Birds are lining their nests with cigarette butts to repel pests and keep themselves warm, according to research.
Wild birds have long protected their nests from mite invasion by importing chemical-emitting plants, reports the Daily Telegraph.
But now birds living in cities seem to have adapted similar behaviour, filling their nests with up to 48 cigarette buts to make use of the repellent properties of tobacco.
The nicotine and other chemicals in discarded filters act as a natural pesticide that repels parasitic mites. At the same time, the cellulose butts provide useful nest insulation.
Scientists in Mexico City studied nests of house sparrows and house finches that each contained, on average, about 10 used cigarette butts.
Birds who stored larger numbers of butts saw their nests significantly less infested by mites.
Dr Constantino Macias Garcia, from the National Autonomous University of Mexico, and his team wrote in the Royal Society journal Biology Letters: "This novel behaviour observed in urban birds fulfils one of the three conditions necessary to be regarded as self-medication: it is detrimental to parasites."
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