Birds Use Cigarette Butts to Ward Off Pests

Urban birds are using cigarette butts to ward off pests from invading their nests, suggests a new study.

A team of researchers led by Constantino Macias Garcia from National Autonomous University of Mexico in Mexico City, have found that birds are using the repellent properties of chemicals like nicotine in smoked cigarette butts to protect their nests from parasites.

The research team studied nests belonging to house sparrows and house finches in Mexico City. Whilst sparrow nests had an average of eight cigarettes each, nests of finches contained at least 10 cigarette filters on an average.

When the team measured the amount of cellulose (an element present in the cigarettes) in the nests, they found that the nests with more cellulose contained lesser parasites, according to a report in Nature.

Experts also placed thermal traps in the birds' nests to generate heat and attract the mites. They also attached cellulose fibers from smoked or unsmoked cigarette filters to the traps and used a tape to catch the insects.

They found that the devices attached with cellulose from unsmoked butts attracted more mites than cellulose from smoked butts. This suggests that nicotine and other chemicals in cigarette butts are keeping mites off from invading nests.

"It appears that this effect may be due to the fact that mites are repelled by nicotine, perhaps in conjunction with other substances, because thermal traps laced with cellulose from smoked butts attracted fewer ectoparasites than traps laced with non-smoked cellulose," the researchers wrote in the paper.

"This novel behavior observed in urban birds fulfils one of the three conditions necessary to be regarded as self-medication: it is detrimental to parasites."

Birds are known to line their nests with plants that contain pest-repellent chemicals, but the urban birds are using cigarette filters to line their nests. This sheds light on how urban birds have adapted to the changing environment, said the researchers.  

Experts are further planning to study whether the birds have any preferences when they are given a choice of using smoked and unsmoked cigarettes. In case the birds prefer to line their nests with smoked butts, it would suggest that the birds are well aware of the butts' ability to ward off parasites, reports NewScientist.

The research team will also be examining if the chemicals in cigarette butts have any negative effect on the birds.

The findings of the study are published in the Royal Society journal Biology Letters.