Unless you're a character from the TV series "Mad Men", you will most likely by now have realised that smoking is bad for your health. It will give you bad breath and wrinkles, not to mention lung cancer. But while this is true for humans, a recent study from Mexico found evidence for birds taking the opposite approach.
As part of her MSc thesis, Monserrat Suárez-Rodríguez and her colleagues from the Universidad Nacional Autónoma de México found that city-dwelling birds add discarded cigarette butts to their nests to repel parasites. It's not the first time this behaviour is reported. Other species in other locations do it as well, which left the researchers wondering whether it was more than just a coincidence.
Nicotine, the main active component of cigarette smoke, is used extensively in agriculture to repel insect pests from crops or against parasites in poultry farming. Arthropod ectoparasites (parasites such as fleas, lice, ticks and mites that live on the body surface of a host) suck blood from warm-blooded animals and can transmit diseases in the process, thus becoming a huge burden on nestlings and adult birds.
For their study, the researchers studied the house sparrows (Passer domesticus) and house finches (Carpodacus mexicanus) living on their Mexico City campus. They attached electric heating devices to nests of breeding birds to attract heat-seeking parasites that were then trapped with adhesive tape. To test whether the nicotine from smoked cigarette butts had any impact, cellulose fibers from smoked and non-smoked butts were compared. After counting the parasites caught on the strips of sticky tape, the researchers could show that thermal traps laced with cellulose from smoked butts attracted significantly fewer mites than traps with non-smoked butts.
In a second step, once the breeding was finished and the birds had left, the empty nests were dissected, weighed and any parasites within identified and recorded. They found that over 80% of nests from both bird species contained smoked cigarette butts, and discovered that they had a clear negative impact on the number of encountered parasites.
The animal kingdom is full of examples of self-medication. Monkeys eat certain plant species after becoming sick, and expecting elephants ingest clay to induce labour. But this is the first report of animals using artificial materials. While it would be a stretch to assume that sparrows and finches deliberately choose smoked butts because of their repellent qualities, this seems to be a new adaptation to an urban environment. Other bird species have been shown to weave green plant material into their nests to repel parasites, so by picking up cigarette butts the birds of Mexico City could be using “new ingredients for an old recipe”.
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