We keep the feeder about 20 ft away from the house

[question everything]

but there are shrubs close to the house and on occasions a bird flies into a window and I sometimes find feathers stuck to the glass. One day I was standing close to the window and a sparrow, or a black cap chickadee at the last minute veered away.

But now I found this patters of smears forming a part of a circle on the window by the porch. I think this was made by a bird, and I have no idea what it is or why it was flying into the window.

Any ideas?

[secondwind]

1. Birds tend to see a continuation of the outside reflected

in windows, and they fly right into them. Thousands of bird die every year. We put decals on our glass windows.

[CANADIANBEAVER69]

2. Hang something on the window

We had birds flying into a big plate glass window at our work. We ended up hanging nice ornaments onto the window and the birds stopped flying into it.

[eppur_se_muova]

3. Looks like when tail feathers brush the glass, and leave an oily smear ...

You could try these UV-visible stickers made just for the purpose:

https://windowalert.com/

It also helps to hang venetian blinds, and try not to open big windows on both sides of the house. Birds see a 'tunnel' through the house and try to go through.

I assume these are windows where there's no point in covering them with a screen.

[question everything]

4. Thank. At night we draw the curtains on them but during the day we let the sun in

This is the first time we noticed since there is a porch in front of them. We often put peanuts in the corner for the squirrels (we feed all of them) and the blue jays try to grab. These may have been caused by the jays.