Summary Asian collared parakeets are increasingly conquering the cities of Central Europe. The green parrots, about the size of magpies, are conspicuous for their loud squawking and large flocks. They litter streets with droppings and are suspected of damaging trees and stealing the nesting cavities of native bird species. In Cologne, ornithologists want to know more precisely whether the accusations are justified.Because of their pretty appearance, parrots were in great demand in the mid-20th century as caged companions. Quite a few specimens escaped from their owners and conquered city parks. They survived the mild winters and reproduced. Birdwatchers estimate the European population at nearly one hundred thousand parakeets.The European Union considers the alien species as potentially invasive. The parakeets with the strong red beak breed in tree hollows and compete with jackdaws and squirrels for nesting sites. In addition, the flocks of skilled birds often leave bare trees in their search for fruits, nuts and seeds.Residents are annoyed. Every evening, large flocks, calling loudly, gather by the thousands at a central roosting site, where they litter the streets with their droppings. Repeated attempts have been made in vain to drive the pests away.A Cologne ornithologist observes the birds in their environment. He finds that the species has adapted amazingly quickly to the new living conditions, and makes astonishing observations that do not fit at all into the opinion picture of the unloved nuisance bird.

• Documentary