands, where they could pose a threat to Hawaii鈥檚 endangered native birds. 鈥淭hey can be aggressive, so there鈥檚 a conservation component that we鈥檙e concerned about,鈥� says Klug.

鈥淎t this point, with the numbers that there are, the effort is going to have to be long and sustained to be able to even bring their populations down,鈥� says Klug. However, there is a precedent. Last year, Seychelles announced the from its main island, Mahe, after an . The last of around 500 birds was shot in 2017 and none have been seen since then. 鈥淚t鈥檚 the one successful campaign,鈥� says Klug.

As yet, there is little appetite for parakeet eradication outside Hawaii and Seychelles. Nevertheless, biologists are beginning to advocate control programmes in some areas where the bird isn鈥檛 yet a pest. California, for example, with its almond, pistachio and fruit farms, is considered especially vulnerable to invasive parakeets. In a recent , Klug鈥檚 colleague Aaron Shiels at the NWRC field station at Fort Collins, Colorado, argued that California should consider controlling parakeets while it still can.

In Europe 鈥� and especially in Britain 鈥� that probably isn鈥檛 an option. The genie is already out of the bottle; parakeets are just too abundant and spreading too fast to control. 鈥淚 suspect as time goes on, we will wish we鈥檇 done something about them 40 years ago,鈥� says Bufton. 鈥淚 think the time for eradicating them is long gone.鈥� Besides, killing parakeets would be controversial. 鈥淎 lot of people love them. I love them. I think they are awesome birds,鈥� he says.

But sentiment can turn. 鈥淢any people love seeing them in their gardens,鈥� says Groombridge. 鈥淏ut once they hit a certain threshold, where suddenly all you鈥檙e seeing is parrots in your garden鈥� It鈥檚 interesting how people鈥檚 perceptions change.鈥� If familiarity breeds contempt then, like London鈥檚 maligned pigeons, parakeets may one day be regarded as flying rats.

Even if ring-necked parakeets were to go the way of the dodo, that wouldn鈥檛 necessarily end Europe鈥檚 parrot problem. There are many similar species that could take their place. The monk parakeet 鈥� a cold-adapted native of South America 鈥� is already out of control in some cities, including Barcelona in Spain. The from India 鈥� which looks just like the ring-necked but with a purple patch on its shoulder 鈥� is already in the UK, Belgium, Germany and Italy.

鈥淭here are about a dozen, if not more, parrot species that have breeding populations in Europe and which are classed as potentially invasive,鈥� says Groombridge. 鈥淭hey鈥檙e waiting in the wings.鈥�