Pet Birds and Windows

hey all! I hope this is the right place to ask this kind of question.

So I've always had my curtains closed when my birdie is out of his cage - they still let plenty of light through and I've been worried Pico might fly into the window if I left it uncovered. But I've seen so many other bird owners just leave their curtains open? Do you think it is safe?

I saw a lot of birds enjoy sitting on the windowsill and looking outside... Does anyone have any experience or advice regarding this? Thank you :)

(edit: formatting)