Birds use cigarette butts to line nest RYAN

Summary: The nicotine and other chemicals in the cigarettes discarded filters act as a natural pesticide that repels parasitic mites, and at the same time provide insulation for nest. Some birds are suggest by new evidence that they adapt the same behaviour of wild birds importing certain chemical-emitting plants to protect their nests from mite invasion but instead of certain chemical-emitting plants they used properties of tobacco as repellent. St Andrews University scientists studied nests of house sparrows and house finches that each contained, on average, about 10 used cigarette butts in Mexico City. The number of stubbed-out cigarettes incorporated into the nests ranged from none to as many as 48. Both species nest have significant less mites. To test the parasite-repelling effect, the researchers attached cellulose fibres from smoked and non-smoked filters to thermal traps placed in nests. The result shows fewer parasites were drawn to NESTS traps laced with nicotine-laden smoked butts. Birds could distinguish smoked and non-smoked butts from their scent, just as some birds that use the chemical compounds of plants as defence against parasites appear to rely on olfaction to collect those with effective chemicals.
Opinion: In my opinion I think the birds are smart, to choose something that can be found in urban area as mite repellent. They reused the used cigarettes that people DONT doesn’t want to build it in their nest.  

http://www.bbc.co.uk/news/uk-scotland-edinburgh-east-fife-20607413