Data collection under the Bird Study #6 work plan occurred between July of 2010 and July of 2011, in each calendar month except January. Ship-based surveys were conducted by Defenders of Wildlife under contract to the U.S. Fish and Wildlife Service. Observers were placed on vessels of opportunity (i.e., vessels being used for other Deepwater Horizon NRDA studies in the open ocean) and recorded bird observations while the vessels were underway and stationary as they carried out their NRDA missions. Observers documented the number of pelagic seabirds encountered along the ships’ paths during both transect surveys (i.e., where field observations were documented along a transect while the ship was moving) and point count surveys (i.e., where field observations were documented from a stationary location). During the effort, field observations (including the number and species of birds encountered as well as the oiling condition of the birds, when possible) were recorded on field datasheets and photographs of the birds were taken. The primary goals of the study were to determine the number of live oiled birds in the pelagic zone and to estimate population densities of pelagic seabirds in the study area. Additional details about the surveys and results are provided in the End of Study Report (“Pelagic Seabird Density and Vulnerability to Oiling from the Deepwater Horizon/MC 252 Spill in the Gulf of Mexico”).