Crows are birds, too, and very interesting. I don't consider them opponents. My rule of thumb: Rodents, no; Birds, yes
They are opponents in my yard. Corvids are an intelligent family of birds; only parrots demonstrate higher problem solving abilities - but that same intelligence has resulted in feeders lying on the ground or stripped clean on their stands. I've seen them tear baby rabbits and fledgling mourning doves to pieces with the full audio accompaniment of screaming and distress cries. I generally don't like to anthropomorphize, but their arrival is like having a Mongol horde descending on a Perkins Restaurant.
Don