Darkening windows

The tree just outside our large dining room window is full of birds on our feeders... except when we are anywhere near the window! The birds see us and fly away!

My wife's health conditions require darkened windows anyway. 

I want to have film put on the inside of our window but many are reflective. I'm afraid that our birds may see the reflection of the feeders in the window, and injure themselves by flying against the window. 

Any advice on what sort of film I should get put on? Anything I should avoid?