MYSTERY – Anyone know the answer?

Why do seagulls stand in long lines all facing the same way?

Yesterday there were two huge long lines of seagulls, each line about an eighth of a mile long (the length of the field). The mystery was, why were they all facing the same way? They were standing shoulder to shoulder, and one line was behind the other. If one seagull had decided to turn round and face the other way would they all have followed suit so that they were all facing the same way again?

Anyone know why they allbface the same way?