How can I train my budgies not to fly into the window?

I just want to know now so when their flight feathers are grown fully back I can train them not to fly into the window
Chain there wing to the cage?
Put some stickers or something like that on the pane so they can see them..or just keep the curtains closed :)
Answers:    I had the same problem until a nice person told me, he told me to draw on the skylight with white board markers (but take the birds within a different room so don't smell the odor of the markers, even though birds have a poor sense of smell, I'm pretty sure they can smell that strong stuff). Or yeah what that other dude said, stickers that stick out so they can see it.
I drew my mongoose characters on my glass and they don't fly into the window anymore... yay! ^^
hope this helps :D
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