Why Birds Around the World All Seem to Be Collecting Cigarettes

From Mexico to New Zealand, Europe to the remote Galápagos islands, researchers have observed an odd behavior of numerous bird species that we are only now potentially beginning to understand: They seem to like to collect cigarettes. Specifically, they gather discarded cigarette butts from human smokers, and they put those butts in their nests, adjacent to the incubating eggs that will soon hatch into chicks. Why would bird species around the world that otherwise have little in common with each other all do this? Why bring something demonstrably toxic, a cast-off of the human world, into the sensitive space where their young will be born? As it turns out, the benefits to the birds may outweigh the risks … or much like human smokers, they may just not be aware of the eventual ill effects.

Researchers in several of these different locales have advanced similar theories for why the birds bring cigarette butts into their nests: The chemical attributes (some of them obviously toxic or poisonous) present in both tobacco and commercial cigarettes may have a repellant effect on insects and other pests that would otherwise be likely to invade a nest. This behavior has been observed in birds such as Darwin’s finches in the Galápagos, house sparrows and house finches in Mexico, song thrushes in New Zealand and Eurasian blue tits in the U.K. A new study of the latter provides some of the first quantified evidence that cigarettes in the nest environment could be having this type of effect.

The blue tits of Europe are cavity nesters, meaning that they choose to build their nests in enclosed spaces, either naturally occurring holes in trees such as those excavated by woodpeckers, or in man-made nest boxes that are erected to give them a place to raise a brood. But such spaces are also vulnerable to pests such as ticks and fleas, which will target both the immobilized adult bird sitting on her eggs, and the chicks after hatching.

In a study of 99 birds that were hatched in three different types of nest boxes, a team of researchers from the University of Lodz in Poland recently demonstrated how the cigarette butts might work to reduce the presence of those pests. They created three groups: Some normal, untreated nest boxes, some that were filled with sterilized nesting material, and some that were otherwise standard except for the presence of two cigarette butts. About two weeks after hatching, samples of the nests were taken and analyzed for their parasite and pest content, and it was found that the nests with the cigarette butts had, on average, fewer invaders than the standard nests, although still more than the fully sterilized ones. Still, it was a result that suggested what other ornithologists and ecologists have come to believe through their observations—including one in Mexico City quoted in The New York Times who said the finches and sparrows of that city were more likely to “dismember the cigarette” to spread its fibers around the nest for greater protection. There, a team of researchers found that the city’s birds filled their nests with far more cigarettes as well, with an average of 8 to 10 per nest.

One has to wonder, however, if this unusual convergence of man-made drug and the natural world could ultimately be doing more harm than good. Give credit to the birds where credit is due: It is remarkable that they would be able to form an association with these discarded human objects and the potential for fewer nest invaders. But we can’t exactly expect the birds to comprehend the potential long-term effects of exposing themselves and their chicks to the more than 4,000 chemical compounds found inside any given cigarette, including arsenic, toxic heavy metals, and of course nicotine. There are blue tits now reportedly nesting inside outdoor ashtrays in the U.K., and I would be rather shocked if that proved to be healthy for those particular feathered friends in the long run.

Indeed, the Mexico City researchers are concerned on that front as well—blood analysis of hatchlings there reportedly demonstrated that the fledglings from nests with cigarette butts had “improved” immune response, but blood cells that showed “evidence of genetic damage from cigarette butt exposure.” It could be that, in oddly fitting fashion given the way that humans have always used cigarettes, the birds are simply embracing a temporary benefit that carries bigger health downsides in their future.

If that’s the case, how do you get a blue tit to kick the habit? I’m not sure D.A.R.E. is going to get through to them.