How can I stop birds from hitting my sunroom windows?
There are two reasons birds fly into Windows, either they can't see the glass or they see a reflection in the glass.  The only real solution, is to make the window more visible or less reflective.  Unfortunately, making the window more visible to birds also makes it more visible to humans.  So the solution may not be exactly... um... fashionable.  You'll have to put decals, tape, paint, marker, or some other type of markings on the windows.  You could also try hanging wind chimes, or other decorative items inside/outside the window.  Some sources recommend decals in the shape of birds of prey, stating that the birds will be afraid to fly towards the the "prey bird".

Another solution that seems to be successful, is to hang fine mesh over the windows.  The theory here is that the mesh will reduce the reflection on the windows, so birds will be less likely to fly into the window thinking they are flying into whatever is reflected in the window.

The good news is, you may only need to do this during migratory seasons.  So you could pick up a window paint marker (~$5.00), and draw lines, squiggles, or patterns on the windows during migratory seasons. 

 

You could try making up some detachable screens for the exterior of the windows, and put them up during the migration season.  This might be a less noticeable solution, while also being temporary.