A health benefit of cigarettes!: Finches apparently put cigarette butts in their nests to repel ticks

Well, we all know about the deleterious effects of smoking, but it actually has a salubrious effects on some birds—house finches (Haemorhous mexicanus), at least in Mexico City. Mexicans smoke more than do Americans, or so I’ve observed informally in Mexico, so cigarette butts are common. Montserrat Súarez-Rodríguez and a colleague at the Universidad Nacional Autónoma de México observed that both house finches and house sparrows (Passer domesticus) added cigarette butts—or rather, the fibers from them—to the linings of their nests, even though the butts have toxic nicotine in them.

Based on earlier work showing that other species of birds put toxic foliage in their nests to repel parasites, Monserrat Súarez-Rodríguez and her colleague Constantino Macías Garcia suspected that the cigarette butts might have a similar function in finches. Alternatively, the butt fibers could simply serve as insulation for the chicks. They tested these hypotheses, and their results, recently published in the Journal of Avian Biology (reference and free link below), show that the butts seem to be used to repel ticks.

The paper is short and I’ll be brief in summarizing it. Súarez-Rodríguez and Macías Garcia worked on the campus of their university, modifying the nests of house finches that contained newly-hatched chicks. They first removed the linings of the original nests, carefully weighing the cigarette-butt fibers in them and counting the ticks. Then they added artificial linings made of clean felt with a little bit of twigs and grass to hold them in,  These linings were then subject to one of three treatments:

  1. Live ticks added: 70 freshly caught ticks put in the lining (10 nests)
  2. Dead ticks control: 70 freshly caught ticks, but killed by ethanol immersion, were added to each nest in this treatment (10 nests)
  3. No-tick control: no ticks added, but an empty vial was shaken over the nest as a control, as that’s how ticks were added (12 nests; the treatments originally involved 15 nests each, but some linings were lost).

After a period of time (sadly, I can’t find it in the paper), the authors collected the new linings and weighed the cigarette-butt material added during the waiting period.

What they found is that the tick treatments (as well as the amount of original butt material removed from the nests) had a significant effect on the amount of butt material added to the new lining. The strongest effect was not the treatment itself—whether or not there were dead or live ticks, or no ticks, added—but the amount of butt material in the original linings (the more that was originally there, the more was added to artificial linings). But the effect of live parasites over dead parasites, and over the no-tick control, was also significant, suggesting that birds add more cigarette butts to the nest when it has ticks. (Measurement of nest temperatures showed that the butts had no effect.)

Here’s the result of the treatment, showing the grams of butt fiber added to each treatment (the figure caption doesn’t really say what the error bars represent; presumably standard errors; and the circles are presumably outliers, with one of them, in the middle, apparently removed from the analysis):

Virtually no butts were added to the two types of control nests, while an average of 0.2 grams of butt fiber was added to the nests containing live ticks. Presumably, then, the presence of live parasites (and, given the difference between that and the dead controls, birds can distinguish whether ticks are alive or dead—unless tick smell was totally removed by the ethanol used to kill the ticks) did produce the addition of butt fiber. The amount of fiber was small: an average of 0.2 grams, but that may still be a lot of buttstuff.

The authors suggest, then, that butt addition is a way the birds have devised to control parasites, and their finding has gained a lot of publicity (see this piece in New Scientist and the short video they made (below).

The fact that there’s a strong association between butts added and butts in the original lining suggests that birds can actually remember how they lined their nests originally. And although the authors apparently did count the number of ticks in the original nests (mean of 70/nest), they didn’t examine whether original ticks were associated with the amount of buttstuff (were there more or fewer ticks in nests with more butt material?).

They also don’t know whether the butts actually repel ticks. There’s also no indication, nor could there be in this study, whether the birds actually learn to put butt fibers in their nests, have evolved that behavior as an instinctive response to the presence of ticks—or both. There must be some memory involved, given the correlation between original and added butts, but if the behavior has an evolutionary component, it would have had to evolve recently—since the advent of cigarette smoking—and be limited to urban areas. Finally, there’s no data bearing on whether nestlings in nests having more ticks suffer more death or lower later-life reproduction, so we don’t know—though it seems likely—whether these parasites reduce genetic fitness.

Note that the video below says that the butts actually genetically damage birds. Although the original paper doesn’t mention that, the New Scientist piece says this:

However, Macías Garcia’s earlier studies suggest the habit is harmful too. “The butts cause [genetic] damage to finches by interfering with cell division, which we assessed by looking at their red blood cells,” he says.

“I think the anti-parasite effects the cigarette butts provide must outweigh any negative problems they cause,” says Portugal. “Alternatively, the genotoxic effects take longer to manifest, and the adult birds aren’t aware of any problem.”

(Although human red blood cells don’t have nuclei, bird red cells do.) We don’t, however, know if the aberrant cell division they observed reduces the fitness of the birds (that data wasn’t in the original paper). If not, it needn’t be weighed into some kind of net fitness calculus against the presumed reduction of ectoparasites. Such a calculus would be needed to see if the behavior is adaptive.

The study thus has multiple problems, and we’re far from being able to say that the birds put cigarette butts in their nests to reduce harmful parasites. That, however, could be determined with further work, and I hope that this group continues it. It would also be cool to know if this is an instinctive rather than purely learned behavior. If it’s the latter, then the birds are pretty smart!

A sparrow snagging a butt (photo from Trini Lulz):

And a finch nest with butt-fiber lining (photo by Suárez-Rodriguez, at Science News for Students). Note the yellow smoke stains:

h/t: Hempenstein


Suárez-Rodriguez, M. and C. Macías Garcia. 2017. An experimental demonstration that house finches add cigarette butts in response to ectoparasites.  J. Avian Biology, online, DOI: 10.1111/jav.01324


  1. Posted July 2, 2017 at 10:34 am | Permalink

    Fascinating! I’d vote for learned behavior.

  2. Posted July 2, 2017 at 10:42 am | Permalink

    Very interesting!

  3. Posted July 2, 2017 at 11:08 am | Permalink

    I think the plot is a box and whiskers plot, so those aren’t quite error bars. The conventions may differ a bit among plotting programs, but the “whisker” (=”error bar”) extends to the most distant point which is less than 1.5X the distance from the the median to the quartile; the circles (outliers) are points more than 1.5X that distance away from the median.

  4. Gregory Kusnick
    Posted July 2, 2017 at 11:09 am | Permalink

    There must be some memory involved, given the correlation between original and added butts

    Not necessarily. It could simply reflect individual variation in nest-lining preferences. Birds who used butts before used them again after because that’s the kind of lining they like.

  5. Derek Freyberg
    Posted July 2, 2017 at 11:39 am | Permalink

    Nicotine is a potent ectoparasiticide: when I was a child we kept chickens, and my father would paint the touching surfaces of the perches and nest boxes (i.e. where wood met wood, not where wood was exposed) with a product called “Black Leaf 40”, which was a solution of nicotine sulfate. He always wore gloves and was very careful – topical nicotine in high concentration isn’t good for people either.

    • gravelinspector-Aidan
      Posted July 3, 2017 at 3:05 pm | Permalink

      You used to be able to buy liquid nicotine (probably tincture of nicotine, nicotine dissolved in alcohol) at the chemist for use as a slug-icide in the garden. But you had to sign the Poisons Register to get it, and present ID (or be known to the pharmacist).
      I seem to recall a similar study 4 or 5 years ago, possibly in Australia (crows, or corvids of some sort?) to the same effect. Intelligent little theropod dinosaurs, aren’t they.

  6. ThyroidPlanet
    Posted July 2, 2017 at 11:40 am | Permalink


  7. Posted July 2, 2017 at 11:46 am | Permalink

    Very interesting! And it does seem plausible since birds have already been caught using repellent plant foliage for the same ends.

  8. Mark R.
    Posted July 2, 2017 at 11:51 am | Permalink

    Now that is amazing (I assume) learned behavior.

  9. Heather Hastie
    Posted July 2, 2017 at 11:53 am | Permalink

    Interesting stuff. I’d like to know too if plants that repel ticks grow nearby, and if the birds prefer butts to those. Perhaps cigarette butts are easier to harvest or more numerous than the plants, especially in the city. Do the birds normally use tick-repelling vegetation and this is an adaptation city birds have made because needs must?

  10. Michael Fisher
    Posted July 2, 2017 at 12:13 pm | Permalink

    Cigarette butts are “dog ends” in British. Possibly from dock [cut] end or from the last & least pleasing part of something. “the dog end of a hard day”

    Sun streaking cold, an old man wandering lonely
    Taking time, the only way he knows
    Leg hurting bad as he bends to pick a dog end
    He goes down to a bog and warms his feet

    Aqualung by Ian Anderson [the mighty Jethro Tull]

    • gravelinspector-Aidan
      Posted July 3, 2017 at 3:17 pm | Permalink

      Sign erected in about 1 in 5 of Britain’s pub toilets :
      “Please do not throw your dog ends into the urinal.
      It makes them soggy and difficult to light.”

      • Michael Fisher
        Posted July 3, 2017 at 3:34 pm | Permalink

        LOL well up until 10 years ago of course. Now it is a crime to puff away in the bogs.

  11. Phil Rounds
    Posted July 2, 2017 at 12:31 pm | Permalink

    I thought butt-fiber was what you ate to stay regular. I would have called it filter fiber.
    Jeez, i hope i’m getting enough butt-fiber in my diet! :p

  12. loren russell
    Posted July 2, 2017 at 1:35 pm | Permalink

    The birds’ cigarette habit likely dates from the introduction of US-style manufactured filtered cigarettes in Mexico, probably in the early to mid 1950s. To start with, the filter fibers would be much more convenient than ‘traditional’ plant fibers for the nest. Once initiated by a few birds I could see the behavior spreading like the canonical titmouse-cream-skimming — observing other birds’ attraction to nest material.

  13. Posted July 2, 2017 at 4:19 pm | Permalink

    Mexicans smoke more than do Americans,

    That’s strange, I always thought Mexicans were Americans. After all they live in America. Central America.

    (BTW, Full marks to Heather Hastie for coining the term USian.)

    • ladyatheist
      Posted July 2, 2017 at 10:40 pm | Permalink

      Actually, Mexico is in North America.

      • gravelinspector-Aidan
        Posted July 3, 2017 at 3:23 pm | Permalink

        I could probably construct a good argument on geological grounds to classify a significant part of Mexico as part of the Central American tectonic province of an island arc belt behind the Cocos plate’s subduction zones.

        • Posted July 4, 2017 at 1:22 pm | Permalink

          A lot of geographic terms are ambiguous between human geography (and then in various ways) and physical geography (and then in various ways). Consider the perennial question: are Turkey and Russia in Asia?

  14. Filippo
    Posted July 2, 2017 at 4:21 pm | Permalink

    I’m reminded that squirrels have been heavily raiding and absconding with the insulation in the overhead of our little storehouse, with which presumably to line their nests. Fine by me – I don’t care how hot or cold it gets out there.

    • Filippo
      Posted July 2, 2017 at 4:25 pm | Permalink

      And they don’t pay me one red cent for it! 😉

  15. Posted July 2, 2017 at 6:16 pm | Permalink

    Reblogged this on The Logical Place.

  16. rickflick
    Posted July 2, 2017 at 7:26 pm | Permalink

    I think the finches would not be able to learn this behavior(at least not easily) since it’s hard to see how they could associate being tick free with using butt fibers. To learn a behavior you’d expect the cause to be quickly followed by a reward. The reward of being tick free wouldn’t quickly follow nest building.
    I can only think of one way this would work. If the finches had an instinctive way of detecting and preferring material with the same characteristics as butts. Some smell perhaps which is the same as a natural source of insecticide.

    • Gregory Kusnick
      Posted July 2, 2017 at 7:37 pm | Permalink

      Maybe seeing dead ticks is sufficient reward, and one that should follow fairly quickly after putting insecticidal material into the nest. Maybe natural selection has primed the birds to look for dead ticks soon after lining the nest in order to facilitate such learning. This may be a more efficient solution than programming the birds with an innate preference for specific lining materials.

  17. ladyatheist
    Posted July 2, 2017 at 10:42 pm | Permalink

    I suspect it’s learned behavior that’s passed on to the offspring of tick-free nests, and the offspring of tick-infested nests don’t live to make their own nests. Wouldn’t birds want a nest like the one they grew up in? They wouldn’t know it repels ticks since they wouldn’t know what a tick is if their parents’ nest didn’t have them.

  18. Posted July 4, 2017 at 1:23 pm | Permalink

    Is this first example of a non-human species seemingly “deliberately” using a chemical pesticide?

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