Rock Island is on the Columbia River above John Day Dam near the Town of Irrigon (OR), and is owned and managed by the U.S. Fish and Wildlife Service as part of the Umatilla National Wildlife Refuge. Rock Island is a small, low-lying gravel island (ca. 0.5 acre) that was created by the John Day Dam impoundment and is part of the Blalock Island complex. The first documentation of Caspian terns nesting on Rock Island was in 2005, when 6 breeding pairs attempted to nest and has grown to ca. 80 breeding pairs in 2009. Caspian terns continue to attempt to nest on Rock Island, but nesting success has remained low due to a variety of factors, including mink predation, avian predation, and fluctuating water levels in the John Day Pool. About 700 pairs of ring-billed gulls also use Rock Island as a nesting site.
