The once-exotic bird is becoming a notorious pest as it enjoys a population
explosion in many London suburbs.
"There is wide agreement that the Adams and Eves behind the current
population boom did not fly here from Asia or Africa but escaped from
British pet cages or were intentionally released by their owners. The great
mystery is what allowed the parakeets to procreate with such phenomenal
success just in the past decade."
Read more at the link