I spent the day doing errands off island today, but this little goldfinch was back at our dining room window for day number 3 of strange behavior.
He seems to be defending his domain, as described on the Wikipedia site about goldfinches:
“While the nest is being constructed, the male will act aggressively toward other males who intrude into his territory, driving them away, and the female reacts in the same way toward other females. This aggressiveness fades once the eggs have been laid.“
He is not crashing himself into the window, but flying up and down against the glass as if to ward off the foe that matches his every move. Sometimes I have days like this too. I feel so defensive and testy, only to realize that I just I spent the day doing battle with myself.