Annette Prince, director of the Chicago Bird Collision Monitors, said her organization first was notified of the injured birds along the 600 block of West Harrison Street on Sunday afternoon. Because of the unusually high number of birds, it first seemed people were the obvious culprits, she said. Prince on Monday said these types of deaths most often happen on a smaller scale — and oftentimes the falls are accidental with young birds trying to fly beyond their capability or testing their legs, only to lose their balance. But finding shattered eggs on the sidewalk seemed to rule out a fall.