Gulls flock to Pittsburgh's three rivers near the North Shore on Friday, Jan. 30, 2015. The gulls have migrated from the frozen Great Lakes to the open waters of the Allegheny, Monongahela and Ohio Rivers of Pittsburgh. Estimates put the flock's size as high as 7,000 and comprising of many different species of gulls including ring-billed, herring gull, Iceland gull, glaucous gull and lesser and greater black-backed gulls and kelp gull. Read more about the visiting gulls in the  Pittsburgh Tribune-Review.