Incorporation of cigarette butts into nests reduces nest ectoparasite load in urban birds: new ingredients for an old recipe?

Abstract

Birds are known to respond to nest-dwelling parasites by altering beha-viours. Some bird species, for example, bring fresh plants to the nest,which contain volatile compounds that repel parasites. There is evidencethat some birds living in cities incorporate cigarette butts into their nests,but the effect (if any) of this behaviour remains unclear. Butts fromsmoked cigarettes retain substantial amounts of nicotine and other com-pounds that may also act as arthropod repellents. We provide the firstevidence that smoked cigarette butts may function as a parasite repellentin urban bird nests. The amount of cellulose acetate from butts in nests oftwo widely distributed urban birds was negatively associated with thenumber of nest-dwelling parasites. Moreover, when parasites were attractedto heat traps containing smoked or non-smoked cigarette butts, fewer para-sites reached the former, presumably due to the presence of nicotine.Because urbanization changes the abundance and type of resources uponwhich birds depend, including nesting materials and plants involved inself-medication, our results are consistent with the view that urbanizationimposes new challenges on birds that are dealt with using adaptationsevolved elsewhere.