for National Geographic News
Flocks of bright green parrots that drown out traditional birdsong with piercing squawks are becoming a familiar sightand soundin Britain, according to a new study.
Researchers found that the feral parrot population is soaring by 30 percent each year and expect it to hit a hundred thousand by 2010.
The study heightens concerns that the raucous invaders' rise up the pecking order threatens Britain's native bird species. The parrots' appetite for fruit and other crops means they could also become a serious agricultural pest.
The four-year study focused on the rose-ringed, or ring-necked, parakeet (Psitacula krameri), a type of parrot. The study was led by Chris Butler, a biologist at the University of Oxford, England, at the time.
Butler, who now works at the University of the South in Sewanee, Tennessee, said parakeet numbers in Britain have soared from fewer than 500 birds in 1983 to as many as 20,000 today. There are around 10,000 in the London area alone.
Butler says the study uncovered several possible factors behind the population explosion.
The researcher found that pairs of adult parakeets usually produced two chicks each yearnot a single chick, as previously thought. Males were also shown to reach sexually maturity by their second year, a full year earlier than scientists once believed.
Butler also noted that parakeets have no natural predators in Britain. "They live for a very long timeup to 34 years in captivity," he said. "It seems likely [their numbers] will continue to increase for the foreseeable future."
Rose-ringed parakeets are native to the Indian subcontinent and sub-Saharan Africa.
Various tales speculate how the birds first became established in Britain. Some say film studios set parakeets free after they were used on movie sets. Others suggest the birds escaped airport quarantine or arrived as bedraggled castaways that flew ashore after a cargo ship capsized near London.
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