Study reveals cigarette butts are used for insulation and act as bug repellent

A new study, published in the latest Royal Society Biology Letters, has revealed why so many bird nests incorporate cigarette butts in their construction.

The discovery arose after researchers began studying the effect cigarette butts have on parasites. Isabel López-Rull of the Instituto de Ecología, UNAM, explained the outcome: “When parasites were attracted to heat traps containing smoked or non-smoked cigarette butts, fewer parasites reached the former, presumably due to the presence of nicotine."

As a result, the researchers were then able to clarify why cigarette butts were so useful in nests. "The amount of cellulose acetate from butts in nests of two widely distributed urban birds was negatively associated with the number of nest-dwelling parasites," the authors wrote.

Wild birds have long protected their nests from mite invasion by importing chemical-emitting plants but now birds living in cities seem to have adapted similar behaviour. Some birds have been found to fill their nests with up to 48 cigarette buts to make use of the repellent properties of tobacco.

Birds who stored larger numbers of butts saw their nests significantly less infested by mites. This is due to the nicotine and other chemicals found in discarded filters which act as a natural pesticide that repels parasitic mites. At the same time, the cellulose butts provide useful nest insulation.

The study focused on the house finch and the house sparrow however it is believed other birds are likely to be using cigarette butts in their nests too.