In the Warsaw metro system pigeon droppings mar walls, cover the floors and plop onto passengers' heads ... until now.
Transport authorities in Poland's capital have tapped the killer instinct of birds of prey to deal with the problem.
"Just the presence of a bird of prey inside or at the entrance of a station is enough to act as a deterrent," says Piotr Zadworny, a bird breeder hired by Warsaw subway authorities.
"Pigeons are the natural prey of hawks. They know very well that the appearance of a hawk means their death."
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