Window Cleaning after Bird Attacks!

Over the years I’ve seen a few bird hit windows with an image so cool you almost hate to clean it.
 
Always assumed it was dirt, but this BBC article says bird silhouettes are left by the bird’s “powder down” – a substance protecting growing feathers.
http://www.bbc.co.uk/news/uk-england-cumbria-14111152
 
And here’s a photo gallery
http://www.bbc.co.uk/news/14119607
 
Thanks,
 
Gary Mauer
Window Cleaning Network
Oconomowoc, Wisconsin
 
www.window-cleaning.net