As a decorating scheme, this is not one of my favorites.
For those who might be having trouble figuring out what the heck they are looking at, I will explain in just a moment. Those of you who have been there with birds probably know exactly what this is.
This is a 3 paneled glass bay window all covered with newspaper. (Yes, fortunately, we still get some newspapers in print or I would need a lot of cardboard).
I have a male goldfinch hurling himself at his reflection in these windows. I taped up the papers, left it for 3 days, and then a couple of panels fell down. So I thought, well, I will leave the few panels off as a test to see if he comes back. Sure enough, he was back the next morning.
Interestingly enough, I can stand there with the Spoiler and the dog and he will fly away for a moment but then come right back and begin beating himself against the window even if the 3 of us are still there. Only once I block all reflection will he fly off.
I may joke about “bird brain” but this is fairly typical bird behavior–among males. They perceive that the reflection is a rival and they won’t fly off until the rival is eliminated. Obviously, when the “rival” is a reflection, it never will be unless we humans help with that.
I have had to wrap a car mirror in plastic to save a cardinal from his rival.
And I had to take a silver gazing ball in for quite awhile to save a robin from his rival.
So it’s a good thing that the plants in this window are snake plants and don’t need a lot of light! I don’t see myself taking the newspaper down anytime soon.
Gardendaze 
When I was a kid, we put a silhouette of a predatory bird that the finches (or whatever they were) were afraid of in the window. It was literally just a black shape of the offending bird on a white background. Alternatively, the black shape can be cut out of paper. It was not a big silhouette at all. Such silhouettes for a predatory bird that local finches are afraid of might be available online. It would only need to be printed out at the correct scale.
https://www.birdsandblooms.com/birding/birding-basics/stop-birds-from-flying-into-windows/
I do actually have those on all the downstairs windows, particularly on my sun porch where the windows are on the north side and south side and the birds are likely to think that they can fly through without a deterrent. On occasion, they still try, but luckily, they are often just stunned.
This is a slightly different issue that usually just occurs during mating season. That’s why it’s only the males–because they’re trying to vanquish their rivals, so to speak. So once this little guy realizes his rival is gone, I am good to take my lovely newspaper down.
Karla