A study conducted in Mexico suggests that local birds living in urban areas may be using discarded cigarette butts to protect their nests from parasites.
A team of researchers from Mexico City's National Autonomous University of Mexico (UNAM) concluded that bird nests constructed using cigarette butts have significantly fewer parasites than other nests.
Montserrat Suarez Rodriguez, a biologist who co-authored the study, says it remains unclear whether birds are using cigarette butts for the nests because of their effect on parasite levels or because they are readily-available in urban areas and make good material for making nests.
"I was curious about why they utilized cigarette filters. But I want to make clear that I still don't know if they use them because they know they have an effect, or because the material works for them and is available in the city. Here on campus, it is common to find cigarette butts on the ground. The material is very available to birds, and the material is good for building nests," she said.
For the study, the team examined 27 nests built by house sparrows and 28 built by house finches on UNAM's main campus. The two species are among the most birds in North America.
For their nests, birds often use plants that repel parasites. The UNAM researchers found that birds that live in urban areas use discarded cigarettes in much the same way, intentionally or not, as the chemicals used in cigarettes, cellulose acetate in particular, are also known to drive away parasites.
"I wanted to see whether this had an effect on the number of ectoparasites in the nests. Ectoparasites are dangerous to birds, because they feed on the bird's blood and feathers at an important stage of their lives as they are growing and developing to become independent," Suarez Rodriguez said.
During the experiment, researchers installed heat traps in bird nests which were built with smoked and un-smoked cigarettes, as well as cellulose fibers and adhesive tape to trap parasites. The heat traps were installed to collect parasites.
Nests built using smoked cigarettes were found to have significantly fewer parasites, as the cellulose they contain has higher levels of nicotine than un-smoked cigarettes.
Nicotine has historically been used as a parasite-repellant in certain crops, and for the control of parasites in poultry.
The study notes that birds may use cigarettes due to the similarities between the cellulose in cigarettes and green plant materials that would otherwise be used to construct nests, as well as due to their abundance and availability to birds that have adapted to urban environments.
Additionally, researchers noted that cigarettes may have chosen cigarettes because of their insular properties rather because of the protection they provide against parasites.
The UNAM research team believes further tests will be necessary to properly determine whether birds are making a conscious decision to seek cigarette butts, and, if so, why.