[Illustration: =Fig. 1.= The Aleutian Islands.]
O. J. Murie, U.S. Biological Survey, made the most complete survey of the Aleutians (Murie 1959). He specifically recorded seabird colonies, spending parts of four summers in the area. Murie visited every large Aleutian island and most small ones. He recorded nearly every major colony of cliff-nesting or talus-nesting seabirds known in the Aleutians, but seldom gave sizes of colonies, and separate colonies on a particular island were often not differentiated.
World War II brought several ornithologists to the Aleutians. Cahn (1947), Sutton and Wilson (1946), Taber (1946), and Wilson (1948) provided accounts of birds observed at specific locations. After the war, Fish and Wildlife Service personnel--including I. N. Gabrielson (Gabrielson and Lincoln 1959), K. W. Kenyon (Kenyon 1961), and R. D. Jones (Refuge Narrative Reports 1949-1970)--recorded observations of breeding seabirds at several locations in the Aleutians. Investigations associated with Atomic Energy Commission nuclear testing at Amchitka Island provided the first ecological study of avifauna of an Aleutian island (White et al. 1977). Byrd et al. (1974) provided a list of birds at Adak.
In 1971, the Near Islands were surveyed by U.S. Fish and Wildlife personnel in a Cape Cod dory. In 1972, the Aleutian Islands National Wildlife Refuge obtained a vessel, the _Aleutian Tern_, which allowed visits to all parts of the island chain. That year, nearly every large island as far west as Buldir was visited, and seabird colonies were mapped. Every island has been visited at least once since 1972.
In estimating the current status of seabirds in the Aleutians, all available data were considered. Most of the information used, however, is from surveys conducted by the U.S. Fish and Wildlife Service (1970-75, unpublished data). Because these surveys only incidentally included Unimak, Akun, Akutan, Unalaska, and Umnak islands, data for these areas are almost totally lacking. Data for Bogoslof, Adak, Amchitka, Buldir, Agattu, Nizki, Alaid, and Attu are most accurate because fairly intensive investigations have been conducted there since 1970.
The available data are of unknown accuracy. The method used by most investigators who have surveyed areas in the Aleutians for seabird colonies has been to circle islands in a ship or small boat; when a colony was encountered, they simply estimated the number of birds they saw at the time. The accuracy of the estimates is affected by weather, distance from the colony, density of birds, ability and experience of the observer, and other variables. Estimates of kittiwakes and cormorants should be the most accurate, since nests were actually counted. Murres (_Uria_ spp.) are readily visible on the cliffs, but the percentage of breeders on the cliffs at a particular time of day during a particular part of the breeding season is not known. Auklet numbers are perhaps hardest to estimate, since swirling "clouds" of birds are encountered.