Be careful with your smokes!
One more reason not to smoke, or at least, to use an ashtray rather than tossing live cigarette butts out the window:
Lit cigarette butts don't cause a "lot" of barn fires but they may cause a few. About 20 years ago I got a call from a man who traced a small fire in his barn back to a bird nest.
A house finch had used a cigarette butt (paper and dried plant matter) to add to the walls of its nest, and apparently it was still lit. It burned about 5 feet around the nest area.
Source: Birdwatching column by Gary Bogue, published in Contra Costa Times, 3/07/2007