I just found this on a website. I think I'll give it a try.
Top Tip From Texas Parks and Wildlife Service
The best solution I’ve found to this problem is one recommended by Texas Parks and Wildlife Service. It involves drawing grid lines on your windows using fluorescent marker pens (highlighters). It’s cheap and easy to do. It can be done from inside your property so there’s no need to worry about climbing ladders. Best of all, it works!
The pigment in the highlighters can be seen by birds but is difficult for humans to see, so it doesn’t interfere with your view out of the window too much. Drawing a grid of lines with a fluorescent marker breaks up a bird’s reflection, so the repetitive pecking behavior stops. The effect is virtually instant. I use Sharpie Tank Highlighter Marker Pens. Their tanks contain
enough ink to draw a grid over the whole window and their quick-drying ink means that smudging is minimized.
The
video below was made by the Texas Parks and Wildlife Service and demonstrates the difference in bird behavior between a marked window and an unmarked one. It is remarkable the difference a few highlighter lines can make.
Link to page with video here:
DenGarden