Horned Larks are cute little songbirds with white bellies and yellow chins—at least, now they are. A hundred years ago, at the height of urban smoke pollution in the US, their pale feathers were stained dark gray by the soot in the atmosphere. A new paper in the Proceedings of the National Academy of Sciences shows that the discoloration of birds in museum collections can be used to trace the amount of black carbon in the air over time and the effects of environmental policy upon pollution.