House finches add cigarette butts to their nests to avoid ectoparasites

Submitted by Johan on 12 September 2017.

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House finches in Mexico City break down cigarette butts and use them to line their nests. This may be a response to tick infestation, as these blood sucking parasites are repelled by substances such as the nicotine contained in the discarded butts, but can we be certain?

To answer this, we had to manipulate the nest and the number of parasites within it, but it was uncertain whether the birds would accept artificial, parasite and cigarette-butt free nest linings. While discussing possible alternatives, one of us kept fiddling with his brown felt hat, and that give us the idea; brown felt is soft, pliable, and warm, surely the birds would not mind their original linings being replaced by nice felts cups! They accepted them and we were able to show that, if we sprinkled live ticks, they brought into the nest more cigarette butt fibers than if we sprinkled dead or no parasites.

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