In what is both a display of ingenuity but also a troubling sign of how humans’ carelessness can affect the habits of wildlife, house finches (C. mexicanus) and sparrows (P. domesticus) in Mexico City are using cigarette butts to ward off parasites from their nests.
Yes, birds are turning to cigarettes to protect their nests.
As reported in Biology Letters, scientists observed birds on the grounds of the National University of Mexico “routinely pulling apart cigarette butts to obtain the filters.” Noting that the birds used the filters in building their nests, Constantino Macias Garcia of the National Autonomous University and his colleagues monitored 57 nests and discovered that, the more smoked cigarette butts per nest, the fewer the parasites.
The sparrow nests contained an average of eight used cigarettes and could have between none and 38. The finch nests had an average of ten used cigarettes, and could have from none to 48.
Life Lines at Science Blogs describes how Garcia and his team found that the smoked cigarettes were more effective in deterring parasites:
Using heating elements to attract parasites, they found that probes covered in “used”, i.e. artificially smoked, cigarette butts attracted fewer ectoparasites than those that were not used. These observations suggest that the birds may be using discarded cigarette butts, which collect chemicals like nicotine, for pest control in their nests.
Nicotine and tobacco indeed have been used in some insect repellents for crops and in warding off poultry parasites.
The cellulose from the cigarettes also helps in insulating the birds’ nests. The finches and sparrows have certainly adapted to their urban environment. Some birds who live in more natural settings use aromatic plants to line their nests, both also, it is thought, to guard against parasites and boost their chicks’ immune systems.
But while the Mexico City birds may be protecting their young from pests, there are certainly side effects from their choice of materials. Comments Life Lines at Science Blogs: “Since eggs are rather porous, the potential health risks for cigarette butt-insulation on developing embryos or adult birds are currently unknown.”
It’s been found that sparrows have to raise the volume of their tweets to be heard in cities due to noise pollution. In Mexico City, in an effort to protect their eggs and chicks, finches and sparrows could also be exposing them (and themselves) to something like second-hand smoke in nests that are less safe than intended.
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