Cigarette butts help urban birds ward off mites
- 13:03 05 December 2012 by Joanna Carver .
It's not just people that have a penchant for cigarettes. Birds living in urban environments often use cigarette butts to line their nests. Unlike in humans, the cigarettes seem to have a beneficial effect – they cut the number of parasites in the nests.
Nicotine-based sprays are already used on some crops to repel insects. To see whether cigarette butts might have a similar effect in urban birds' nests, Constantino Macías Garcia from the National Autonomous University of Mexico in Mexico City and colleagues lured parasites to these nests.
The team set up thermal traps in the nests of 27 house finches and 28 house sparrows, species commonly found in cities. The traps had electrical resistors placed on either side of the nest to generate heat, attracting parasites – such as mites – which then got stuck to a strip of adhesive tape attached to the resistor. The team also placed cellulose fibres from smoked or unsmoked cigarettes on top of each resistor to see whether the mites had a preference for either.
Once any chicks had left, the nests were collected for analysis. The team found that the more cigarette fibres the nest contained, the fewer parasites moved in.
What's more, traps containing cellulose from used cigarettes butts attracted 60 per cent fewer mites, on average, than ones with unsmoked cigarettes. This suggests it is indeed the nicotine and other chemicals in a cigarette that repel mites, since these substances are only released once it has been smoked.
Does that mean birds line their nests with cigarette butts to repel parasites? Not necessarily, says Macías Garcia. "One possibility is that the birds are using the cellulose from smoked cigarettes for its thermal properties, as a substitute for other materials such as feathers, down or fur," he says.
"Much of the work on urban environments has focused on the negative impacts of human activities on birds and other animals," says Paige Warren of the University of Massachusetts, Amherst, who was not involved in the study. "But there are also many resources that humans provide for animals in the city."
The team's next step is to determine whether birds that had a choice between spent butts and unsmoked cigarettes would prefer the former. Birds can distinguish between the two by their smell, and if they prefer to line their nests with spent butts, that would suggest they are aware of the butts' ability to deter parasites. The team also plan to investigate whether the chemicals in spent cigarettes harm the birds.
Dave Shutler, a biologist at Acadia University in Wolfville, Nova Scotia, Canada, described the study as "very interesting", but says its results are only vaguely suggestive.
As for the birds' preferred brand, the nests contained more Marlboro Red butts than any other brand. Montserrat Suárez Rodriguez, who co-authored the study, says she doesn't know if that's because the birds prefer Reds or because the students do.
Biology Letters, DOI: 10.1098/rsbl.2012.0931