As horrifying as the idea of baby birds growing up in a cigarette-filled home sounds, a new study suggests that some birds may benefit from weaving the fluffy plastic from cigarette butts into their nests. The nicotine lingering in smoked filters may serve as a natural insecticide, driving parasites and other harmful insects away from the nests and the baby birds living within. (Tobacco plants generate nicotine because it defends against insects and their larvae that would otherwise devour the plants.)

The butts are undoubtedly smelly. But birds are actually quite fond of smelly chemicals, such as those found in aromatic plants. Some nest-building species regularly replenish their nests with fresh aromatics, possibly because the chemicals boost the immune system or the development of the chicks. Alternatively, the plant chemicals might act as insecticides.

In the study, researchers at the Autonomous University of Tlaxcala in Mexico set up heat traps, which attract parasites, in 55 nests around Mexico City. Some traps were lined with filter fluff from smoked cigarette filters. The others were lined with fluff from unsmoked filters, which did not contain nicotine and other smoking by-products. Whether the nest held eggs, chicks or nothing, the unsmoked cigarette traps collected more parasites, suggesting the chemicals drove parasites away and not another property of the filters.

In a second experiment, the researchers collected 28 house sparrow nests and 29 house finch nests from Mexico City immediately after the chicks flew out for good. They found that the more smoked filter fluff padded a nest, the fewer parasites it had.

The missing piece of the puzzle is whether the reduced parasite load in the nests actually provided any benefit to the chicks. It is also unclear if nicotine or another chemical found in cigarettes, such as hydrogen cyanide, arsenic or ammonia, may have turned the parasites out of the nests.

If the results hold, then this study is an example of wildlife adaptation to urbanization—or at least evidence that birds are resourceful and can still follow their noses in urban environments.

Adapted from Culturing Science at blogs.ScientificAmerican.com/culturing-science

This article was originally published with the title Bird Butts.

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