I have heard that screens or sheer drapes over windows will help to make it clear to the bird that the window is not an open space. Decals have limited use since birds will still think the rest of the window is open. Maybe have dirty windows? I have had a few birds crash into the big screenless window and a few hummers bang their beaks (but not actually crash) against the glass because they saw flowers on the plants inside.

Maybe a scarecrow or something that flutters in the wind (like a bird scare from a garden supply place) or a "fake owl" on the porch?

Fireraven9
What potent blood hath modest May. - Ralph W. Emerson

Cardinals are notorious for fighting with the image they see in windows, hubcaps, anything reflective. This occurs during mating season but will pass. In the meantime, blocking his reflection with something that will "haze" the glass is about the only solution I can think of. Might want to post on the Birdwatching Forum; lots of knowledgeable folks over there who might be able to help.

I had cardinals break the rearview mirror on my car. They really go crazy when confronted with their own reflection. Ultimately I had the mirror replaced and now cover them with old stockings. One suggestion that I thought was a good one was to hang a mirror for the cardinals to have for themselves, something nearby that may distract them. It seems to be a question of territory, so I am not sure if simply pulling a shade over your windows will work. Good luck!

I hang a hanging glass picture on my windows with a suction cup hanger.

and when the suction cup gives out you can clean all the glass up. My wife hung a decrative stained glass small item to our patio doors and lasted about a month. Guess who came home and had to clean it up and lucky the pets didnt walk through the broken fragments

Dejavu. Just last night, my dad called. Said he had been at the grocery and was bringing the bags in the house. When he walked into the kitchen, he stepped on broken glass!

Seems while he was out, the globe over the light fixture in the kitchen just fell on its own!

His thoughts were to be thankful that (a) he was not IN the kitchen when it fell, and (b) at least it fell during the day when he was apt to be wearing shoes, and not be barefoot.

(Ok not a suction cup story but too weird to read this after getting that call just last night).

The poor bird is trying to protect his territory from himself! He sees his reflection and thinks it's another male and attacks.
Get some BonAmi and a big sponge and put a little BonAmi on the sponge and put it on your window....so it doesn't reflect. Looks awful...but it's only for a little bit. After about a week....just rub it off with a dry towel.
Oh by the way....do it on the outside of the window, beecause when you wipe it off, it will leave some powder....which does no harm outside....but would be a nuisance inside.
Glass Wax would work as well...but I can't get it anymore.
Linda C

I have a funny bird suicide story - well, funny if you're not a bird lover, I suppose... I opened the passenger side door of my van a few years ago and found a dead bird on the passenger seat! Yuck! Gross! It seems I had left the drivers side window down and the birdie decided to take a short cut through the windows.. some shortcut!

Sorry I don't have a solution to the bird crash problem...

We added on a sun room last summer.

I have two imprints above the desk where a pair of doves flew into the glass together. I found one dead one the ground underneath.

Since it is too cold up here to go climb a ladder and clean the windows, the dove imprints remain. (at least until things thaw) They are dirt imprints of the birds.

The birds flew into the room daily when we first built it, they seem to be figuring out that you can not do so and we're having less crashes each week.

Smear the window with something to cut the reflections and wash it off later.

Mom has a picture window too high to be readlly accessed from outside. I just laugh when she complains about that cardinal-some help I am! Think I'll hang a mirror up for her. Here I had problems with cowbirds hanging out on the car mirrors, only problem is the mess they leave behind. So I bolted an old car mirror near the bird feeder, no more problem. A real gathering place for these birds in the spring/summer, sometimes a dozen will fight for the chance to sit in front of it.