Robin staring at window.

I was wondering if I could have some insight about robin behaviour. We have a bay window with a bush outside it where a robin has been repeatedly staring at itself. It doesn’t attack the window or show any aggressive behaviour. Instead it pecks at one or two leaves, taps the window and hops around the bush. It mostly just stares at itself or into the house. I have also heard it make the dog whistle sound, which I believe is a warning sound. However, there are no surrounding dangers. It just sits in the bush and squeaks. Could you please give me some insight on this behaviour.