Birds vs windows.

We have a lot of birds in the garden; but by far the majority are house sparrows.  Unfortunately as their numbers have increased, so have the instances of them flying into a particular window; it's a sparrow apocalypse.  I've buried three sparrow and rescued two very unhappy birds in the last two weeks alone.

Has anyone got any experience of sticking things to the windows?  What did you use, and did it work?  I'm pretty sure it's the reflection of the sky and tree for which they're heading.