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https://www.nytimes.com/2026/03/18/scien...=url-share
EXCERPTS: Darwin’s finches in the Galápagos, house finches in Mexico and song thrushes in New Zealand have all developed a curious habit: They put cigarette butts in their nests. Some songbirds in Britain are even nesting in outdoor ashtrays.
A new study adds evidence for why urban birds have picked up this preference, at least in one species: The toxins in tobacco may keep parasites at bay in the nests of blue tits, colorful birds that are found across Europe.
Cigarette butts contain about 4,000 chemical compounds, including nicotine, arsenic, polycyclic aromatic hydrocarbons and heavy metals. These compounds could ward off pests that harm birds and their offspring. The study was published this year in the journal Animal Behaviour.
Blue tits are cavity nesters, building nests in natural hollows or human-built boxes. Their nests are also prime habitat for bloodsucking parasites like ticks, fleas and blowflies that can exploit their captive targets — adults brooding eggs, and helpless nestlings.
So, when it came to cigarette butts and nesting in outdoor ashtrays, the researchers wanted to know whether blue tits could benefit from the pesticidal impacts of tobacco.
[...] The researchers in Mexico City have also shown that the impact of tobacco on nests isn’t limited to parasites. Dr. Suárez-Rodriguez showed that hatching, fledging and immune response in finch chicks improved alongside an increase in butts. But blood cells from nestlings showed evidence of genetic damage from cigarette butt exposure, with the long-term impacts unknown... (MORE - details)
EXCERPTS: Darwin’s finches in the Galápagos, house finches in Mexico and song thrushes in New Zealand have all developed a curious habit: They put cigarette butts in their nests. Some songbirds in Britain are even nesting in outdoor ashtrays.
A new study adds evidence for why urban birds have picked up this preference, at least in one species: The toxins in tobacco may keep parasites at bay in the nests of blue tits, colorful birds that are found across Europe.
Cigarette butts contain about 4,000 chemical compounds, including nicotine, arsenic, polycyclic aromatic hydrocarbons and heavy metals. These compounds could ward off pests that harm birds and their offspring. The study was published this year in the journal Animal Behaviour.
Blue tits are cavity nesters, building nests in natural hollows or human-built boxes. Their nests are also prime habitat for bloodsucking parasites like ticks, fleas and blowflies that can exploit their captive targets — adults brooding eggs, and helpless nestlings.
So, when it came to cigarette butts and nesting in outdoor ashtrays, the researchers wanted to know whether blue tits could benefit from the pesticidal impacts of tobacco.
[...] The researchers in Mexico City have also shown that the impact of tobacco on nests isn’t limited to parasites. Dr. Suárez-Rodriguez showed that hatching, fledging and immune response in finch chicks improved alongside an increase in butts. But blood cells from nestlings showed evidence of genetic damage from cigarette butt exposure, with the long-term impacts unknown... (MORE - details)