Why do these birds build their nests with cigarette butts?
As it turned out, the nests with the most fibres also tended to have the fewest parasites like ticks and mites, the sorts of little buggers that dine on the feathers and blood of developing chicks.
https://www.earthtouchnews.com/natural-world/animal-behaviour/why-do-these-birds-build-their-nests-with-cigarette-butts/