This is what the internet was made for.
@jcrabapple deeply disappointed that he leaves out two obvious alternatives - an arc because the bird was flying up to the roof and 'lightened its load' shortly after takeoff or shortly before landing, or the equally possible 'blinds were open, bird smacks into the window with explosive consequences' then staggers away after a bit of recovery.
@fencepost @jcrabapple
you'd see a bird shaped stain on the window, unless it was an unusually clean bird
@goleztrol @jcrabapple I know doves tend to be dusty, not so sure about some of the songbirds - and I think it'd be really obvious on blackbirds