The parrots, brought to Europe and Israel as pets, have established numerous wild populations. Most of the species in Europe are ring-necked and monk parakeets, although there are several other species establishing populations.
There are over 10,000 ring-necked parakeets and monk parakeets in Israel, according to Dr. Assaf Shwartz of the Faculty of Architecture and Town Planning at the Technion-Israel Institute of Technology.
"These are parrots that were brought to Israel as pets and some of them were released or escaped from their cages and created huge free populations," explained Shwartz.
While introduced parrots can damage the environment wherever they are, severe impacts are rare and localized. Most reports of damage were caused by widespread and locally abundant ring-necked and monk parakeets.
While the birds cause large crop losses in their native areas, in Temperate Europe no comparable widespread and severe damage has been recorded. In Mediterranean Europe, however, these effects have been reported.
The more serious issue presented by the invasive avians is competition with native species. In the Americas, monk parakeets can damage power infrastructure with their stick nests, but these problems have not made much of an appearance in Europe.
Other species of parakeet have not made much of an impact in Europe, but this is most likely because they currently make up relatively small and localized populations.
The study added that the generalized threat level posed by invasive species is often based on their worst known impacts, while they in reality can often only cause damage in specific circumstances. Because of this, including damage reports from the native range or from other invaded ranges typically results in higher threat level estimates compared to what has actually been observed in Europe.
Shwartz added that ring-neck parakeets and monk parakeets have already established large populations in Israel and Europe. "Ultimately, the decision on ways to reduce the damage is in the hands of the decision makers, but as scientists, it is important to note that the best way to combat species invasions is to prevent the release of non-native species in nature," said Shwartz.
While studies have shown that its possible to eradicate or mitigate invasive populations on islands, it is often not an option on large continents in areas such as Israel and Europe. "There is no ‘silver bullet’ solution to the problems, so it is important to conduct wide cost-benefit studies before taking various measures," concluded Shwartz.