The sight of cigarette butts delicately woven into birds’ nests sparks an array of reactions, from relief that birds are adapting to urban environments to disgust at the display of human disregard for wildlife. But a new study suggests that some birds may benefit from nesting with cigarette butts. The nicotine lingering in filters may serve as an insecticide, driving parasites away from the nests and the baby birds living within.
As horrifying as the idea of baby birds growing up in a cigarette-filled home sounds, it’s not too surprising: the fluffy plastic in cigarette filters makes a fantastic construction material. However, cigarette butts are undoubtably smelly—a fact that has even driven people away from keeping them around.
But birds are actually quite fond of the chemicals found in some smelly plants, otherwise known as aromatics, from which “essential oils” are derived. Aromatic plants produce these chemicals to defend themselves against insects and other animals that would take them for food—but birds have their own use for them. Some nest-building species, including starlings and blue tits, regularly replenish their nests with fresh aromatics, and scientists hypothesize that the birds use these chemicals as parenting tools.
How would plant-derived chemicals help birds raise their chicks? It’s possible that the chemicals boost the immune systems or development of the chicks so that they survive better after they leave the nest; this is known as the “drug hypothesis.” Alternatively, the “nest protection” hypothesis suggests that the plant chemicals act as insecticides, driving parasites and other harmful insects from the nest.