Squealing Pigs?

Passing through Effingham, Illinois I have stayed at the TA truck stop several times. I could not help but notice what sounded like pigs squealing. I also thought maybe the sound was brakes on trucks coming to a stop. One day I asked one of the other truck drivers what that noise was, and he replied, "Hawks". I said, "Hawks?, I thought it sounded like pigs squealing." He laughed and told me that they put speakers in the TA sign and play Hawk sounds through them to keep the birds out.