Even when the estimates of birds seen are assumed to be accurate, data interpretation is complex. Lack of information on diurnal rhythms adds difficulty to data interpretation. Counts of burrow-nesting birds (e.g., puffins) have been inaccurately interpreted because of the lack of understanding of their nesting ecology. Gulls (_Larus_ spp.), terns, and jaegers (_Stercorarius_ spp.) are not well known since shore parties have seldom investigated island interiors. Nocturnal species (e.g., ancient murrelet, _Synthliboramphus antiquus_, and storm-petrels, _Oceanodroma_ spp.) are perhaps the least known. Since only crude estimates of colony sizes are available, broad limits are used in this paper to describe known colonies.
Status and Distribution of Breeding Seabirds
Even from the sparse literature available, it is apparent that some seabird populations are now drastically different from those in the Aleutians around 1900. Changes in nesting habitat due to volcanic eruptions, tidal waves, marine erosion, and earthquakes have occurred for centuries, and colonial nesting bird populations have fluctuated accordingly. In addition, native Aleuts used marine birds and their eggs for food and their skins for clothing, but the Aleuts were so diminished in numbers by 1900 that they have had little recent effect on the bird populations.
From about 1900 to 1936, arctic foxes were introduced to most of the Aleutians for fur farming. The foxes lived on birds in summer, and some species (e.g., Aleutian Canada geese, _Branta canadensis leucopareia_) were wiped out wherever foxes were introduced. Ground-nesting and some burrow-nesting seabirds were also drastically reduced or extirpated on many islands.
During World War II the thousands of troops in the Aleutians brought dogs and cats to some of the islands as pets, and many of the animals were set free when the men departed. The military also accidentally introduced Norway rats to some of the islands. Their role in seabird population reductions is unknown.
Figures 2-15 (pages 40-46) present data on the distribution of populations of birds that have survived the foxes and other introduced predators. An annotated list of seabirds breeding in the Aleutians follows.