From Beat in Switzerland:
   
the idea of Windowzoo is simple. you know those bird-stickers one uses to scare birds away from big glass-surfaces (so they won’t fly into the glass)? my firned started making his own bird-shapes out of sticky foil, and keeps putting them up on various locations all around the world - but almost always on glass, also besides the “boring” standard-stickers. As this is non-destructive art only visible to those with keen eyes and a sense for discovering the unusual, it remains exhibited longer - and generates more buzz among those in the know.

right now there are 169 birds in 55 cities all around the globe. have a look at the worldmap showing the locations that he put up in the “about” section.