A team of ecologists discovered that urban birds may be inserting cigarette butts into the lining of their nests in order to repel arthropods.
The scientists published their findings in the journal Biology Letters. Chemicals in the tobacco leaves are known to repel parasitic mites. Researchers examined the nests of house sparrows (Passer domesticus) and house finches (Carpodacus mexicanus), measuring the amount of cellulose acetate, a component of cigarette butts. The more there was of it, the fewer parasitic mites were found.
Heat traps were used to see whether the repellent effect of cigarette butts was related to their nicotine content or other features. The traps, which use heat to lure parasites close, were fitted with cellulose fibers from smoked and unsmoked cigarettes.
The devices with unsmoked butts had many more parasites than devices with smoked butts, which contained more nicotine. In nests that contained bird eggs, traps with unsmoked butts caught on average more than twice as many parasites.