Cigarrette butts on the floor, one of the most common and bothering rubbish in cities are not completely dangerous,therefore at least for some urban birds as it's shown in the research performed in the City of Mexico which proves that a lot of different birds use this rubbish to keep their nests free of parasites. The discovery is part of a duty directed by the mexican scientific Constantino Macías García, which was published on Wednesday by the british Royal Society. “The research concluded that cigarrette butts are behind a decrease in the number of parasites such as acarus or louses which suck bird's blood and feed on their feathers”, pointed the scientist. The study developed in Mexico and grants interesting examples about how do birds to adapt to their urban environment as posted on the Biology Letters published by the Royal Society.