When building a nest, birds tend to make do with the materials at hand—or at beak. Twigs and leaves are popular choices. But what about city birds? Some reach for cigarettes, or at least the fluffy white fibers found in their filters.

 

Scientists got to wondering whether this habit might provide the birds benefits other than comfy bedding. So they grabbed the nests of finches and sparrows that were living on the campus of the National University of Mexico. That’s in the heart of Mexico City. And they found that the nests that were festooned with the most filter fiber had the lowest numbers of mites.

 

Could be that the little bloodsuckers are turned off by nicotine. Or maybe they’ve heard about the dangers of secondhand smoke. But for the birds, a butt a day might just keep mites away.