Feather dust

The imprints that birds sometimes leave behind after colliding with a window are formed by dust from their feathers. This fine powder is produced by special feathers called powder down. The powder is produced differently in different groups of birds and some species produce more powder than others (for example, pigeons and doves produce a lot).

In pigeons, the small particles of powder are produced from cells that cover the developing barbules on a growing feather. These particles are minute (about 1/1000th of a mm wide), irregular in shape and colourless. Many of the imprints left show an amazing amount of detail as can be seen from the above photograph of a Collared Dove window strike.