A purge of the parakeets that have colonised parks and gardens in London, Surrey and Kent is being considered by the Government.
A study of the problems posed by 30,000 rose-ringed parakeets, originally from India and sub-Saharan Africa, has been commissioned by the Department for the Environment, Food and Rural Affairs.
Bird watch: Ring-necked parakeets are a regular sight in parts of London and the Home Counties
Some ornithologists believe that the parakeets are competing for food and nesting space with native birds.
Others, including the Royal Society for the Protection of Birds, remain unconvinced that there is an impact on native wildlife. However, they say there are signs that the population is rising and could be about to spread.
Tony Drakeford, an ecologist who lives near Bushy Park in south-west London, where the parakeet population has grown by 30 per cent in the past year, said: "They are very pretty and exotic but are having an impact on our woodland tree-crevice nesters. Something needs to be done but the options are complicated."
Tim Webb of the RSPB said the charity had yet to be convinced that parakeets were a problem for native species but if they were, shooting was the only sensible option. A parakeet is larger than most garden birds "so should not prove too difficult". Even so, he said, many people would be distressed to see the birds shot.
One theory about how the birds came to this country is that a flock escaped from Shepperton Studios in south-west London during the filming of The African Queen in 1951. In fact, the RSPB says there are records of parakeets in Britain in 1850.A spokesman for the Department for Environment, Food and Rural Affairs said:
"We are looking at ways of working with the RSPB and others to tackle this problem."