Strange Birds Circling My House

I tried to take a good picture of these birds to no avail.Then I tried to find something on the internet about this strange occurrence. There were approximately 15 to 20 birds. They had an erratic flight pattern. They darted and turned a lot in all directions,but still in a circling manner,over my house.The closest I came to finding anything helpful on the internet, was different explanations of why birds fly in circles. One site said it was a sign of an incoming storm. Another said it was the updraft of the wind in which birds hitch a ride to get to their destination.I wouldn't have paid any attention at all to this behavior, except these particular birds were different from any birds I had ever seen in this area, that I'm aware of anyway. They were fairly large. with long slender wings,slightly bent in the middle, and they had a white square of sorts in the middle of each wing when out stretched. I had hoped to see one of the birds light, so I could get a better picture, but no luck there either.

 I have drawn a sketch of how the bird looked to me,but other than that I have no clue as to what kind of birds they were.They reminded me of seagulls, but a much slimmer body and wings.I may never know the real truth behind this strange occurrence.They were gone as quickly as they came. They only circled my house and property for about ten minutes that I was aware of, then they were gone.Maybe I will get lucky, and stumble across additional information in the future.