I am going to agree with the others, though I know it's not what you are hoping they would say. Like others have said, even if the horses didn't get spooked, they should be kept on your property only (unless the owners like them and don't mind, which they already told you that they do). Perhaps you can put up some kind of barrier to prevent them from going over there, especially now that they are laying traps for your birds. In a legal fight, you would not win if they were on their property.