Glasgow's wild parakeet flock is colourful and popular with the locals but their days may be numbered.
About 20 or 30 of the birds have made their home in Victoria Park in the west of the city.
Stan Whitaker of Scottish Natural Heritage said he believed they were the most northerly flock of parrots in the world.
"Surprisingly parakeets seem to be very adaptable to different environmental conditions," Mr Whitaker said.
"Almost certainly parakeets were kept as pets and they have either escaped or perhaps been deliberately released."
A parakeet is any one of a large number of small to medium-sized species of parrot that generally have long tail feathers.
Mr Whitaker told BBC Scotland's The Nine: "Invasive species cause impacts on native wildlife, the economy and the way that we live.
"Their droppings can also spread diseases.
"So we can't just think about what the impacts are at the moment, we have to look ahead 40, 50 years into the future and see what impacts are likely to be then."
A study is being carried out by government wildlife agency Scottish Natural Heritage to see if Scotland's only breeding colony of ring-necked parakeets will have to be removed.
Mr Whitaker said: "It would be feasible to catch them and potentially rehome them.
"If we allow it to get much bigger, certainly in London the way that the fruit farmers manage them there is by shooting."
'Joy to watch'
Local resident Susan Harris is a fan of the birds.
She said: "On that day that I first saw a parakeet it really took my breath away.
"It's such a joyous bird. It's a beautiful green, it has a beautiful coral beak. It's just a joy to watch."
She said: "I think to call them an invasive species, why not call them a successful species?
"They are adaptable. There is obviously a place for them in nature and they've come and they've taken advantage of it."