bird brain

This bird apparently has a nest nearby. I live in a 4th story condo with a balcony, and whenever the cat goes out there, the bird freaks out and alerts the rest of the birds in the neighborhood - sometimes even attacking the cat. We are on a 4th story condo - the only way the cat poses a threat to the bird is if the bird gets too close. Except of course, when the bird starts squawking even when the cat is inside looking through the sliding glass door.