Birds on a String

Driving to work this morning, I saw some birds overhead. They looked like they were suspended in mid air. It seems that they were really just sitting on a thin telephone wire. Since traffic was at a standstill, I had time to  stare at them. They were all motionless, just "chilling out". The odd thing was that they lined themselves up equally distant from each other. The same amount of space in between each bird. Did they do this to account for their wing span? Or do birds, like humans, just need their personal space.