We sometimes get wing-marks that look like that on the window. It's where a bird takes off and flies straight into it. It happened to a female blackbird and it just fell stunned onto the patio. You could almost see the stars revolving around its head ..poor thing. I put some food and water next to it and placed a washing basket over the top of it weighted it down with bricks. This being to keep the cats and foxes from getting it overnight. I thought it would be dead by morning anyway.
Next day, I removed the washing basket. The blackbird paused a while and then flew away. Must have been made of sturdier stuff than I thought.
