City birds are snatching used cigarette butts to ward off parasites in their nests. Scientists are learning about surprising ways in which birds adapt to urban environments.The city dwelling birds are reportedly filling their nests with cigarette butts to help repel parasites.Apparently the nicotine and additional chemicals that are housed in smoked cigarette butts serve as a pesticide. Researchers in Mexico City discovered that the nests of house finches and sparrows contained roughly 10 used cigarette butts.They noticed that the nests which contained the most filters were home to a reduced amount of mites. Scientists tested the repellant effect by utilizing heat traps to attract mites, and placing them in the nests of 55 birds. Each trap contained cellulose fibers and either smoked or unsmoked cigarette filters. A little over 15 minutes later, researchers found that the smoked butts had the least amount of parasites attached, as the filters contain more nicotine. Traps which housed unsmoked butts attracted doubled the amount of mites. Birds have been known to bring aromatic plants into their nests to ward off mites and parasites. The chemical properties in these scented plants fight off bacteria, viruses and parasites. Their newest measure of utilizing smoked cigarette filters may be a form of adaptation.